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We evaluate tropical cyclones (TCs) in a set of thermodynamic global warming (TGW) simulations over the continental United States (CONUS). A 12 km simulation forced by ERA5 provides a 40-year historical (1980–2019) control. Four complimentary future scenarios are generated using thermodynamic deltas applied to lateral boundary, interior, and surface forcing. We curate a data set of 4,498 6-hourly TC snapshots in the control and find a corresponding “twin” in each counterfactual, permitting a paired comparison. Warming results in an increase in mean dynamical TC intensity and moisture-related quantities, with the latter being more pronounced. TC inner cores contract slightly but outer storm size remains unchanged. The frequency with which TCs become more intense is only moderately consistent, with snapshots having increased hazards ranging from 50% to 80% depending on warming level. The fractions of TCs undergoing rapid intensification and weakening both increase across all warming simulations, suggesting elevated short-term intensity variability.

El Niño–Southern Oscillation (ENSO) influences seasonal Atlantic tropical cyclone (TC) activity by impacting environmental conditions important for TC genesis. However, the influence of future climate change on the teleconnection between ENSO and Atlantic TCs is uncertain, as climate change is expected to impact both ENSO and the mean climate state. We used the Weather Research and Forecasting Model on a tropical channel domain to simulate 5-member ensembles of Atlantic TC seasons in historical and future climates under different ENSO conditions. Experiments were forced with idealized sea surface temperature configurations based on the Community Earth System Model (CESM) Large Ensemble representing: a monthly varying climatology, eastern Pacific El Niño, central Pacific El Niño, and La Niña. The historical simulations produced fewer Atlantic TCs during eastern Pacific El Niño compared to central Pacific El Niño, consistent with observations and other modeling studies. For each ENSO state, the future simulations produced a similar teleconnection with Atlantic TCs as in the historical simulations. Specifically, La Niña continues to enhance Atlantic TC activity, and El Niño continues to suppress Atlantic TCs, with greater suppression during eastern Pacific El Niño compared to central Pacific El Niño. In addition, we found a decrease in the Atlantic TC frequency in the future relative to historical regardless of ENSO state, which was associated with a future increase in northern tropical Atlantic vertical wind shear and a future decrease in the zonal tropical Pacific sea surface temperature (SST) gradient, corresponding to a more El Niño–like mean climate state. Our results indicate that ENSO will remain useful for seasonal Atlantic TC prediction in the future.

Tornadoes are a co-occurring extreme that can be produced by landfalling tropical cyclones (TCs). These tornadoes can exacerbate the loss of life and property damage caused by the TC from which they were spawned. It is uncertain how the severe weather environments of landfalling TCs may change in a future climate and how this could impact tornado activity from TCs. In this study, we investigated four TCs that made landfall in the U.S. and produced large tornado outbreaks. We performed four-member ensembles of convective-allowing (4-km resolution) regional climate model simulations representing each TC in the historical climate and a mid-twenty-first century future climate. To identify potentially tornadic storms, or TC-tornado (TCT) surrogates, we used thresholds for three-hourly maximum updraft helicity and radar reflectivity, as tornadoes are not resolved in the model. We found that the ensemble-mean number of TCT-surrogates increased substantially (56–299%) in the future, supported by increases in most-unstable convective available potential energy, surface-to-700-hPa bulk wind shear, and 0–1-km storm-relative helicity in the tornado-producing region of the TCs. On the other hand, future changes in most-unstable convective inhibition had minimal influence on future TCT-surrogates. This provides robust evidence that tornado activity from TCs may increase in the future. Furthermore, TCT-surrogate frequency between 00Z and 09Z increased for three of the four cases, suggesting enhanced tornado activity at night, when people are asleep and more likely to miss warnings. All of these factors indicate that TC-tornadoes may become more frequent and a greater hazard in the future, compounding impacts from future increases in TC winds and precipitation.

This paper analyzes the formation dates of the nth storm in a sequence for all named North Atlantic tropical cyclones (TCs) and assesses whether the intraseasonal length of the Atlantic hurricane season has changed temporally. The record-breaking 2020 season, with 30 named storms, set records for the earliest third TC formation (Cristobal) and from the sixth TC (Fay) onward. Analysis of season length from 1851 to 2022 identifies only one statistically significant breakpoint detected in the early 1970s, roughly coinciding with the introduction of satellite observations. Since 1970, we also find a trend toward longer North Atlantic hurricane seasons. The 1971–2022 trend is robust and statistically significant, whether assessed as the number of days between the first and last storm or by the distance between intermediate percentiles (e.g., 10th–90th and 15th–85th). These increases are mainly associated with storms forming earlier in the calendar year and are best described as an upward trend rather than a stepwise shift between eras. Although a simple trend fits better than a stepwise model, improvement falls short of significance, so we do not formally reject the stepwise hypothesis. If, following this hypothesis, the 1950–2022 period is segmented into a high-activity era (HAE1; 1950–69), a low-activity era (LAE; 1970–94), and second high-activity era (HAE2; 1995–2022), the median season length of HAE2 is 12 days longer than in the first HAE, but this difference is not statistically significant (p = 0.58) and could be explained by the substantial difference in the observational network. The median season length in both HAE1 and HAE2 are significantly longer (by 36 and 48 days, respectively) than the intervening LAE. [ABSTRACT FROM AUTHOR]

Recent several studies have focused on the predictability of tropical cyclone track forecast. As a response to the question issued by Landsea and Cangialosi about whether "the approaching limit of predictability for tropical cyclone (TC) track prediction is near or has already been reached," Zhou and Toth (hereafter ZT20) and Yu et al. (hereafter Y22) have found that the limit of predictability for TC track prediction has not been reached in both the Atlantic (ATL) and western North Pacific (WNP) basins. However, the predictabilities are different in the two basins, as ZT20 found that 1 day's improvement can be obtained through 10 years in ATL, while Y22 found that 2 days' improvement can be obtained through 15 years in WNP. To reveal the causes of this difference, the predictability of TC track in WNP is first investigated under the same framework as ZT20. Then, important parameters that determine the predictabilities are found and analyzed. Results suggested that the growth rate of true track forecast error in WNP is higher than that in ATL, indicating a lower predictability in WNP. Further explorations suggested that TCs in the WNP basin have averagely larger sizes, stronger intensities, lower-latitude locations, and poorer forecast skills of their guided flows. All these factors contribute to the larger track forecast error growth rate. Moreover, it is pointed out that the improvement of forecast skills over years is mainly due to the reduction in initial analysis errors; although a lower predictability is found in WNP, the forecast skill improvement in WNP is faster than that in ATL. SIGNIFICANCE STATEMENT: Apart from its theoretical appeal, the predictability of tropical cyclone (TC)'s track is of practical interest to the forecast community and a seasonal concern for tens of millions of potentially impacted coastal residents. An investigation into the reasons for different predictabilities in the western North Pacific and Atlantic oceans would help the government to make allocation decisions for research and development investments associated with future TC forecast improvements. [ABSTRACT FROM AUTHOR]

Following a previous study examining the influence of an upper-tropospheric cold low (CL) on the track of a nearby tropical cyclone (TC), this study investigates the impacts of a CL on TC intensity. The results suggest that the relative position and separation distance between the CL and the TC are the key factors affecting TC intensity. When located outside the CL's radius of maximum winds (RMW) but within its circulation, TCs initially in the northwest quadrant of the CL intensify faster than those in the other quadrants. The β effect causes the CL to move northwestward toward the TC and enhances eddy angular momentum flux convergence. Meanwhile, the upper-level TC outflow erodes the CL and reduces the associated vertical wind shear, promoting TC intensification. In contrast, for TCs initially located southeast of the CL, the attraction of the Fujiwhara effect between the two entities counteracts the CL's β drift and helps to maintain their separation distance. Moreover, Rossby wave energy dispersion induces an anticyclone southeast of the CL, which transports lower-θe air toward the TC and hinders the TC development. Furthermore, TCs within the CL's RMW reach a similar intensity due to their PV superposition, irrespective of their relative positions to the CL. For TCs located outside the CL circulation, the CL's impacts are largely negligible for TCs located northwest of the CL, but TCs located southeast of the CL may still be affected by the CL-induced anticyclone. Significance Statement: This study examines the influence of an upper-tropospheric cold low on tropical cyclone intensity. The results illustrate that the relative position and separation distance between the cold low and tropical cyclone are crucial factors in determining tropical cyclone intensity. Tropical cyclones initially northwest of a cold low intensify faster than those to the southeast when located outside the cold low's radius of maximum winds but still within its circulation. The main mechanisms are how the β steering and interactions between the two entities act together. The midlevel intrusion of cold, dry air and Rossby energy dispersion also contribute to their complex interaction. These insights provide a guide for forecasting the tropical cyclone intensity when influenced by a nearby upper-level cold low. [ABSTRACT FROM AUTHOR]

Aim: Shoaling of large oxygen minimum zones (OMZs) that form along eastern margins of the world's oceans can reduce habitat availability for some pelagic fishes. Our aim was to test the hypothesis that habitat compression caused by shoaling of the Pacific OMZ in tropical regions creates a boundary to the southern distribution of shortfin mako sharks (Isurus oxyrinchus) in the Eastern North Pacific Ocean. Location: Eastern North Pacific and Western North Atlantic oceans. Methods: We compared environmental conditions between areas used by satellite‐tagged mako sharks in the Eastern North Pacific, encompassing the world's largest OMZ, to those used in the Western North Atlantic where no OMZ is present. In the Pacific we quantified the effects of temperature and dissolved oxygen (DO) on depth use and tested if sharks spent less time in areas with strong habitat compression over the OMZ than expected by chance. Results: The southern distribution of sharks in the Pacific corresponded with the apex of OMZ shoaling in the North Equatorial Current. Sharks in the Atlantic occupied areas with warm surface temperatures (≥ 26°C) more often than the Pacific, and waters with these temperatures in the Atlantic had greater DO at depth. Sharks in the Pacific reduced time near the surface in warm temperatures and consistently avoided depths with low DO and spent less time in areas with strong habitat compression than expected by chance. Main Conclusions: The combination of warm surface temperatures and shoaling of the OMZ creates a soft boundary to mako shark movements in the Eastern North Pacific Ocean. The expected expansion of OMZs due to climate change could have considerable impact on future distribution of mako sharks and other pelagic fish. As such, development of species distribution models to predict the effects of climate change on pelagic fish distributions should incorporate oxygen availability. [ABSTRACT FROM AUTHOR]

Short-term events like tropical cyclones often have a strong impact on the upper ocean, causing transient changes in the physical and chemical properties of the sea. These changes could potentially affect the distribution pattern of the phytoplankton community. The present study aims to investigate the impact of the distribution of phytoplankton size classes (PSCs) caused by the tropical cyclonic event Ockhi in the Arabian Sea (AS) in 2017. Multiple datasets, including satellite remote sensing and reanalysis data, were utilized to observe the biogeochemical variability and the corresponding changes in PSCs distribution caused by the Ockhi cyclone event. One of the predominant issues in using satellite remote sensing data is the loss of data due to overcast conditions, which was resolved by reconstructing the chl-a and SST using an empirical orthogonal function. The results show a short-term shift in the PSCs pattern from the pico and nano-rich region to the micro-dominated environment in the cyclone passage region during the post-cyclone period. When comparing the results with the physical and biochemical parameters, it was found that the cyclonic event triggered the deep-seated nutrients to the surface, which promoted favourable conditions for microorganisms to proliferate for a short span in the cyclone passage region. The overall study highlights the impact of the Ockhi cyclone on biogeochemical changes and corresponding shifts in the phytoplankton size distribution along the cyclone path. [ABSTRACT FROM AUTHOR]

Analysis of the daily rainfall records from 43 synoptic stations of the Philippine Atmospheric Geophysical and Astronomical Services Administration (PAGASA) from 1979 to 2019 reveals that the wettest station in the Philippines is in Hinatuan, Surigao del Sur, in eastern Mindanao Island in terms of the mean annual total rainfall. Despite being located at a low elevation (∼ 3 m above sea level), the mean annual total rainfall in this station is about 4554 mm, which is approximately 700 mm more than the mean annual total rainfall in Baguio City station, the station with the highest elevation (∼ 1500 m above sea level) in the country. Further analysis of the statistical characteristics of rainfall and comparison with other stations in terms of intensity, frequency, duration (i.e., short (1 − 2 days), medium (3 − 7 days), long (8 − 14 days), and very long (> 14 days) events), and 95th percentile extremes show that this station ranks first in terms of the frequency of wet months (200–500 mm month− 1) and heavy rainfall months (> 500 mm month− 1), mean monthly rainfall amounts from January to April, and the mean rainfall amount in the short duration category. The contributions of multiscale factors such as Tropical Cyclones (TCs), Low Pressure Systems (LPSs), and the Madden-Julian Oscillation (MJO) to the rainfall extremes over Hinatuan station are also quantified. The results show that TCs, LPSs, and MJO contribute about 0–5%, 0–38%, 3–38% to the monthly extremes over Hinatuan station, respectively. Cases when TCs or LPSs are located within 1100 km radius centered at Hinatuan station while MJO is active were also found and their contributions to the monthly extremes are 0–4% and 0–12%, respectively. The largest portion of the extremes are associated with other unaccounted factors, which contribute about 49–71%. The results of this study may serve as a basis for future characterization of the spatial variation of rainfall including the variations in extremes and their potential causes over the Philippines [ABSTRACT FROM AUTHOR]

Significant advancements in the development of machine learning (ML) models for weather forecasting have produced remarkable results. State-of-the-art ML-based weather forecast models, such as FuXi, have demonstrated superior statistical forecast performance in comparison to the high-resolution forecasts (HRES) of the European Centre for Medium-Range Weather Forecasts (ECMWF). However, a common limitation of these ML models is their tendency to generate increasingly smooth predictions as forecast lead times increase, which often results in the underestimation of intensities of extreme weather events. To address this challenge, we developed the FuXi-Extreme model, which employs a denoising diffusion probabilistic model (DDPM) to enhance finer-scale details in the surface forecast data generated by the FuXi model in 5-day forecasts. An evaluation of extreme total precipitation (TP), 10-meter wind speed (WS10), and 2-meter temperature (T2M) illustrates the superior performance of FuXi-Extreme over both FuXi and HRES. Moreover, when evaluating tropical cyclone (TC) forecasts based on International Best Track Archive for Climate Stewardship (IBTrACS) dataset, both FuXi and FuXi-Extreme shows superior performance in TC track forecasts compared to HRES, but they show inferior performance in TC intensity forecasts in comparison to HRES. [ABSTRACT FROM AUTHOR]

Tropical cloud clusters (TCCs) can potentially develop into tropical cyclones (TCs), leading to significant casualties and economic losses. Accurate prediction of tropical cyclogenesis (TCG) is crucial for early warnings. Most traditional deep learning methods applied to TCG prediction rely on predictors from a single time point, neglect the ocean-atmosphere interactions, and exhibit low model interpretability. This study proposes the Tropical Cyclogenesis Prediction-Net (TCGP-Net) based on the Swin Transformer, which leverages convolutional operations and attention mechanisms to encode spatiotemporal features and capture the temporal evolution of predictors. This model incorporates the coupled ocean-atmosphere interactions, including multiple variables such as sea surface temperature. Additionally, causal inference and integrated gradients are employed to validate the effectiveness of the predictors and provide an interpretability analysis of the model's decision-making process. The model is trained using GridSat satellite data and ERA5 reanalysis datasets. Experimental results demonstrate that TCGP-Net achieves high accuracy and stability, with a detection rate of 97.9% and a false alarm rate of 2.2% for predicting TCG 24 hours in advance, significantly outperforming existing models. This indicates that TCGP-Net is a reliable tool for tropical cyclogenesis prediction. [ABSTRACT FROM AUTHOR]

This study investigates the large-scale circulation anomalies induced by straight-moving tropical cyclones (TCs) over the western North Pacific (WNP) during winter. Corresponding to the straight-moving TCs, quasi-stationary wave trains appear as alternative geopotential height anomalies in the upper troposphere stretching from East Asia to the North Pacific. Specifically, the anomalous anticyclones are initially formed to the south of Japan and then lead to the subsequent anomalies over the Sea of Okhotsk and the Gulf of Alaska, respectively. Further analysis reveals that the upper-level anticyclonic anomalies are excited by negative Rossby wave sources, which are mainly attributed to the poleward vorticity advection by anomalous divergence relevant to TCs. In addition, the diagnosis indicates that the generation of wave source is caused by the product of the TC-induced divergent flows and the prominent meridional vorticity gradient in association with East Asian upper-tropospheric westerly jet. These findings imply that the tropical disturbances over the WNP, such as straight-moving TCs, can remotely affect weather over the extratropics, and thus have implications for improving the weather forecast over the extratropics through improving tropical disturbance forecast. [ABSTRACT FROM AUTHOR]

Tropical cyclone (TC) risk often varies with changes in the distribution of TC energy within and between basins. Little is known how global tropical cyclone energy is redistributed under global warming. By studying the contribution of individual basin TCs to the global TC activity, the study reveals the process of energy redistribution among different tropical cyclone categories. Results indicate that the distribution of accumulated cyclone energy (ACE) varies among the different tropical cyclone categories in a given basin. The percentage of the ACE in an individual basin has undergone significant redistribution over several decades. The changes in impact factors in specific basins during the active tropical cyclone season are discussed in relation to those factors in other basins, and they are found to vary among the basins. Furthermore, the models from the Coupled Model Intercomparison Project Phase 6 (CMIP6) show trends in the distribution of TC energy in the future. [ABSTRACT FROM AUTHOR]

Idealized numerical simulations have been carried out to reveal the complexity in the development of asymmetric convection in a tropical cyclone (TC) under the influence of an environment with either uniform flow, vertical wind shear (VWS), or both. Results show that rainwater is enhanced to the right of the motion in the outer rainband, but such enhancement occurs in the upshear-left area of the inner-core region. Additionally, due to the asymmetries introduced by environmental flow, wavenumber-1 temperature and height anomalies develop at a radius of ~1000 km in the upper levels. A sub-vortex aside from the TC center encompassing the wavenumber-1 warm center appears, and asymmetric horizontal winds emerge, which, in turn, changes the storm-scale (within 400 km) VWS. Deep convection in the inner core closely follows the changing storm-scale VWS when its magnitude is larger than 2 m s–1 and is located downshear of the storm-scale VWS in all the experiments with environmental flow. In the outer rainbands, the maximum boundary layer convergence is mainly controlled by the direction of motion and is located in the rear-right quadrant. These results extend upon the findings of previous studies in three aspects: (1) The discovery of the roughly linear combination effect from the uniform flow and large-scale VWS; (2) The development of upper-level asymmetric winds on a 1000-km scale through the interaction between the TC vortex and environmental flow, resulting in changes in the storm-scale VWS pattern within the TC area; (3) The revelation that TC asymmetric convection closely aligns with the direction-varying storm-scale VWS instead of the initially designated VWS. [ABSTRACT FROM AUTHOR]

In this study, a super cyclonic storm (Amphan) over Bay of Bengal was analyzed with the National Center for Medium-Range Weather Forecasting, Unified Model (NCUM) and National Center for Environmental Prediction (NCEP) global model data. Further, the weather research and forecasting (WRF) model has been utilized to simulate this super cyclonic storm with NCUM and NCEP data as initial and boundary conditions. The model is integrated, for every 12 h interval from 16 May 0000 UTC to 18 May 1200 UTC with horizontal resolution of 9 km and vertically at 34 levels. The results reveal that the track of the cyclone, central pressure of the cyclone, intensity of the cyclone, and landfall time of the cyclone are simulated by the model reasonably well in both the cases that are with NCUM-GFS and NCEP-GFS. However, the WRF simulations with NCEP data are closer to IMD's estimated track and intensity, when compared with the simulations with NCUM data. The relatively higher errors in simulations with NCUM could be due to the differences in the initial cyclone vortex against the observation in some initial conditions. [ABSTRACT FROM AUTHOR]

Worldwide, coastal wetlands are threatened by disrupted hydrology, urbanization, and sea-level rise. In southwest Florida, coastal wetlands include tidal creeks and coastal ponds, which are the primary habitats used by juvenile Tarpon, Megalops atlanticus, an important sport fish. Coastal ponds can occur near uplands and are ephemerally connected to the open estuary, creating conditions of variable dissolved oxygen and salinity. Juveniles can tolerate wide-ranging abiotic conditions, but little is known about how they egress from their remote nursery habitats, which often requires them to cross > 1 km of mangrove forest to reach the open estuary. The objective of this study was to (1) compare Tarpon body condition among ponds close to the open estuary versus those ponds farther away on the Cape Haze peninsula of Charlotte Harbor, Florida, and (2) using acoustic telemetry determine what factors contribute to Tarpon emigration from the ponds to open estuarine waters. We tested the hypothesis that distinct groups of Tarpon occur in isolated ponds, leading to variation in fish length and body condition, and that opportunities for emigration from these ponds hinge on high water events. No pond stood out as having Tarpon of low body condition. Factors contributing to increased probabilities of Tarpon emigration were low barometric pressure, high-water level, and Tarpon body length. Tarpon emigrated from ponds near tidal creeks during summer king tides, while tropical cyclone conditions were needed to allow for movement from ponds farther in the landscape. The juvenile Tarpon were later detected at the mouths of large rivers 30 km up-estuary. The characterizations of water levels and event criteria needed for successful Tarpon nurseries should aid in habitat conservation and the creation of Tarpon nursery habitat in restoration designs. [ABSTRACT FROM AUTHOR]

This study projects the changes in tropical cyclone (TC) landfalls in the western North Pacific under shared socioeconomic pathway (SSPs) scenarios during the TC peak season by using low‐resolution global climate models participating in the Coupled Model Intercomparison Project phase 6 (CMIP6). Projections are based on the relationship between mid‐ and lower‐level atmospheric circulation and TC landfall frequency during the historical period from 1985 to 2014 and the future climate period from 2015 to 2100. The landfall areas for TCs are divided into northern East Asia (NEA), middle East Asia (MEA) and southern East Asia (SEA); the TC peak seasons are July–September for NEA and MEA, and July–November for SEA. To evaluate reproducibility, both ensemble and individual model outputs for mid‐ and lower‐level atmospheric circulations associated with TC landfall in each East Asian subregion are compared to the reanalysis. An ensemble of seven models with stable results for all three regions is more reasonable in simulating atmospheric circulation patterns than an ensemble of all CMIP6 models. The findings suggest that TC landfall is projected to increase by about 12% and 32% in NEA and MEA, respectively, in the late 21st century under the SSP5‐8.5 scenario compared to the historical period, while decreasing by 13% in SEA. These changes are consistent under both warming scenarios, and are more pronounced in the SSP5‐8.5 scenario compared to SSP1‐2.6, particularly in the later period of this century. An analysis of future atmospheric circulations suggests that global warming will weaken the western North Pacific subtropical high and cause its boundary to retreat eastward. This will lead to changes in the steering flow, which is closely related to TC tracks, resulting in TC landfalls to increase or decrease depending on the East Asian subregion. [ABSTRACT FROM AUTHOR]

This article reviews and compares popular methods, some old and some recent, that produce time series having Poisson marginal distributions. The article begins by narrating ways where time series with Poisson marginal distributions can be produced. Modeling nonstationary series with covariates motivates consideration of methods where the Poisson parameter depends on time. Here, estimation methods are developed for some of the more flexible methods. The results are used in the analysis of (1) a count sequence of tropical cyclones occurring in the North Atlantic Basin since 1970, and (2) the number of no‐hitter games pitched in Major League Baseball since 1893. Tests for whether the Poisson marginal distribution is appropriate are included. [ABSTRACT FROM AUTHOR]

This study reported the unprecedented tropical cyclone (TC) activity in the western North Pacific (WNP) and North Atlantic (NA) during the developing year of the 2023/2024 El Niño. The possible causes behind these unusual features were addressed. In contrast to previous El Niño events, an unusual low/high TC genesis number in the WNP/NA was identified during the typhoon season (June–November) in 2023. Meanwhile, the mean TC genesis location in the WNP exhibited a La Niña‐like northwestward shift, rarely observed in an El Niño developing year. An observational diagnosis on TC‐genesis‐related large‐scale dynamics and thermodynamics revealed that the lower/higher TC numbers in the WNP/NA were primarily attributed to an anticyclonic/cyclonic anomaly linked to trans‐basin sea surface temperature anomalies in the tropics and extratropics. Additionally, weaker intraseasonal oscillation activity compared to previous El Niños also partially contributed to fewer TCs in the WNP. Plain Language Summary: During the 2023 El Niño, tropical cyclone (TC) activity in the western North Pacific (WNP) and North Atlantic (NA) was unusual. Extremely few TCs formed in the WNP during the typhoon season (June–November), while more TCs were observed in the NA compared to the climatology, opposite to the feature of TC genesis in previous El Niño events. Additionally, the mean genesis location of WNP TCs shifted northwestward, contrary to the typical southeastward shift seen in past El Niño events. These anomalies were linked to an anticyclonic anomaly in the WNP and a cyclonic anomaly in the NA, which respectively hindered and facilitated favorable large‐scale environments related to TC genesis. Diagnostic analysis revealed that these circulation anomalies were associated with trans‐basin sea surface temperature anomalies (SSTAs). Extremely warm SSTAs in the northern Indian Ocean, tropical NA (TNA), and extratropical regions, along with a negative Pacific meridional mode, favored the anticyclonic anomaly in the WNP. In contrast, the extremely warm SSTA in the TNA facilitated the cyclonic anomaly in the NA. Additionally, weak intraseasonal oscillation activity also contributed to the low number of WNP TCs. Key Points: Unlike previous El Niño events, unusually fewer TCs, with a northwestward shift in genesis location, were observed in the WNP in 2023By contrast, the number of TCs in the North Atlantic (NA) was approximately twice that of the composite mean of previous El NiñosIn addition to high SST in the tropical NA and negative PMM, high extratropical SST along with inactive ISO contributed to the features [ABSTRACT FROM AUTHOR]

Tropical cyclones are among the most destructive natural disasters. However, lack of detailed observations and the simplifications inherent in operational ocean models, lead to incomplete knowledge of underlying ocean processes. Using high‐fidelity large‐eddy simulations and moored observations away from the storm track, we show that mutually interacting shear and convective processes, govern the evolving state of the upper ocean. Our simulation agrees well with observed sea surface temperature and sea surface salinity. Shear driven turbulence due to surface wind stress erodes stratification, deepens the ocean mixed layer and transports freshwater into the mixed layer during rain events. Concurrently, surface buoyancy loss also aids in ocean mixing via convective entrainment. The mixing efficiency and the associated eddy diffusivity shows high spatiotemporal variability throughout the water column during cyclone passage. Thus, a better insight into the upper ocean mixing mechanisms is necessary for developing improved mixing parameterizations for tropical cyclone intensity forecasts. Plain Language Summary: Tropical cyclones are among the most destructive natural phenomena on Earth. The powerful winds in a cyclone cause vigorous mixing in the upper ocean, cool the sea surface temperature (SST) and influence cyclone intensification. Using high‐fidelity simulations and observations, we demonstrate the synergy between ocean convection and shear driven processes to change the upper ocean state. Due to temporally varying surface forcings, the upper ocean mixing was also highly variable. Our study provides new insights into the energetics of such an extreme event where both wind stress and surface cooling are present. Key Points: Large‐eddy simulations are performed for the upper ocean during the passage of a cycloneShear and turbulent convection acted in concert to modify the upper ocean propertiesIrreversible mixing and mixing efficiency show high spatiotemporal variability [ABSTRACT FROM AUTHOR]

An accurate center localization in near real‐time is critical for tropical cyclone (TC) monitoring and forecasting. This study presents a robust algorithm for localizing typhoon centers using the Chinese geostationary (GEO) meteorological satellite. The results using the Advanced Geostationary Radiation Imager (AGRI) onboard Fengyun‐4A (FY‐4A) satellite data, achieving a mean absolute error (MAE) of 29.4 km across various typhoon intensities in the Western North Pacific, superior to other baseline methods. By harnessing the multi‐spectral imagery from the FY‐4A and incorporating an attention mechanism, it significantly boosts the deep learning convolutional neural network's ability to identify typhoon cloud features and their centers, even during their initial and weakest stages, which is laudable because these are the most difficult for center fixing even for human analysts. Remarkably, it requires just a single moment satellite imagery to locate the center of typhoon, enabling automated updates of the typhoon centers in near real‐time applications. Plain Language Summary: Understanding and observing the exact location of the typhoon's center are crucial for monitoring and forecasting the storm path and intensity. Geostationary (GEO) satellites have become the primary means of continuously observing typhoon centers with Advanced Dvorak Technique (ADT). Nevertheless, locating the center from GEO observations more quickly and accurately is still desired for operational applications. For such purpose, a new algorithm that utilizes just a single moment images from a geostationary satellite to locate the center of typhoon rapidly and accurately has been developed. This method represents a significant improvement, capable of locating the center of typhoon with a mean absolute error of only 29.4 km, outperforming existing other baseline methods. Its sophisticated design allows it to discern intricate details of cloud features from multi‐spectral satellite imagery, thus providing valuable insights particularly during the early stages of a typhoon's development. Key Points: A new and robust typhoon center localization algorithm using geostationary satellite imagerySmaller differences in typhoon center across all the intensities are found between the new locating algorithm and the best track resultsThis methodology can be applied to advanced geostationary imager data for near real‐time TC monitoring [ABSTRACT FROM AUTHOR]

Extreme integrated vapor transport (IVT) is a crucial driving factor of extreme precipitation events (EPEs). This paper presents a complex network‐based characterization of propagations from extreme IVT to EPEs. Specifically, the propagations are tracked from extreme IVT to EPEs by event synchronization; and then the source zones of extreme IVT contributing to EPEs are identified by two‐layer complex network. A case study is devised for North America based on the daily NCEP/NCAR Reanalysis 1 from 1948 to 2021. Overall, eight communities of EPEs are identified: the west coast of United States (US) tend to receive substantial EPEs from the Pacific Ocean; the Gulf of Alaska tends to receive oceanic EPEs propagating inland; western Canada typically experiences large amount of out tendencies and the EPEs tend to accumulate in the Baffin Island and Labrador Peninsula; the southeastern US and the northern Great Plains tend to experience northward propagations from Mexico. Along the west coast of North America, the propagations from extreme IVT to EPEs typically originate from the eastern North Pacific between 160°W and 110°W, and make landfalls in 4 days. These propagations are influenced by anomalous cyclonic circulations developing over the Gulf of Alaska forced by eastward Rossby waves. The coincidence rate of these propagations with atmospheric rivers is, respectively, 85.31% in autumn, 91.35% in winter, 73.94% in spring, and 64.52% in summer. Overall, the observed propagations from extreme IVT to EPEs yield insights into the mechanism of atmospheric moisture transport and the predictability of precipitation. Plain Language Summary: Owing to different synoptic systems such as atmospheric rivers, low‐level jets, and tropical cyclones, there exist profound propagations from extreme integrated vapor transport to extreme precipitation. Focusing on North America, this paper is concentrated on the complex network underlying extreme integrated vapor transport and extreme precipitation events. It is found that the Rocky Mountains play an important part in shaping the propagations from extreme integrated vapor transport to extreme precipitation events. In particular, along the west coast of North America, extreme integrated vapor transport originating from the eastern North Pacific tends to be blocked by the Rocky Mountains, causing rising/cooling and leading to extreme precipitation. Overall, along the Rocky Mountains, there exist eight communities of extreme precipitation. Key Points: There exists a complex network on propagations from extreme integrated vapor transport to extreme precipitation events in North AmericaIn the west coast of North America, the propagations typically originate from eastern North Pacific and make landfalls in 4 daysThe coincidence rate of propagations with atmospheric rivers is, respectively, above 90% and 60% in boreal winter and summer [ABSTRACT FROM AUTHOR]

It is important to understand the mechanisms of heavy rainfall events, as such information could improve forecasting of these events and help mitigate their adverse impacts on life and property. In this study, we analyzed hourly stable isotopic compositions in water vapor (δ18Ov and d‐excessv) during heavy rainfall events in the summer monsoon season (June to September) from 2013 to 2023 in Nanjing, eastern China. These data were extracted from the longest data set of high‐resolution and continuous in situ observations of water vapor isotopes globally. Based on these data, we identified four evolution patterns of δ18Ov during heavy rainfall events, corresponding to different weather systems: slow‐declining (tropical cyclone interacting with mid‐ and high‐latitude system), W‐shaped (tropical cyclone), U‐shaped (cold vortex system), and inclined L‐shaped (upper‐level trough system). The isotopic variations suggest that heavy rainfall events in eastern China were mainly sustained by moisture from adjacent oceans (including the South China Sea and the East China Sea) and terrestrial environment rather than from the distant Indian Ocean as previously suggested. In addition, for some heavy rainfall events with an intermittent period, the nearby oceanic moisture transport alters before and after the intermittent period due to an intensity change or overall transition of low‐level weather systems. This study serves as a benchmark for tracing heavy rainfall processes in East Asia using high‐resolution water vapor isotopes. Plain Language Summary: Flooding is a major source of mortality and damage in heavy rainfall events. Accurate forecasting of heavy rainfall remains a significant challenge due to inadequate understanding of the complex moisture sources and transport processes. Stable isotopes in atmospheric water vapor could provide crucial information on how water is transported and mixed in the atmosphere. The 11‐year in situ online observations of water vapor isotopes indicated that heavy rainfall events in eastern China were mainly sustained by moisture from adjacent oceans and terrestrial environment rather than from the distant Indian Ocean as previously suggested. Our results provide a valuable high‐resolution data set of water vapor isotopes for heavy rainfall events and a benchmark for tracing heavy rainfall processes in East Asia using water vapor isotopes. Key Points: δ18Ov values present four patterns under the influence of different weather systems during heavy rainfall eventsMoisture from adjacent oceans and terrestrial environment contribute greatly to the heavy rainfall events in eastern ChinaFluctuations of isotopic values before and after the intermittent period indicate the alteration of nearby oceanic moisture transport [ABSTRACT FROM AUTHOR]

Tropical disturbances frequently occur over the South China Sea and the western Pacific from May to October. Less than half of them can intensify into tropical cyclones, with the majority remaining nondeveloping. This study reveals that nondeveloping low‐level tropical disturbances within the easterly wind belt can also cause heavy rainfall over the northern South China Sea (NSCS, 110°E–120°E, 15°N–20°N) in autumn. Based on a heavy rainfall event in September 2021, physical mechanisms of intensified tropical disturbance‐induced rainfall over the NSCS are investigated. The tropical disturbance at 850 hPa initially originated within easterly winds south of the western Pacific subtropical high and was guided into the NSCS by these easterlies. Meanwhile, the South Asian high disrupted the long‐lasting cyclone‐anticyclone pairs on its southeast side, inducing divergence at 200 hPa, which enhanced the tropical disturbance. Specifically, the upper‐level divergence superimposed on the tropical disturbance intensified ascending motion and low‐level convergence. Above the tropical disturbance, convergence below 400 hPa, combined with vertical and horizontal advection above 500 hPa, together reinforced the vortex structure of the disturbance, facilitating water vapor accumulation. Further results show that cold rain processes above the freezing level were active and significantly contributed to the precipitation. This study provides new insights into heavy rainfall over the NSCS, showing that in the absence of the Intertropical Convergence Zone and cold air, upper‐level divergence promotes the vertical development of the tropical disturbance. The enhanced ascending motion and the increased midupper level moisture intensify cold rain processes and precipitation. Plain Language Summary: The South China Sea and the western Pacific are regions where tropical disturbances are prone to occur. This study reveals that low‐level tropical disturbances within the easterly wind belt, which fail to develop into tropical cyclones, can also cause heavy rainfall over the northern South China Sea (NSCS, 110°E–120°E, 15°N–20°N) in autumn. Analysis of a typical event in September 2021 reveals that the tropical disturbance at 850 hPa initially originated within the easterly winds south of the western Pacific subtropical high and was guided into the NSCS by intensified easterly winds. The precipitation induced by the tropical disturbance was weak initially, but it intensified after the disturbance entered the NSCS. This can be explained by that the South Asian high extended eastward and disrupted the long‐lasting cyclone‐anticyclone pairs at its southeast side, resulting in horizontal wind speed shear. Accordingly, upper‐level divergence formed between strong and weak horizontal wind speeds. The upper‐level divergence superimposed on the low‐level tropical disturbance facilitated ascending motion and convergence, triggering the heavy rainfall over the NSCS. Moreover, the intensified ascending motion and the increased moisture favored the active cold rain processes above the freezing level, making a crucial contribution to the precipitation. Key Points: Low‐level tropical disturbances within the easterly wind belt may cause heavy rainfall over the northern South China SeaThe tropical disturbance and the associated ascending motion tend to be enhanced by the upper‐level divergenceDeeper convection during tropical disturbance supports cold rain processes contributing to the heavy rainfall [ABSTRACT FROM AUTHOR]

Based on the 6‐hourly tropical cyclone best track and global reanalysis data, statistical analyses and a machine learning approach are used to identify/quantify factors that affect the relative weakening rate (RWR) of landfalling TCs (LTCs) over China mainland during 1980–2020. Results show that the enhanced RWR of LTC events usually occurs when LTCs move into regions with large environmental vertical wind shear (VWS), large surface roughness (SURR), high land surface soil temperature (SOILT), low surface latent heat flux (SLHF), and with relatively faster translational speeds (SPD). The SPD and SURR are dominant factors determining the RWR of LTCs over China mainland, contributing about 20% and 18.5% to the RWR of LTCs. VWS is also a key factor affecting RWR of LTCs with mid‐level VWS contributing 17.8% to RWR of LTCs and low‐ and deep‐level VWS contributing about 12.9% and 11.2%, respectively. Furthermore, factors affecting the LTC weakening rate in south and north China are different. In north China, the VWS at different levels are all highly correlated with LTC RWR after landfall, whereas the influence of mid‐layer VWS shows significant correlation with LTC RWR in south China. In addition, surface characteristics, including SURR, SLHF, and SOILT, have significant correlation with LTC RWR in south China. But the relationships between surface characteristics and LTC RWR in north China are not statistically significant. It is worth noting that although the correlation between DIV200 and LTC RWR is insignificant for the whole China mainland, it presents highly negative and positive correlations in south and north China, respectively. Plain Language Summary: In this study, statistical analyses and a machine learning approach (XGBoost) are used to identify and quantify factors affecting the relative weakening rate (RWR) of landfalling tropical cyclones (LTCs) in China mainland. Results show that the large environmental vertical wind shear (VWS, no matter in the deep‐layer or in the lower‐layer), large surface roughness (SURR), high land surface soil temperature (SOILT), low surface latent heat flux (SLHF), and faster translational speed (SPD) are key factors, which enhanced the weakening rate of LTC over China mainland. Among them, the SPD and SURR play the most important role in the LTC weakening rate over China mainland. Furthermore, factors affecting LTC weakening rate in south and north are explored. In south China, LTC weakening rate highly correlated with the surface conditions (including SLHF, SOILT, and SURR), upper‐level divergence (DIV200), and SPD. However, the main factors affecting LTC weakening rate over North China are dynamical variables, including VWS, DIV200 and SPD. Although the correlation between DIV200 and LTC RWR is insignificant for the whole China mainland, it presents highly negative and positive correlations in south and north China, respectively. Key Points: A machine learning approach is used to quantify factors affecting the weakening rate of landfalling TCsThe translation speed of TCs and the surface roughness contribute most to the weakening rate of LTCs over China mainlandThe effect of upper‐level divergence to the weakening rate of LTCs is opposite over south and north China [ABSTRACT FROM AUTHOR]

Vertical wind shear (VWS), as an important dynamic factor influencing tropical cyclone rainfall (TCR), has a remarkable diurnal cycle of variation over the East Asia–western North Pacific region. The magnitude of tropical cyclone (TC)‐experienced VWS has enhanced amplitude but different phases over the South China Sea (SCS) and coastal East China (CEC) compared with that over the open ocean. Diurnal variation in TCR over the SCS shows statistically significant correlation with that of VWS. The convection concentrated in the downshear‐left quadrant strengthens markedly when VWS becomes large, thereby delaying the peak rainfall in the inner core of the TC and enhancing the amplitude of the diurnal cycle of TCR at ~09 local standard time. Over CEC, the diurnal signal of TCR is very weak but statistically significant in the downshear‐left and upshear‐right quadrants with opposite phase, illustrating the change in asymmetry of the spatial distribution of TCR induced by the large VWS diurnal cycle. The findings of this study could provide reference for improved forecasting of TCR on the fine temporal scale. [ABSTRACT FROM AUTHOR]

ABSTRACT Rapid expansion (RE) of tropical cyclones (TCs) is a structural evolution that specifies the dramatic geometric synthesis increase in TC size. Its destructive potential is comparable or even more pronounced than that by the TC rapid intensification but receives limited attention. In this study, we utilise the ERA5‐derived 41‐year (1979–2019) global climatology of TC outer size data (i.e., effective azimuthal‐area‐average radius of 34‐kt gale‐force surface winds, R34EFF) to define RE and reveal the global climatology of RE for the first time, where RE is defined as the 90th percentile of global expanding samples (i.e., ΔR34EFF > 50 NM per 24 h; 1 NM = 1.852 km). Statistics show that 32% of all TCs underwent RE at least once during their lifetime. Climatologically, the proportion of RE decreased significantly in the globe (7%) and Northern Hemisphere (9%), particularly in the western North Pacific (8%). Seasonally, the RE proportion peaks in the early and late TC seasons. Spatiotemporally, distinct spatiotemporal variations and interdecadal changes of RE are found. In view of TC lifecycle, TCs likely reach their lifetime maximum intensity and lifetime maximum size after RE initiation. The duration of RE varies widely from basin to basin, while its seasonal variability is relatively smaller. Regarding the relationship between RE and TC intensity, the intensity of rapidly expanding TCs may increase or decrease with the former being more likely. The initial size and intensity of rapidly expanding TCs tend to be small (45 NM) and weak (60 kt), respectively. This study advances the understanding of RE from a global perspective, laying important groundwork for future study. [ABSTRACT FROM AUTHOR]

Quantitative precipitation forecasts (QPF) from numerical weather prediction models need systematic verification to enable rigorous assessment and informed use, as well as model improvements. The United States (US) National Oceanic and Atmospheric Administration (NOAA) recently made a major update to its regional tropical cyclone modeling capabilities, introducing two new operational configurations of the Hurricane Analysis and Forecast System (HAFS). NOAA performed multi-season retrospective forecasts using the HAFS configurations during the period that the Hurricane Weather and Forecasting (HWRF) model was operational, which was used to assess HAFS performance for key tropical cyclone forecast metrics. However, systematic QPF verification was not an integral part of the initial evaluation. The first systematic QPF evaluation of the operational HAFS version 1 configurations is presented here for the 2021 and 2022 season re-forecasts as well as the first HAFS operational season, 2023. A suite of techniques, tools, and metrics within the enhanced Model Evaluation Tools (METplus) software suite are used. This includes shifting forecasts to mitigate track errors, regridding model and observed fields to a storm relative coordinate system, as well as object oriented verification. The HAFS configurations have better performance than HWRF for equitable threat score (ETS), but larger over forecast biases than HWRF. Storm relative and object oriented verification show the HAFS configurations have larger precipitation areas and less intense precipitation near the TC center as compared to observations and HWRF. HAFS QPF performance decreased for the 2023 season, but the general spatial patterns of the model QPF were very similar to 2021-2022. [ABSTRACT FROM AUTHOR]

Subduction of water masses serves as a critical linkage between the surface and subsurface ocean, playing a crucial role in redistributing heat, carbon, and nutrients in the ocean. This process significantly influences global climate and marine ecosystem dynamics. Analyzing five ocean reanalysis data sets, we reveal a distinctive see‐saw pattern in anomalous subduction rates between western and eastern Subtropical Mode Water (STMW) formation areas. This pattern is predominantly driven by variations in latent heat flux, which modulates the late‐winter mixed layer depth. We demonstrate that late‐winter Aleutian Low (AL) activity induces these anti‐phase variations through its impact on latent heat flux. Notably, the Pacific Decadal Oscillation (PDO) significantly influences this subduction see‐saw pattern. During PDO warm phases, AL southward shift intensifies the anti‐correlated variations. Conversely, during cold phases, AL northward shift weakens its influence on ESTMW area, resulting in a less stable anti‐phase relationship. Plain Language Summary: Subduction is the process where water from the surface sinks into deeper layers of the ocean. This process is crucial because it moves important elements like heat, carbon, and nutrients from the surface to the depths below. Understanding how subduction changes is essential for elucidating climate change and biogeochemical cycles. Subduction rates in the North Pacific reveal a pattern like see‐saw: when the subduction rate increases in western Subtropical Mode Water (STMW) formation area, it often decreases in eastern STMW formation area. This see‐saw pattern is mainly caused by latent heat flux, through modulation of the late‐winter mixed layer depth. The late‐winter Aleutian Low plays an important role in this process. When it shifts in position or changes intensity, it affects latent heat flux, creating this west–east see‐saw pattern in subduction. Furthermore, this subduction see‐saw pattern is stronger during the warm phase of the Pacific Decadal Oscillation compared to the cold phase. Key Points: North Pacific shows a subduction see‐saw pattern between western and eastern STMW areas, driven by mixed layer depth variationsLate‐winter Aleutian Low activity induces anti‐phase subduction variations through its impact on latent heat fluxPacific Decadal Oscillation modulates the strength of the subduction see‐saw pattern, stronger in warm phases, weaker in cold phases [ABSTRACT FROM AUTHOR]

Analyzing tropical cyclone‐induced remote moisture transport clusters (TRCs) and their effects on precipitation is crucial for understanding precipitation formation and enhancing forecast precision. Prior research, primarily case‐based, did not fully grasp the nature of TRCs. Utilizing an objective TRC identification method, we categorized 65 TRC tracks in East Asia into five types and examined their traits and precipitation links. The findings indicate that the moisture transport height of TRCs varies due to multiple factors, with higher transport linked to the warm conveyor belt and lower transport attributed to Taiwan's mountain range influencing low‐level moisture. The precipitation peak altitudes of TRCs at higher latitudes are greater, and their precipitation intensity is positively correlated with terrain type, especially coastlines. This study underscores the diversity in TRC characteristics and related precipitation, suggesting that future research should consider the directionality of TRC tracks. Plain Language Summary: Examining how water vapor is moved far away by large storms called tropical cyclones (TCs) helps us understand how rain is made and helps us better predict it. Earlier studies did not fully understand what these water vapor clusters, or TRCs, were. Therefore, we used a special method to find and sort TRCs. We identified 65 different paths of TRCs in East Asia and divided them into five different groups. We looked at what makes them different and how they are connected to rain. We discovered that the way that high TRCs move water vapor can change because of many factors. Sometimes, a weather pattern called the warm conveyor belt makes the vapor ascend higher. Other times, the mountains in Taiwan affect the lower part of the vapor. Additionally, TRCs in places that are farther from the equator cause increased amounts of rain, and the amount of rain is closely related to the type of terrain, and this phenomenon is especially prominent near coasts. This study shows that there are many different kinds of TRCs and ways that they affect rain. Future research should also look at the paths that TRCs take. Key Points: TC‐induced remote moisture transport frequently occurs over the Yangtze Plain and eastern oceanTC‐induced remote moisture transport has five main kinds of tracks with different triggering mechanismsThe orientations further affect precipitation through orographic effects and synoptic circulations [ABSTRACT FROM AUTHOR]

Previous studies have highlighted the distinct impacts of anthropogenic aerosols from the Western and Eastern Hemispheres on past multi‐decadal changes in tropical cyclone frequency of occurrence (TCF). However, the detailed effect of subregional aerosol variations remained unclear. Using idealized simulations with a dynamical climate model, this study reveals that reduced aerosol emissions from Europe and the U.S. since 1980 may have equally contributed to increased TCF over the North Atlantic, with Europe playing a major role in the decreased TCF in the South Indian Ocean and the U.S. contributing to the decrease in TCF in the South Pacific. Additionally, increased aerosol emissions from India since 1980 may have played a major role in decreasing TCF over the western North Pacific compared to increased emissions from China. TCFs are projected to decrease for most global tropics toward the end of this century due to the dominant effect of increasing greenhouse gases. Plain Language Summary: Since 1980, human‐made aerosol emissions have decreased in Europe and the U.S. but increased in China and India. This study uses a climate model to explore how regional aerosol changes affect global tropical cyclones. Findings reveal that reduced aerosols from Europe and the U.S. decreased cyclones in the South Indian Ocean and South Pacific, respectively. In contrast, increased aerosols from India decreased tropical cyclones in the western North Pacific more significantly compared to increased aerosols from China. Reduced aerosols from Europe and the U.S. increased tropical cyclones in the North Atlantic to a similar extent. The model projects fewer global cyclones by the end of this century due to rising greenhouse gases, with Europe's and U.S.'s aerosols remaining low and India's increasing. In essence, changing patterns in aerosols and greenhouse gases contribute to shaping the spatial patterns of tropical cyclones. Key Points: Aerosol reductions in Europe and the U.S. may decrease tropical cyclones in the South Indian Ocean and South Pacific, respectivelyElevated aerosols from India since 1980 might notably decrease Western North Pacific tropical cyclonesProjected decreases in frequency of storm occurrence across the tropics due to rising greenhouse gases rather than aerosol changes [ABSTRACT FROM AUTHOR]

A number of recent studies have highlighted how radiative feedback from clouds accelerates tropical cyclone (TC) development by amplifying spatial gradients in radiative heating. This study extends this work by examining how spatial gradients in free tropospheric moisture influence TC development through their impact on environmental radiative heating. We conduct a series of idealized model experiments in which only the longwave radiative heating due to water vapor is modified in the environmental region outside of the TC area. These experiments demonstrate that a vortex in a drier environmental free troposphere experiences faster development. Moreover, weaker vortices actually require a dry environmental free troposphere to develop. The accelerated genesis mainly results from a stronger spatial gradient in moisture‐induced radiative heating, which enhances energy convergence through a stronger transverse circulation. These results highlight a potentially important and overlooked role of dry air in facilitating TC genesis. Plain Language Summary: Recent studies have shown that clouds play an important role in making hurricanes stronger by affecting how heat is distributed. This study builds on that work by looking at how moisture in the environmental air away from the storm center also influences hurricane development through its impact on heat distribution. Computer simulations in which only the heating due to the absorption of infrared heat by water vapor outside the hurricane area was varied showed that hurricanes with drier environmental air develop faster. Further analysis revealed that this faster development is mainly because of a stronger difference in how heat is distributed due to moisture. Our results suggest that dry air might play a crucial and overlooked role in helping hurricanes form. Key Points: Dry environment accelerates tropical cyclone genesis through moisture‐induced gradients in radiative heatingA dry environmental free troposphere enhances the radiative heating gradient between TC area and its surroundingsThe moisture‐induced radiative feedback enhances the energy convergence and is critical to TC genesis in the early stages of development [ABSTRACT FROM AUTHOR]

The rapid development of the wind industry is accompanied by increasing environmental impacts. Currently, there is a lack of research on the impacts of offshore wind farm (OWF) on tropical cyclone (TC) intensity, including the mechanisms involved. This research is carried out by using a coupled and an uncoupled numerical model to investigate the impact of OWF on an autumn TC in the northeastern South China Sea. The results show that the wind speed deficit caused by OWF leads to an increase in surface pressure on the inflow side. This causes the surface pressure in the TC periphery to increase by advection, even if the TC is some distance away from the OWF. The increase in pressure gradient from the periphery to the TC center enhances the TC secondary circulation, thereby intensifying the TC. When the TC enters the OWF, the above mechanisms weaken and the ocean dominates the TC intensification. This is because the reduction in wind speed caused by the OWF results in a weaker sea surface current velocity, which weakens the flow of upstream cold water into the OWF, warming the sea surface temperature (SST) within the OWF. This implies that the horizontal gradient of the local SST is an important factor to be considered in the development of OWF. Sensitivity experiments indicate that OWF can also intensify other types of TC, and that higher cut‐out wind speeds lead to stronger intensification effects. These results also provide a new perspective on TC intensity forecasts. Plain Language Summary: The rapid development of the offshore wind industry has significant impacts on the surrounding environment. There is limited research on the impact of offshore wind farms on the tropical cyclone (TC) intensity. This study indicates that wind farms in the northern South China Sea intensify an autumn TC that makes landfall in China. Wind farms intensify the TC by increasing the surface pressure in the TC periphery when the TC is far from the wind farm. When the TC is close to the wind farm, it is the warming sea water within the wind farm that intensifies the TC. Tropical cyclone can also be slightly intensified when the number of turbines is small. These results help to understand the impact of offshore wind farms on TCs and to improve TC intensity forecasts. Key Points: The tropical cyclone (TC) intensifies before approaching offshore wind farms due to increased peripheral pressure caused by wind farmsThis intensification within wind farms is mainly due to the reduced transport of cold water upstream associated with the wind speed deficitHigher cut‐out wind speeds can lead to a more pronounced intensification of the TC before it enters wind farms [ABSTRACT FROM AUTHOR]

Compound hazards involving tropical cyclones and extreme heat ("TC‐heat") have rarely been examined in prior research. Peripheral subsidence associated with cyclones can warm an area to varying degrees, depending on the cyclone's strength and position. Meanwhile, the peripheral airflow also overwhelmed the land‐sea breeze circulation system in coastal cities and favored downwind urbanized heat advection on the Southern China coastline. Here, we systematically applied ERA5 global reanalysis data, local surface‐level observations, MODIS‐based land‐cover data and HYSPLIT backward trajectories to evaluate how the position of distant TCs may divert the monsoon system and foster the surface heat advection from upwind urban agglomerate amplifying air temperature in downwind coastline. The analysis suggests when a distant TC is situated in a favorable area (the vicinity of Taiwan and Luzon Strait) at roughly 500–1,250 km to the east of Hong Kong, it forms a unique meteorological condition which allows the surface heat transport from the Greater Bay Area to Hong Kong, reflecting that regional build‐up of heat could be an important mechanism for producing local heat extremes. Plain Language Summary: Rapid urbanization and global climate change bring us new hazards through compound extreme weather events in urban society. Tropical cyclones (TC) are known to bring violent wind and heavy rain upon arrival, while in distant they can also send very hot weather conditions (called TC‐heat events) to regions under its subsidence airflow. This study shows the combined effect of heat from upwind urban areas in coincidence with the TC‐induced subsidence could bring even higher temperatures to the downstream cities like Hong Kong. Comprehensive analysis with global climate data, local weather observations, and backward simulation models were used to further understand how the location of TC may adverse the wind circulation patterns in inland areas and contribute to a larger extreme heat threat to the coastal cities. This can facilitate the early forecast and warning for the potential occurrence of such TC‐heat compound hazard, potentially benefitting public preparedness and response in combating extreme heat and cyclone influences. Key Points: High temperature events occur when distant Tropical Cyclone (DistTC) located at 500–1,250 km from Hong KongSurface heat can be built‐up in inland China cities, transport to Hong Kong as downwind footprint and contribute to the temperature enhancementProbability of high temperature events with DistTC is 15% higher than the normal summer days in Hong Kong [ABSTRACT FROM AUTHOR]

Despite the well-known importance of radar data assimilation, there are limited studies on landfalling typhoons in terms of directly assimilating radar reflectivity data, especially using a reflectivity operator based on double-moment microphysics. In this study, radar reflectivity data assimilation experiments are conducted with an ensemble Kalman filter (EnKF), using simulated observations in an Observing System Simulation Experiment (OSSE) framework for the landfalling typhoon In-Fa. With an OSSE, it is convenient to analyze the impact of assimilation of radar reflectivity on analysis and forecast for various state variables, especially for hydrometeors. Our results show that the direct assimilation of radar reflectivity with EnKF does not introduce non-physical hydrometeors and is able to adjust well, not only to hydrometers, but also to some large-scale variables which are not directly related to reflectivity, especially in terms of temperature and vertical velocity. Though the most notable reduction in the Root Mean Square Errors (RMSEs) is observed through mixing the ratio of rainwater and snow, the analysis of other variables is also significantly improved with the accumulation of assimilation cycles. The correlation analysis reveals the strongest correlation between radar reflectivity data and hydrometeor-related variables as well as the correlation with certain large-scale variables, indicating that these cross-variables are updated well through the reliable multivariate ensemble covariance in the EnKF. As a result, an obvious improvement in typhoon intensity and precipitation forecast is obtained in the data assimilation experiment. The impact of assimilation on radar reflectivity can last for up to 15–16 h. [ABSTRACT FROM AUTHOR]

The Constellation Observing System for Meteorology, Ionosphere, and Climate 2 (COSMIC-2) collects data covering latitudes primarily between 40 degrees north and south, providing abundant data for tropical cyclone (TC) research. The radio occultation data provide valuable information on the boundary layer. However, quality control of the data within the boundary layer remains a challenging issue. The aim of this study is to obtain a more accurate COSMIC-2 radio occultation (RO) dataset through quality control (QC) and use this dataset to validate warm core structures and explore the planetary boundary layer (PBL) structures of TCs. In this study, COSMIC-2 data are used to analyze the distribution of the relative local spectral width (LSW) and the confidence parameter characterizing the random error of the bending angle. An LSW less than 20% is set as a data QC threshold, and the warm core and PBL composite structures of TCs at three intensities in the Northwest Pacific Ocean are investigated. We reproduce the warm core intensity and warm core height characteristics of TCs. In the radial direction of the typhoon eyewall, the impact height of the PBL increases from 3.45 km to 4 km, with the tropopause ranging from 160 hPa to 100 hPa. At the bottom of the troposphere, the variations in the positive and negative bias between the RO-detected and background field bending angles correspond well to the PBL heights, and the variations in the positive bias between the RO-detected and background field refractivity reach 14%. This research provides an effective QC method and reveals that the bending angle is sensitive to the PBL height. [ABSTRACT FROM AUTHOR]

High-wind structures were identified in the Cross-Calibrated Multi-Platform (CCMP) ocean wind vector reanalysis for comparison with winds measured by satellite radiometers, scatterometers, and synthetic aperture radar (SAR) instruments from February to October 2023. The comparison aims to evaluate bias, uncertainty, and spatial correlations with the goal of enhancing the accuracy of ocean wind datasets during tropical cyclones (TCs). In 10° longitude × 10° latitude blocks, each containing a TC, Soil Moisture Active Passive (SMAP) and Advanced Microwave Scanning Radiometer 2 (AMSR2) winds are 6.5 and 4.8% higher than CCMP, while Advanced Scatterometer (ASCATB) is 0.8% lower. For extratropical cyclones, AMSR2 and SMAP also show stronger winds with a 5% difference, and ASCATB is about 0.3% weaker compared to CCMP. The comparison between SAR and CCMP for TC winds, sampled at the locations and time frames of SAR tiles, indicates that SAR winds around TCs are about 9% higher than CCMP winds. Using empirically defined TC structural indices, we find that the TCs observed by CCMP are shifted in locations and lack a compact core region. A Random Forest (RF) regressor was applied to TCs in CCMP with corresponding SAR observations, nearly correcting the full magnitude of low bias in CCMP statistically, with a 15 m/s correction in the core region. The hierarchy of importance among the predictors is as follows: CCMP wind speed (62%), distance of SAR pixels to the eye region (21%) and eye center (7%), and distance of CCMP pixels to the eye region (5%) and eye center (5%). [ABSTRACT FROM AUTHOR]

Future changes to the year-to-year swings between active and inactive North Atlantic tropical cyclone (TC) seasons have received little attention, yet may have great societal implications in areas prone to hurricane landfalls. This work investigates past and future changes in North Atlantic TC activity, focusing on interannual variability and evaluating the contributions from anthropogenic forcing. We show that interannual variability of Atlantic TC activity has already increased, evidenced by an increase in the occurrence of both extremely active and inactive TC seasons. TC-resolving general circulation models project a 36% increase in the variance of North Atlantic TC activity, measured by accumulated cyclone energy, by the middle of the 21st century. These changes are the result of increased variability in vertical wind shear and atmospheric stability, in response to enhanced Pacific-to-Atlantic interbasin sea surface temperature variations. Robust anthropogenic-forced intensification in the variability of Atlantic TC activity will continue in the future, with important implications for emergency planning and societal preparedness. [ABSTRACT FROM AUTHOR]

Several damaging tropical cyclones (TCs) have occurred recently over the South Indian Ocean (SIO) region, causing enormous social and economic losses. Yet, while many studies have examined SIO TC characteristics using observations and reanalysis, only a few have assessed these characteristics specifically for this region in climate models, and fewer have investigated their projections under climate change. Here we do this for a historical (1980–2010) and future (2020–2050) period, using multimodel simulations from the High Resolution Model Intercomparison Project, as well as examine biases in the historical period relative to a reanalysis (ERA5). The models have horizontal resolutions of 25–50 km, which has enabled an improved ability to represent tropical cyclones globally in previous studies. TempestExtremes software is employed to detect tropical storm and cyclone tracks. In cases where TempestExtremes cannot be applied due to a lack of requisite variables in a dataset, we instead examine extreme wind speeds in that dataset. For the historical period, we find considerable variation in model biases compared to ERA5, which itself exhibits realistic spatial patterns of tracks and their monthly distribution. Models do at least agree on positive biases in track frequency east of Madagascar and somewhat in the Mozambique Channel. However, the models and ERA5 only produce Category 3 tropical cyclones at best. Wind speeds for 25 km resolution models have much larger positive biases than for 50 km ones, suggesting the former can simulate even higher‐category tropical cyclones. Considerable intermodel variation is also found in track changes between the future and historical periods. No systematic intercategory pattern of change exists, and low signal‐to‐noise may obscure any such patterns in the limited timespan of available data. Thus, no meaningful conclusions can be drawn regarding changes in track intensity. Nevertheless, track frequency broadly decreases across models for the region, as does accumulated cyclone energy. An east‐to‐west shift in track location from east of Madagascar toward the Mozambique Channel is also implied by track frequency and wind speed changes. Our findings provide information to potentially improve storm resiliency in this vulnerable region. [ABSTRACT FROM AUTHOR]

Rainfall in East Asia is affected by two rain‐bearing systems: tropical cyclones and monsoon‐related frontal systems. Distinguishing typhoon rainfall (TR) and non‐typhoon rainfall (non‐TR) helps to understand the evolution process of regional rainfall at different timescales. Taking Fujian Province in the southeast coast of China as an example, based on the fixed box approach of separating TR, the method of determining the size of fixed box is explored. TR and non‐TR are separated in Fujian Province, and the spatial variations of TR and non‐TR at different timescales (annual, monthly, day of annual‐maximum‐rain) are analysed. The results showed that (1) according to the relationship between the sizes of fixed box and the rate of change of TR, the size of fixed box could be reasonably determined; thus, the expended size of fixed box suitable for separating TR in Fujian was 3.5°, namely the range of 20°–31.8°N and 112.3°–124.2°E. (2) The spatial variations of TR at different timescales in Fujian were similar: TR decreased from the coast to the inland, and the northeast coast of Fujian was the high‐value region. Due to the difference of water vapour sources, non‐TR in March–June increased from the coast to the inland, but the high value of non‐TR in July–September was distributed in the eastern coast. (3) The contribution rates of average TR to the total rainfall of the year, July–September and 1 day were 12.8%, 34.6% and 35.7%, respectively. In eastern coast, TR in July–September accounted for 1/3–1/2 of total rainfall, and the rainfall in a day was mainly affected by TR; while in western inland, rainfall was mainly non‐TR and the influence of TR was less than 1/4. [ABSTRACT FROM AUTHOR]

The current study investigates the modulation of the tropical cyclone (TC) frequency (TCF) over the Bay of Bengal (BoB) by the southern annular mode (SAM). The analysis reveals that the SAM–TCF relationship during October–November–December has undergone interdecadal changes from significant during 1971–1994 to insignificant during 1995–2021. This contrasting influence of the SAM on the TCF occurrence is also echoed in the large‐scale environmental variables conducive to forming tropical cyclones (TCs). Based on the possible mechanism, we found that the SAM can imprint tripole sea surface temperature (SST) patterns in the southern Indian Ocean via altering surface wind speed from 1971 to 1994. The SAM‐related tripole SST pattern induces the surface‐level anticyclone anomaly, which enhances the south easterlies towards the western equatorial Indian Ocean. Such intensified anomalous wind crosses the equator and diverts towards the east to form the cyclone anomaly in the BoB. Meanwhile, at 200 hPa, the anomalous anticyclone over western Australia induces divergent wind flows over the study region. Consequently, the ascending motion in BoB promotes the tropical cyclone generation. During 1995–2021, however, the SAM is associated with the dipole SST pattern in the southern Indian Ocean. Correspondingly, the SAM‐related dipole SST yields anomalous atmospheric circulations confined to the Southern Hemisphere and eventually fails to impact the formation of TCs in the northern Indian Ocean, where the study region is located. The findings of this research can be useful in advancing our knowledge of the interannual variability of TCs activity in the BoB based on the remote climate signal. [ABSTRACT FROM AUTHOR]

Westerly wind bursts (WWBs) in the western–central equatorial Pacific are critical in El Niño–Southern Oscillation (ENSO) dynamics. Understanding how they may change with global warming has important implications for future projections of El Niño. In this study, we investigate how the enhanced eastern equatorial Pacific warming pattern, emerging in future climate projections, can influence WWB characteristics in an atmospheric general circulation model, CAM6. Changes in three main factors affecting WWBs—El Niño-conditions mean westerly wind stress anomalies, the Madden–Julian oscillation (MJO), and tropical cyclones (TCs)—are analyzed. We find that during El Niño onset (December–April), the WWB wind stress intensity remains largely unchanged but WWBs shift westward by about 20° of longitude. In contrast, during El Niño development (May–November), the WWB intensity increases by 41% or 79% in two warming scenarios considered [shared socioeconomic pathways (SSP5-8.5) and SSP2-4.5, respectively], which is mainly caused by a higher frequency of TC occurrence in the central tropical Pacific within 15°N/S. Further, we find that westerly wind speed anomalies associated with El Niño and the MJO also increase during El Niño development. However, as trade winds weaken in the central-eastern equatorial Pacific, the mean strength of the resulting westerly wind stress anomalies does not change much, and no significant eastward shift of WWBs is observed. Thus, our atmospheric model simulations suggest a strong TC-driven increase in WWB wind stress anomalies during El Niño development and hence a more important role of TCs in WWB generation, which in a coupled system could lead to stronger ENSO events, enhanced TC–ENSO coupling, and even greater intensification of WWBs. [ABSTRACT FROM AUTHOR]

To gain a scientific understanding of the cross-system impact of coastal zones and promote the sustainable development and protection of coastal areas, we constructed a spatial benefit evaluation system that encompassed both terrestrial and marine systems, focusing on the ecological, economic, and social dimensions. We employed the entropy method, moving average method, and Mann-Kendall trend test to quantitatively characterize the spatial benefits of the coastal zone in Fujian Province, China, and the evolution of the marine climate from 2005 to 2020. Building on this, the grey relational analysis method was applied to investigate the correlation between spatial benefits and marine climate and to explore the trends and magnitude of the impact of marine climate on spatial benefits. During the study period, the spatial benefits of the coastal zone in Fujian Province exhibited a fluctuating pattern of an initial increase followed by a decrease, with spatial benefits varying among cities. The role of the economic system in enhancing spatial benefits was not considerable. Changes in the marine climate aligned with the global warming trend, with the most considerable changes observed in sea level and tropical cyclone frequency and intensity, which are sensitive to human activities. There was a high degree of correlation between coastal zone spatial benefits and marine climate, with seawater salinity being most closely related to spatial benefits, while tropical cyclones showed the weakest correlation. The results of this study support sustainable development efforts in coastal zones. [ABSTRACT FROM AUTHOR]

The increasing climate-change-induced tropical cyclone phenomena expose the power grid to significant operation risks by disrupting the normal operation of grid components. This paper considers the failure mechanism with respect to critical grid components and reveals a novel spatiotemporal revolution of grid failures during the passage of typhoons. Based on the spatiotemporal evolution of grid failures, a threshold-based emergency scenario set and the corresponding two-stage robust optimization-based emergency dispatch model are developed. The robust emergency dispatch strategy is obtained using a column-and-constraint generation (C&CG) algorithm. The simulation results show that the proposed robust emergency dispatch strategy can guarantee a considerable degree of robustness under multiple emergency scenarios driven by uncertain typhoon conditions. [ABSTRACT FROM AUTHOR]

Introduction: The Dominican Republic, due to its nature as a Small Island Developing State (SIDS), faces several challenges in the face of extreme weather phenomena such as hurricanes. Therefore, integrating technologies such as Augmented Reality (AR) in teaching these topics in class can influence student motivation and improve learning. Aim: This article has three objectives: 1) to evaluate the learning results of the participating students using the pre-test and post-test methodology; 2) to find out the cognitive load it produces in the participating students and 3) to analyze the relationships between the different types of cognitive load. Methodology: It has a quantitative approach, with a quasi-experimental design using the pre-test-post-test technique. It was carried out between May and July 2024 and consists of a non-probabilistic sample (N = 45). In addition, the student's cognitive load was measured when interacting with the AR object, in its three types: internal, external, and relevant. Results: When comparing the results of the pre-test and post-test, we obtained average values of 3.84 with a high level of variability and 4.75, with less dispersion in the answers. On the other hand, the cognitive load instrument shows high levels of internal consistency with 0.93 for the total instrument. The strongest correlation, 0.93, was obtained between external cognitive load and mental effort invested. Conclusions: The hypothesis has been tested: participating students have better learning outcomes about hurricanes (tropical cyclones) after interacting with the learning object in AR format. [ABSTRACT FROM AUTHOR]

This study examines the influence of NASA Cyclone Global Navigation Satellite System (CyGNSS) Level 2-derived 10 m (near-surface) wind speed over the ocean on analyses and forecasts within the NOAA operational Hurricane Analysis and Forecast System (HAFS). HAFS is coupled with a regional configuration of the HYCOM ocean model. The primary advantages of data from the CyGNSS constellation of satellites include higher revisit frequency compared to polar-orbiting satellites, and the availability of reliable wind observations over the ocean surface during convective precipitation. CyGNSS data are available early in the life cycle of tropical cyclones (TCs) when aerial reconnaissance observations are not available. We focus on TCs whose forecasts were initialized when the TC was a depression or tropical storm. In the present study, we find first, that assimilation of CyGNSS near-surface winds improves storm track, intensity, and structure statistics in the analysis and early in the forecast, for many cases. Second, we find that assimilation of CyGNSS observations provides additional insights into the evolution of air-sea interaction in intensifying TCs: In effect, the ocean responds in the coupled model to modifications in the initial 10 m wind field, thereby impacting forecasts of intensity, storm structure, and sea surface height, as demonstrated by two case studies. We also discuss some forecasts where assimilating CYGNSS appears to degrade performance for either intensity or structure. [ABSTRACT FROM AUTHOR]

Tropical cyclone forecasting relies on accurate sea surface temperature, yet the errors in available sea surface temperature products remain unclear. Here, I evaluate the sea surface temperature errors under tropical cyclones in the western North Pacific based on surface drifters across eight widely-used datasets, including satellite, atmospheric and oceanic analysis-or-reanalysis products, spanning from 2014 to 2023. The ensemble mean bias and root-mean-squared-error are firstly quantified. Both satellite and oceanic analysis sea surface temperatures exhibit a cold bias, while atmospheric analysis-or-reanalysis sea surface temperature shows a warm bias. Specifically, atmospheric analysis-or-reanalysis products consistently show a warm bias in the right-rear quadrant of the tropical cyclone coordinate system. Regarding root-mean-squared-error, for most products, the right side consistently exhibits higher errors than the left side. SST bias significantly impacts tropical cyclone intensity change as indicated by empirical relationship. These results provide direct insights for operational tropical cyclone forecasting and research. [ABSTRACT FROM AUTHOR]

This study aimed to comprehend the effects of Typhoon Maria on the pelagic ecosystem in the southern East China Sea. Shipboard measurements were conducted at eight sampling stations before (2–4 d) and after (3–6 d) the typhoon, which enabled the evaluation of the potential impacts of the typhoon on this pelagic ecosystem, with particular focus on carbon dynamics. Following the typhoon's passage, there was a slight drop in sea surface temperature. The response of the variables to the typhoon, however, exhibited variations at different sampling stations. For further analysis, t‐tests compared variables, while type II regression assessed the linear correlation between two variables. Overall, during the post‐typhoon period, concentrations of nitrate, chlorophyll a, primary production, bacterial biomass and production, plankton community respiration, and abundance of large phytoplankton (> 2 μm) and the relative abundance of picophytoplankton among larger‐sized picoeukaryotes were higher compared to the pre‐typhoon period. The mean value of fugacity of CO2 was similar to or slightly lower than pre‐typhoon period. Although the typhoon‐induced vigorous primary production might have absorbed a significant amount of CO2, the decrease in fugacity of CO2 could have been offset by the plankton community respiration. The findings suggest that the typhoon enhanced physical disturbance and increased water column mixing, which, in turn, augmented nutrient availability and promoted plankton growth in the shallow water column. Overall, this study sheds light on the complex interactions between typhoons and marine ecosystems and highlights the importance of further investigating these phenomena to better understand their ecological implications. [ABSTRACT FROM AUTHOR]