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The study investigates the rapid intensification (RI) of tropical cyclones (TCs) in the Northwestern Pacific. We found that rapid changes in the maximum wind speed (Vmax) and the minimum central pressure (Pmin) are not always concurrent. RI cases can be categorized into three types: (a) RIv, only Vmax strengthens rapidly; (b) RIp, only Pmin decreases rapidly; (c) RIpv, rapid changes in Vmax and Pmin occur concurrently. At the onset of RI, RIv‐type TCs exhibit the weakest intensity and the smallest size, with deep convection concentrated in the inner‐core region; RIp‐type TCs are characterized by the strongest cyclone intensity and the largest outer‐core size, with strong convection covering the inner‐ and outer‐core regions; RIpv‐type TCs show moderate intensity, size, and convection distribution. For RIpv, significant strengthening of wind profile is concentrated in the inner‐core region, while for RIp it is more prominent in the outer‐core. Plain Language Summary: The rapid intensification (RI) of tropical cyclones (TCs) continues to pose challenges in both operational forecasting and scientific research. The maximum wind speed (Vmax) and the minimum central pressure (Pmin) are two commonly used TC intensity indicators. In most of existing studies, one single indicator (usually Vmax) is used to investigate the RI process. Whether there is a difference between RI cases defined by 24‐hr strengthening of Vmax and 24‐hr deepening of Pmin is an issue deserving discussion. The study found that rapid changes in Vmax and Pmin are not always concurrent. In the cases where only Vmax strengthens rapidly, the outer‐core size of TC expands slowly. While in the cases where only Pmin deepens rapidly, the enhancement of outer circulation is distinctive. Since the Pmin, as an integral variable, reflects TC information of both the intensity and the size, RI cases classified via these two commonly used indicators (Vmax and Pmin) could help us further understand the relationship between TC intensity and size. Key Points: Rapid changes in the maximum wind speed (Vmax) and the minimum central pressure (Pmin) are not always concurrent in tropical cyclones (TCs)TCs that only experience a rapid increase in Vmax (RIv) tend to have a significantly weaker lifetime maximum intensityThe evident expansion of the outer circulation occurs in TCs of which only Pmin deepens rapidly (RIp) [ABSTRACT FROM AUTHOR]

This study aimed to explore the predictability of the most long‐lived tropical cyclone (TC) Freddy in 2023 while it traversed westward across the southern tropical Indian Ocean during the first 18 days of its existence. Global ensemble forecasts revealed southward track deflection and intensity underestimation of Freddy. We identified three key factors contributing to the limited predictability of Freddy, which are associated with the Mascarene High, Storm Dingani, and Freddy itself. The large track errors of Freddy can be attributed to the underestimated strength of the Mascarene High, the more northeastern position of Dingani, and the presence of excessively large or small sizes of Freddy. These findings were further validated through a high‐resolution regional model. Specifically, Freddy's track and intensity most closely matched the observations when these three factors were most closely represented. It underscores the pivotal role played by the interaction between TCs and multi‐scale systems in TC forecasts. Plain Language Summary: In 2023, Storm Freddy emerged as the most long‐lived tropical cyclone (TC) in record, lasting 35 days over the southern tropical Indian Ocean and spanning both weather and sub‐seasonal to seasonal time ranges. The primary objective of this study is to understand the factors contributing to the poor predictability of Freddy in forecasts spanning over 2 weeks. This holds significant importance as our understanding about the ability of the numerical models to predict long‐lived TCs remains limited. Using over 7,000 global ensemble forecasts from five global Numerical Weather Prediction (NWP) centers and a high‐resolution regional model, we identified three key factors contributing to the limited predictability of Freddy: the strength of the Mascarene High, the position of Storm Dingani (2023), and the size of Freddy. In large track‐error results of the global forecasts and regional simulations for Freddy, the strength of the Mascarene High was underestimated, Dingani was located further northeast, and Freddy was either too large or too small. Our investigation emphasizes the crucial role played by the interaction between the TC and multi‐scale systems in TC forecasts. This is meaningful for the improvement of Numerical Weather Prediction models to deal with extreme TC events in the future. Key Points: Due to the long lifespan of Storm Freddy, many forecasting challenges across several numerical models aroseThe limited predictability of Freddy was related to the underestimated Mascarene High and the more northeastern position of Storm DinganiThe inaccurately forecasted size of Freddy, whether excessively large or small, also contributed to the large track errors [ABSTRACT FROM AUTHOR]

This study investigates the evolution of tropopause layer cooling (TLC) in an idealized tropical cyclone (TC) as well as the physical mechanism for its formation throughout its lifetime. TLC development is closely related to the intensity change of the TC. The TLC within the inner core of a TC coincides with the occurrence of the TC warm core, whereas the enhancement of the TLC precedes the strengthening of the warm core and the intensification of the TC. This phenomenon suggests that the TLC could be a valuable signal for predicting TC intensity and intensity change. After the onset of rapid intensification, the TLC continues to enhance until it is replaced by the warm core in the inner core region, and it expands to the outer core area and forms a cold ring above the TC outflow layer. The budget analyses of the azimuthal mean potential temperature indicate that advection plays a leading role during all stages of the TLC evolution. Prior to and during the rapid intensification stages of a TC, advection (due to eddy motion) contributes to a cooling of the upper layer above the TC center. This upper‐level cooling is assumed to be related to the uplift caused by overshooting and convection within the inner core. However, the advection process caused by the azimuthal vertical motion dominated the broad cooling across the whole TLC area. Plain Language Summary: Observations and numerical simulations show that there is typically a cold anomaly above the TC warm core. This cooling can work with the warm core to reduce the upper‐tropospheric stability and affect the water vapor and momentum transport between the TC and the stratosphere. However, little is known about how the cold anomaly evolves during the life cycle of a TC and how it can be related to changes in TC intensity. This study examines the evolution of the cold anomaly throughout the lifetime of a TC with an idealized TC simulation. The cold anomaly emerges at the TC center before rapid intensification starts and continues to enhance during TC development. It moves radially and forms a cold ring around the TC until the mature stage. The advection, specifically the vertical mean motion, dominates the generation of the TLC, but the advection due to eddy motions is responsible for the cold anomaly near the center. Our findings demonstrate the importance of tropopause layer cooling on TC structure and intensity changes and indicate the necessity of additional observations of this cold anomaly to improve TC predictions. Key Points: The cooling tendency in the tropopause layer enhances continuously during the preintensification and rapid intensification stages of tropical cyclone (TC)The adiabatic uplift caused by overshooting convection can cool the upper layer in the TC center through azimuthal‐eddy advectionThe broad ring of the cold anomaly above the TC outflow layer is related to adiabatic cooling through the azimuthal mean vertical motion [ABSTRACT FROM AUTHOR]

The prediction of tropical cyclone (TC) intensity remains a major scientific challenge. Recent studies indicate that cloud‐radiation feedback (CRF) plays a positive role in the intensification of TCs during their genesis. However, little attention has been given to how CRF affects TC intensity after genesis. This study shows that CRF may prevents TCs from attaining higher maximum intensities. The ascending motion induced by the anomalous radiative heating of TC promotes more latent heating on the outer side of the upper eyewall, resulting in a more tilted eyewall. A more tilted eyewall leads to a larger inner‐core size and less inward flux of absolute vertical vorticity within the inner core, thus preventing the TC from reaching higher intensity. This work highlights that CRF may affect TC intensity by modulating the structure of the inner‐core convection, and further advances our understanding of the interaction between radiation effect and TC dynamics. Plain Language Summary: Cloud‐radiation feedback plays an important role throughout the life cycle of a tropical cyclone (TC). While many previous studies have focused on the effects of cloud‐radiation feedback (CRF) during TC genesis, little work has examined how CRF modulates TC intensity after TC genesis. With idealized simulations, this study shows that radiation‐induced secondary circulation leads to a more tilted eyewall, which results in a larger inner‐core size and less inward flux of absolute vertical vorticity, finally preventing TCs from reaching higher intensities. These results demonstrate that after TC genesis, CRF may affect storm intensity by modulating the structure of the inner‐core convection, a pathway previously overlooked. This study also reveals, counterintuitively, that CRF may have opposite effects on TC intensities at different stages of their lifetimes. Key Points: Cloud‐radiation feedback (CRF) results in a larger but weaker tropical cyclone (TC)Anomalous radiative heating induces a more tilted eyewall, leading to a larger radius of the maximum wind and less inward flux of vorticityThe effect of CRF on TC inner‐core processes is critical [ABSTRACT FROM AUTHOR]