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Drought is a slow onset, recurring and inevitable feature of South Africa's climate. This research deconstructs the meteorological processes underlying drought and its impacts on surface temperature and vegetation in the more productive eastern half of South Africa. We use an index area 22–31°S, 22–32°E and extract monthly satellite and reanalysis data in the period 1979–2019. Drought intensity is determined by i) vegetation color, ii) soil moisture, iii) maximum air temperature and iv) net outgoing longwave radiation. Global drivers are represented by tropical Pacific and Indian Ocean sea temperatures. Composite and regression analysis of drought reveals a mid-tropospheric anticyclone over Namibia induces equatorward flow and subsidence that drives away atmospheric moisture. This feature is associated with the Pacific El Nino, positive Indian Ocean Dipole and an accelerated westerly jet stream. Ocean warming east of Madagascar draws NW-cloud bands there. The advection of anticyclonic vorticity from the South Atlantic and standing atmospheric Rossby wave-trains are key features of South African drought. Dry spells in the summers of 2015, 2016 and 2019 were more intense than 1983 and 1992, as reflected by S-pan potential evaporation measurements >14 mm/day. Despite water deficits, maize yields and river discharge appear stable, due to the uptake of scientific advice and innovative engineering.

This study considers how the Madden Julian Oscillation (MJO) reaches the Caribbean using observational ~ 20-–80-day filtered data in the period 1998–2015. MJO’s presence is quantified by reanalysis zonal wind shear (200 minus 850 hPa) and satellite outgoing longwave radiation (OLR) in a receipt area 10–15 N, 60–80 W and in a transmission area of the equatorial east Pacific 2 S–7 N, 110–130 W. Lag correlations between these two zones, one near the cold tongue and another downstream and off the equator, indicate that the main season for MJO transmission is September to November, when Caribbean sea surface temperatures exceed 28 °C and the equatorial trough lies northward. The MJO portion of total variance is 16 to 20% for daily OLR and zonal wind shear, respectively. MJO signal propagation from Pacific to Caribbean in September–November is ~ 10 m/s. As the transient zonal overturning circulation approaches (− 10 days), there is enhanced convection in the Caribbean. After passage, there is an even stronger suppressed convection signal (+ 10 days). The MJO-air pressure correlation map exhibits a dipole pattern in the east Pacific (0 N, 90 W) and Caribbean (20 N, 80 W), the later sweeping eastward while the former stays west of the Andes where upwelling and low clouds are frequent. Moist westerly surges accelerate near Colombia and are drawn into passing tropical cyclones in two cases: Ivan September 2004 and Sandy October 2012.

Climate predictions using recent and high-resolution climate models are becoming important for effective decision-making and for designing appropriate climate change adaptation and mitigation strategies. Due to highly variable climate and data scarcity of the upper Blue Nile Basin, previous studies did not detect specific unified trends. This study discusses, the past and future climate projections under CMIP6-SSPs scenarios for the basin. For the models’ validation and selection, reanalysis data were used after comparing with area-averaged ground observational data. Quantile mapping systematic bias correction and Mann–Kendall trend test were applied to evaluate the trends of selected CMIP6 models during the 21st century. Results revealed that, ERA5 for temperature and GPCC for precipitation have best agreement with the basin observational data, MRI-ESM2-0 for temperature and BCC-CSM-2MR for precipitation were selected based on their highest performance. The MRI-ESM2-0 mean annual maximum temperature for the near (long)-term period shows an increase of 1.1 (1.5) °C, 1.3 (2.2) °C, 1.2 (2.8) °C, and 1.5 (3.8) °C under the four SSPs. On the other hand, the BCC-CSM-2MR precipitation projections show slightly (statistically insignificant) increasing trend for the near (long)-term periods by 5.9 (6.1)%, 12.8 (13.7)%, 9.5 (9.1)%, and 17.1(17.7)% under four SSPs scenarios.

Near-surface winds around the mountainous Caribbean islands contribute to orographic lifting and thermal diurnal rainfall that requires mesoscale analysis. Here, a new perspective is presented via high-resolution satellite and reanalysis products. Singular value decomposition is applied to 5 km cold-cloud duration satellite data to understand the leading mode of seasonal hydro-climate variability and its regional controls. The spatial loadings reflect wet islands in a dry marine climate, while temporal amplitude is modulated by the large-scale zonal circulation. When summer-time trade winds weaken, daytime confluence around Caribbean islands enlarges, gathering and lifting more moisture. In addition to the static geographic forcing, transient easterly waves impart the majority of marine rainfall between June and September. Higher resolution products capture the thermal orographic effect and reveal upward trends in island rainfall and soil moisture over the satellite era, while lower resolution products miss this effect. The climate of mountainous Caribbean islands is trending toward increased runoff and soil moisture.

Climatic trends in observed and reanalysis data 1980–2014 are mapped to describe spatial structure in the central Caribbean and for guidance on future conditions. Surface air temperatures averaged over the study area 16–22°N, 80–68°W exhibit trends of + .02°C/year, that relate to radiative forcing by greenhouse gases and changes in atmospheric subsidence. Rainfall trends for the Antilles Islands are weakly upward around the Windward Passage 18–20.5°N, 78–73°W and downward to the east 18–20°N, 72–68°W. Spatial trends in air temperatures exhibit a steeper increase over the islands and away from the Windward Passage. Trends in satellite vegetation fraction are upward along the coast and coincide with rising latent heat flux especially west of Hispaniola. An accelerating Hadley circulation exhibits subsidence, warming and drying above 850 hPa. Near the surface, there is a trend of northeasterly winds channeled through the Windward Passage and increased moisture benefiting shallow convection. The research uncovers mesoscale structure in climate change through interaction of wind and rainfall trends.

The study describes northward excursions of the ITCZ across the inter-Americas during boreal summer, using observational datasets at multi-year, annual and daily time-scales. The annual cycle is felt across the region via evenly distributed SST warming in the summer hemisphere. Low-level air is propelled northward from June to October by the southern Hadley cell. Discharges from the Amazon and Orinoco Rivers spread into the Atlantic Ocean at that time of year. A N–S dipole pattern in satellite outgoing longwave radiation (OLR) is calculated and its temporal character reveals northward ITCZ excursions at 4–6 years period corresponding with a warm east Pacific and intensified diabatic heating near Panama. Composite analysis reveals evidence of a standing atmospheric Rossby wave pattern embedded in westerly flow anomalies which bifurcate on passing the Andes and slant across the inter-Americas in Jun–Oct season: lowering SLP and energizing Caribbean hurricanes. Variability at intra-seasonal time scale is underpinned by the southern jet stream and a ridge over Brazil that pushes the ITCZ northward, as seen in statistical regression and case study analysis of satellite OLR and NCEP2 reanalysis fields. The southern Hadley cell plays a prominent role, transmitting signals from winter to summer hemisphere at all time scales.

This study describes how climatic conditions affect of the generation and transport of dust over the SW Sahara Desert (12°-22°N, 18°W-20°E), with a focus on early summer in the period 1980–2014. Results are given for the annual cycle and climatology of May–Aug season, trends in aerosol optical depth (AOD) and contributing factors, co-variability of monthly and daily AOD and climate variables, case studies of dust generation in early summer and analysis of diurnal fluxes. The study is underpinned by multi-satellite measured AOD and ECMWF meteorological reanalysis fields. Linear trends in the period 1980–2014 indicate that AOD (dust) diminished slightly as rainfall and vegetation cover increased. Concommitant climatic trends include a weakening of Atlantic trade winds, acceleration of the easterly jet and inland penetration of the Guinea monsoon. Trends in temperature and winds strengthen above the boundary layer; suggesting that surface changes are damped by greening of the Sahel 1980–2014. Climatic conditions favoring dust emissions are evident in sensible heat flux, maximum temperature and upward motion at seasonal and daily time scales, with influence from wind vorticity at diurnal time scale. Incremental knowledge on climatic controls of dust mobilization could improve emission budgets and forecasts for the SW Sahara Desert.

Jury, M.R., 2018. Characteristics and meteorology of Atlantic swells reaching the Caribbean. The characteristics of Atlantic swells reaching the Caribbean (19° N, 66° W) are described using wave hindcast and buoy datasets. The methods include calculation of histograms, scatterplots, temporal trends, ranking of extremes, meteorological case analysis, comparison of alternative datasets, and an assessment of similarity between cases. Northerly swells occur 29% of the time, with a mean height and period of 2 m and 8 seconds. A slight upward trend in wave period during 1998–2013 was related to an expanding anticyclonic Hadley circulation in the northwest Atlantic. An extreme case analysis illustrates how a storm near Bermuda on 16–20 March 2008 intensified as high pressure near Greenland blocked its progression. The cold air outbreak from the storm and 20 m/s northerly wind gusts induced heat fluxes up to 1000 W/m2 over the Gulf Stream outflow. Swells >6 m traveled southward, attenuating to 4–5 m and ...

Regional factors modulating eastern Venezuela coastal upwelling emerge from this observational study. Trade winds of 3–9 m/s are a persistent feature of the shelf zone, and drive offshore Ekman transport and pumping, cooling SST by 1–3 °C especially in spring. Wavelet spectral analysis of SST anomalies (11oN, 65oW) show significant intra-seasonal (9, ∼ 45, ∼ 100 days) and inter-annual oscillations ( ∼ 3, 9 years). A case study upwelling event of 3–5 May 2014 is distinguished by a low level wind jet on the shelf edge. An ocean eddy propagated westward along the shelf, initially suppressing then enhancing offshore transport. Venezuela SST variability reflects atmospheric control by the North Atlantic anticyclone and associated trade wind-driven shelf water transport and regional evaporation. Eastern Venezuela coastal upwelling involves an atmospheric meridional overturning circulation that affects the frequency of Caribbean hurricanes.

This study analyzes warm spells in the dry season over the East African plateau. Lake levels were observed to decline in the period July 2004 to January 2007. The warmest spell was identified using maximum temperature and satellite outgoing longwave radiation (OLR) observations averaged over Uganda: 20–22 Feb 2005. Meteorological conditions in that case were dominated by a surge of the NE monsoon from the Arabian Sea toward East Africa. Subsiding air induced daytime land surface temperatures >55 °C. Dry easterly winds swept across Uganda, and the vegetation fraction dropped >10% in 1 month. At the seasonal scale, the NE monsoon intensity over the Arabian Sea correlated with indices of desiccation over the White Nile basin. In the annual cycle, sensible heat flux follows potential evaporation, reaching −4.5 mm/day in February. Coupled Model Intercomparison Project Phase 5 (CMIP5) model projections favor a long-term weakening of the NE monsoon and a northward migration of the equatorial trough over the west Indian Ocean in Dec–Mar season. Although maximum temperatures are projected to rise +2 °C by the end of the 21st century, the length of the dry season could shrink, thus maintaining the water balance near current levels.

Climatic trends in the southeastern Antilles island chain are analysed via reanalysis datasets in the period 1980–2014. Although a homogeneous marine climate surrounds these small islands embedded in northeast trade winds, the analysis presented here reveals spatial gradients in climatic trends during the satellite era. In the axis of the fresh North Brazil Current, sea surface temperature (SST) trends are steep (+0.04 °C year−1) and correspond with weaker winds and rising ozone concentrations (+0.15 DU year−1). Subsidence and meridional wind trends are related to an acceleration in the Hadley overturning atmospheric circulation which heats the trade wind inversion. Expanded wind shadows induce warmer SST, greater latent heat flux and deeper convection west of the Antilles islands. While rainfall has decreased in Trinidad and eastern Venezuela, the mountainous islands of Guadeloupe, Dominica and Martinique have increasing rainfall (+0.02 mm day−1 year−1) in the satellite era. Weakening ocean currents near Grenada may reflect a diminishing of the global thermohaline meridional overturning circulation.

The meteorological conditions associated with air pollution episodes on South Africa’s Highveld were studied using Ozone Monitoring Instrument (OMI) and Atmospheric Infrared Sounder (AIRS) satellite estimates, MERRA2 reanalysis model products, and in situ weather data. Surface-layer sulfur dioxide (SO2) and nitrogen dioxide (NO2) display high concentrations during winter (May–July) and provide a focus for statistical analysis of monthly and daily time series. Highveld area-averaged monthly model SO2 was temporally correlated with boundary layer height (correlation coefficient of −0.76) and temperature lapse rate (+0.65) for the period of 1980–2015, but relationships with winds were weak. Daily Highveld area-averaged satellite NO2 was related to dewpoint temperature (−0.59) and exhibited pulsing in the range of 7–24 days for 2005–15. High concentrations of these short-lived locally generated air pollutants were found over and southeast of Johannesburg as a result of urban and industrial emissions. The spatial regression of daily NO2 onto regional sea level air pressure fields for May–July over 2005–15 revealed the slow eastward movement of an anticyclone. At the climatic time scale, Pacific Ocean La Niña conditions favored an increase of May–July SO2 concentrations when sea surface temperatures in the equatorial Atlantic Ocean were warmer than normal. The meteorological pattern underlying the highest-ranked air pollution event of 18–25 July 2008 was characterized by sharp anticyclonic curvature of low-level winds that induce subsidence and consequently a stable lapse rate and low dewpoint temperature (−5°C). The wind vorticity exerted a stronger influence on dispersion than did the surface divergence. This new understanding will underpin better air-quality forecasts over the South African Highveld.

This study analyzes large-scale controls on Uganda’s rainfall. Unlike past work, here, a May–October season is used because of the year-round nature of agricultural production, vegetation sensitivity to rainfall, and disease transmission. The Uganda rainfall record exhibits steady oscillations of ∼3 and 6 years over 1950–2013. Correlation maps at two-season lead time resolve the subtropical ridge over global oceans as an important feature. Multi-variate environmental predictors include Dec–May south Indian Ocean sea surface temperature, east African upper zonal wind, and South Atlantic wind streamfunction, providing a 33% fit to May–Oct rainfall time series. Composite analysis indicates that cool-phase El Nino Southern Oscillation supports increased May–Oct Uganda rainfall via a zonal overturning lower westerly/upper easterly atmospheric circulation. Sea temperature anomalies are positive in the east Atlantic and negative in the west Indian Ocean in respect of wet seasons. The northern Hadley Cell plays a role in limiting the northward march of the equatorial trough from May to October. An analysis of early season floods found that moist inflow from the west Indian Ocean converges over Uganda, generating diurnal thunderstorm clusters that drift southwestward producing high runoff.

This study explores the thermodynamic and kinematic features of easterly waves over northeast Africa in July–September season 2005–2015. A daily African easterly wave (AEW) index is formulated from transient satellite rainfall and reanalysis vorticity, and the ten most intense cases are studied by composite analysis. Surface moisture is advected from central Africa towards the Red Sea during AEW formation. The anomalous 600 hPa wind circulation is comprized of a cyclonic-south anticyclonic-north rotor pair and accentuated easterly jet along 17N. Composite convection is initiated over Ethiopia and subsequently intensifies following interaction with a zonal circulation located downstream. Composite AEW temperature anomalies reveal a cool lower–warm upper layer heating profile. 2–8 day variance of satellite OLR reaches a maximum over the southern Arabian Peninsula, suggesting an upstream role for surface heating and the Somali Jet. The large scale environment is analyzed by regression of the AEW index onto daily fields of rainfall, surface air pressure and temperature in July–September season (N = 1004). The rainfall regression reflects a westward propagating AEW wave-train of higher values on 13N and lower values on 7N with a longitude spacing of ~25°. The air pressure and temperature regression features a N–S dipole indicating an anomalous northward ITCZ. A low pressure signal west of the Maritime Continent coupled with a warm zone across the South Indian Ocean coincides with AEW formation over the eastern Sahel.

Jury, M.R., 2017. Multiple drivers of intense coastal upwelling at Cape Town. Cape Town, South Africa is well known for its intense coastal upwelling during austral summer. This study provides new insights using daily 4–9 km resolution satellite and ocean reanalysis datasets in the period 2009–2015. A key purpose of this work is to highlight the value of these finely detailed products in coastal research. The most intense case of 23–24 January 2011 revealed a cold plume

Environmental influences on Hurricane Maria in the Antilles Islands are analyzed at the large-scale (1&ndash, 25 September) and at the meso-scale (17&ndash, 20 September 2017). The storm intensified rapidly prior to landfall in Dominica, going from category 1 to 5 in 15 h. As the storm progressed toward Puerto Rico (PR), its NE flank entrained air from seas cooled by the earlier passage of two hurricanes, and strengthened on its SW flank. Operational model forecasts tended to delay intensification until west of the Antilles Islands, thus motivating two independent weather research and forecasting (WRF) simulations. These gave minimal track errors at 1- to 3-day lead time. The simulation for landfall at Dominica on 19 September 2017 showed that a static nest with 0.8 km resolution using a Holland-type synthetic vortex and Yonsei University (YSU)/Kain-Fritsch schemes performed better, with a track error of 8 km and intensity error of 10 m/s. Our PR-area simulation of central pressure lagged 30 hPa behind observation, and caught up with reality by landfall in PR. The simulated rainband structure corresponded with Cloudsat observations over PR. Maria&rsquo, s intensification occurred in an area of thermodynamic gradients included cooler SST in the right side of the track, so operational models with right-track bias were late in predicting intensification. Category-2 forecasts prior to 18 September 2017 left many Antilles islanders unprepared for the disaster that ensued.

International audience

Cape Frio at the Angola-Namibia border, is the northern-most coastal upwelling cell of the Benguela Current (~17S, 11E) and is sensitive to climate variability. This study provides new insights using daily high resolution satellite and ocean-atmosphere reanalysis datasets in the period 1985–2015. The annual cycle of SST follows two months behind the net heat balance and wind stress curl, reaching a minimum in July–September. Ranking the daily SST record, two intense multi-day upwelling events stand out. The more recent case of 26–29 August 2005 is studied, given the greater density and sophistication of satellite data. A coastal wind jet >10 m s−1 develops next to Cape Frio, with sharp edges imposed by a thermal inversion and the mountainous cape. The cold plume

The bi-modal climate of SE Ethiopia shares attributes with East Africa, notably that El Nino enhances rainfall, particularly in Sep–Nov season. In this study SE Ethiopia’s continuous and seasonal rainfall relationships to global climate are studied to extend our knowledge of its determinants and predictability. A statistical forecast algorithm for the Sep–Nov short rains accounts for 54% of variance in 1980–2010. The Apr–Jun predictors include South Atlantic sea surface temperature, east Indian Ocean sea level air pressure and China upper zonal wind. Cooling in the South Atlantic coincides with a strengthened sub-tropical anticyclone, and later to changes in low level winds that bring orographic convection to SE Ethiopia. The slower El Nino–Southern Oscillation (ENSO) interacts with the faster Indian Ocean Dipole (IOD), but both signals mature too late for direct use in statistical prediction of Sep–Nov rainfall. Composite differences of the upper divergent circulation exhibit a global wave-2 pattern consistent with satellite-observed convection. One key feature is a zonal gradient in upper velocity potential over the Indian Ocean corresponding with a zonal atmospheric circulation. One outcome of this research is useful forecasts of SE Ethiopia Sep–Nov rainfall that will assist in agricultural planning.

This study analyzes a convective outbreak over the Red Sea on 25 August 2009 that generated easterly waves over the Sahel, floods in Ouagadougou, and a hurricane in the east Atlantic. The convective outbreak occurred on the equatorward flank of the African easterly jet 18°–22°N and associated meridional heating gradients over the Arabian Peninsula. The Rift Valley mountains induced a vertical orographic undulation and cyclonic perturbation. Two thunderstorm clusters over the southern Red Sea received moist inflow from the Ethiopian highlands and northern Red Sea. This group of three easterly waves intensified downstream over the Sahel. One of the convective triggers was enhancement of the Arabian Ridge by the northern subtropical jet. Statistical analyses indicate that African easterly waves and subsequent tropical storms are more influenced by upstream kinematic shear than thermodynamic energy. The work offers new insights on the formation of easterly waves over the northern Rift Valley.

This study explores the structure and modulation of the mean diurnal climate of Africa with a focus on satellite rainfall. Solar heating over tropical mountains and land-sea temperature gradients initiate moisture convergence in the afternoon-evening. The diurnal temperature range is from 5 °C along the coast to 20 °C in arid zones with low vegetation fraction. NCEP2 reanalysis reveals the diurnal circulation via continental-scale drainage and seabreeze flows. Factors modulating the diurnal cycle vary across four sub-regions: South Africa, East Congo, Ethiopia, and Guinea. In the Congo and Guinea coast the surface moisture and heat fluxes are important, while in South Africa convective available potential energy and vertical motion are influential. Ethiopia’s evening orographic convection is out of phase with surface fluxes. The diurnal residual calculated from NCEP2 fields exhibits a 2 km depth for thermal gradients and 200 km inland penetration of onshore flow by evening.

Inter-relationships between physical ocean-atmosphere processes over the eastern Agulhas Bank are explored using data assimilation by the Hybrid Coordinate Ocean Model (HYCOM), which provides daily fields and time series off the south coast of South Africa (33.75–34.5S, 24.0–26.5E) in the period 2009–2017. Our objectives are: i) to describe and understand the sharp gradients over the shelf, ii) to quantify the temporal controls and lagged uptake of weather events and, iii) to analyze the spatial effects of capes on mesoscale oceanographic structure. Sea surface temperature (SST) and zonal winds (U-wind) were cross-correlated with salinity, currents, waves and atmospheric variables such as heat budget components, air pressure (SLP), air temperature. Correlations were made over daily and annual time scales to identify the leading ocean-atmosphere interactions and the strength of processes. At daily time scales weak correlations were found between SST and a variety of ocean-atmosphere parameters, suggesting that multiple processes affect the thermodynamic condition. SST showed most correlation with radiation and heat budget components (r = −0.35, 0.39), SLP (r = −0.30) and meridional currents (r = −0.26). In contrast, the simultaneous correlation of SST with U-wind was weak (r = −0.08). We attribute this to: i) delayed response, ii) opposing effects of coastal upwelling and summer heating, and iii) competing shelf-edge processes. Over the mean annual cycle, correlations between SST, U-winds, salinity, radiative fluxes and V-currents were strong, indicating how kinematic and thermodynamic controls conspire to induce seasonality. SST was well correlated (r Case studies of transient cold and warm events south of South Africa are described to reveal the large-scale atmospheric forcing of local SST. In addition, comparisons between the HYCOM reanalysis time series and independent insitu data are provided as a measure of confidence in global data assimilation systems, which open new opportunities for mesoscale oceanographic research in coastal zones.

Rain-fed agriculture in North-West (NW) Ethiopia is seasonally modulated, and our objective is to isolate past and future trends that influence crop growth. Statistical methods are applied to gauge-interpolated, reanalysis, and satellite data to evaluate changes in the annual cycle and long-term trends. The June to September wet season has lengthened due to the earlier arrival and later departure of rains. Meteorological composites relate this spreading to local southerly winds and a dry-south/wet-north humidity dipole. At the regional scale, an axis of convection over the Rift Valley (35E) is formed by westerly waves on 15S and an anticyclone over Asia 30N. Coupled Model Intercomparsion Project (CMIP5) Hadley2 data assimilated by the Inter-Sectoral Impact Model Intercomparision Project (ISIMIP) hydrological models are used to evaluate projected soil moisture and potential evaporation over the 21st century. May and October soil moisture is predicted to increase in the future, but trends are weak. In contrast, the potential evaporation is rising and may put stress on the land and water resources. A lengthening of the growing season could benefit crop yields across the NW Ethiopian highlands.

Observed and simulated climate trends across South Africa in the period 1980–2014 are studied. Observed CRU3/CAMS (Climate Research Unit v3 / Climate Analysis and Monitoring System) air temperatures have increased by 0.02°C·yr −1 while NOAA/SODA sea temperatures have risen by 0.03°C·yr −1 in the Agulhas Current. A poleward expansion of the South Atlantic high in NCEP2/MERRA (National Center for Environmental Prediction v2 / Modern-Era Retrospective analysis for Research and Applications) has produced a trend toward south-easterly flow which contributes to a moist-east/dry-west pattern. Observed CHIRPS2 rainfall and NDVI vegetation fraction show no appreciable trend except near Cape Town where drier conditions in the period 1980–2014 correspond with enhanced coastal upwelling. CMIP5 model projections for rainfall up to 2050 reflect drying, except in the eastern coastal plains. While inter-annual fluctuations of South African rainfall overshadow linear trends, temperature increases account for 32% of observed variance. Keywords : South Africa, climate change, satellite era

This study reconsiders the role of the Agulhas Current in South African climate variability. Here, the Agulhas Current is delimited by its anticyclonic looping flow and cluster analysis of detrended SST anomalies that lead to an area 28°–37°S, 18°–35°E, poleward of South Africa. Regression of detrended Agulhas SST with rainfall anomaly fields in the years 1950–2012 yields a surprising negative influence over the interior. In summer, the negative regression exhibits a northwest axis consistent with reduced cloud band activity. Positive influence is confined to the eastern escarpment in the September–November season when cutoff lows are prevalent. The overall negative influence of the Agulhas SST is confirmed by regression with the vegetation fraction and latent heat flux in the satellite era. Mechanisms of South African rainfall suppression were investigated. The Agulhas SST index is positively related to the multivariate ENSO index at the 1–3-month lead time. Hence, warm years in the Agulhas Current follow Pacific El Niño. Composite ocean analysis shows enhanced westerly winds offshore and a westward extension of warm salty water from the anticyclonic south Indian Ocean gyre. Composite atmospheric analysis exhibits moist uplifted air over the Agulhas Current folding into an equatorward circulation that sinks over the interior plateau. Because Agulhas SST partially follows ENSO, its suppression of interior rainfall is concluded to be passive.

Summer rainfall over the cropping region of Ethiopia is related to the precursor winter circulation around the Maritime Continent and El Nino–Southern Oscillation (ENSO) development and influence. Investigation of this link reveals that sea surface temperature (SST) in the north Indian Ocean and China Sea are anomalously cold and there are low level north-westerly wind anomalies around the Maritime Continent prior to dry summers in Ethiopia. The analysis shows that wind anomalies spread into the Pacific - increasing convection, and across the Indian Ocean and Africa - suppressing convection. Two indices that represent Asian winter monsoon penetration near the Maritime Continent are used to predict Ethiopian summer rainfall at long-lead time. The hindcast fit of the statistical algorithm exceeds 50% during the satellite era (1981-2014). Key words: Climate prediction, Ethiopia.

This study analyzes the climate of Madagascar (12°–26°S, 43°–50°E) and its relation to the Indian Ocean during austral summer (Dec–Mar). Moisture converges onto a standing easterly wave and floods are prevalent in late summer. All-island daytime land temperatures exceed 38 °C in October and are ~4 °C above sea temperatures during summer. Analysis of thermally induced diurnal convection and circulation revealed inflow during the afternoon recirculated from the southeastern mountains and the warm Mozambique Channel. Summer rainfall follows latent and sensible heat flux during the first half of the day, and gains a surplus by evening via thunderstorms over the western plains. At the inter-annual time-scale, 2.3 years oscillations in all-island rainfall appear linked with the stratospheric quasi-biennial oscillation and corresponding 80 Dobson Unit ozone fluctuations during flood events. Wet spells at frequencies from 11–27 days derive from locally-formed tropical cyclones and NW-cloud bands. Flood case studies exhibit moisture recycling in the confluence zone between the sub-tropical anticyclone and the lee-side vortex. Hovmoller analysis of daily rainfall reinforces the concept of local generation and pulsing by cross-equatorial (Indian winter) monsoon flow rather than zonal atmospheric waves. Since the surface water budget is critical to agriculture in Madagascar, this study represents a further step to understand its meso-scale summer climate.

Climate variability in the eastern Antilles island chain is analyzed via principal component analysis of high-resolution monthly rainfall in the period 1981–2013. The second mode reflecting higher rainfall in July–October season between Martinique and Grenada is the focus of this study. Higher rainfall corresponds with a weakened trade wind and boundary current along the southern edge of the Caribbean. This quells the coastal upwelling off Venezuela and builds the freshwater plume east of Trinidad. There is corresponding upper easterly wind flow that intensifies passing tropical waves. During a storm event over the Antilles on 4–5 October 2010, there was inflow from east of Guyana where low salinity and high sea temperatures enable surplus latent heat fluxes. A N–S convective rain band forms ∼500 km east of the cyclonic vortex. Many features at the weather timescale reflect the seasonal correlation and composite difference maps and El Nino Southern Oscillation (ENSO) modulation of oceanic inter-basin transfers.

This study considers tropical cyclones Irene in Puerto Rico from 2011 and Isaac in the Dominican Republic from 2012. Impacts trailed more than a day after the storm in both cases. Irene passed Puerto Rico on 22 August 2011, yet bands of heavy rainfall caused floods and disruption on 23 August. In the second case, Isaac passed Hispaniola on 24 August 2012, but stormy weather continued on 25 August. Onshore winds, 4-m waves, and associated tides and river outflow closed the harbor of Santo Domingo. Emergency managers and maritime operators should be aware of the delayed impacts of tropical cyclones in the Caribbean Sea region.

Interannual variability of tropical cyclones (TCs) in the eastern Caribbean is studied using MIT-Hurdat fields during the July–October season from 1979 to 2008. TC intensity shows local climate sensitivity particularly for upper ocean currents, salinity and mixed-layer depth, and 200–850 mb wind shear. Remote influences from the Southern Oscillation, Saharan dust, and the South American monsoon are also identified as important. Ocean currents diminish along the coast of South America, so interbasin transfer between the North Brazil and Caribbean Currents declines in seasons of frequent and intense TCs. This is related to a dipole pattern in the sea surface height formed mainly by reduced trade wind upwelling northeast of Venezuela. A low-salinity plume from the Orinoco River spreads across the eastern Caribbean. It is the weaker currents and shallower mixed layer that conspire with surplus heat to build thermodynamic energy available for TC intensification.

To investigate topographic–thermal circulations and the associated moisture variability over western Puerto Rico, field data were collected from 15 to 31 March 2011. Surface meteorological instruments and ground-based GPS receivers measured the circulation and precipitable water with high spatial and temporal resolution, and the Weather Research and Forecasting (WRF) Model was used to simulate the mesoscale flow at 1-km resolution. A westerly onshore flow of ~4 m s−1 over Mayaguez Bay was observed on many days, due to an interaction between thermally driven [3°C (10 km)−1] sea-breeze circulation and an island wake comprised of twin gyres. The thermally driven sea breeze occurred only when easterly synoptic winds favorably oriented the gyres with respect to the coast. Moisture associated with onshore flow was characterized by GPS measured precipitable water (PW). There is diurnal cycling of PW > 3 cm over the west coast during periods of onshore flow. The WRF Model tends to overestimate PW on the west side of the island, suggesting evapotranspiration as a process needing further attention. Fluctuations of PW affect local rainfall in times of convective instability.

The meteorological influences on Caribbean air chemistry are studied using in-situ, satellite and model data. Although African dust plumes join locally generated pollutants, concentrations are relatively low in the eastern Caribbean due to geographic remoteness and steady oceanic trade winds. Urban-industrial emissions from big cities (e.g., Kingston, Santo Domingo, San Juan), agricultural emissions from the south, and volcanic emissions from Montserrat contribute a noticeable burden. Conditions over Puerto Rico in the dry season (December–May) provide a focus for statistical analysis of air chemistry constituents and weather variables that describe dispersion conditions. Monthly and daily air indices are formed by summing the normalized values of fine aerosols and particulates, long- and short-lived trace gases from in-situ, satellite and model sources. The spatial correlation of a daily Puerto Rico air index onto regional dewpoint temperature, air pressure and outgoing longwave radiation fields in December–May 2005–2015 reveals the northward movement of a dry tongue and trough. At the climate timescale, Pacific El Nino conditions favor an increase of spring-time air pollution corresponding to anomalous inflow from Africa and the southern Caribbean coast. Composite weather patterns for a group of high air index values reflect divergent trade winds and a strong jet stream that imparts anticyclonic vorticity, subsidence and low humidity. This new understanding will underpin better air quality forecasts for Puerto Rico and the wider Caribbean.

This study considers eastern Antilles (11°–18°N, 64°–57°W) weather and climate interactions in the context of the 2013 Christmas storm. This unseasonal event caused flash flooding in Grenada, St. Vincent, St. Lucia, Martinique, and Dominica from 24 to 25 December 2013, despite having winds

This study describes hydrological fluctuations of Lake Abaya-Chamo via direct local measurements in relation to time-integrated climate anomalies. Reconstruction of an index involved compositing lake level and flow discharge station records in the period 1983-2009. Satellite and model interpolated rainfall, latent heat flux and run-off anomalies follow the hydrological records when summed over and lagged by one year. Correlation of ECMWF climate fields reveals that east Pacific and subtropical Atlantic surface temperature are influential on continuous flow discharge, while the Indian Ocean dipole has influence in September to November season. A predictive algorithm accounts for 44% of inter-annual fluctuations in the period 1983-2009. Rapid increases in lake level coincide with maturing El Nino and Indian Ocean dipole, bringing floods for example in October 1997. Early season dry spells prevail when the equatorial trough remains over Tanzania, and dry northerly winds accelerate evaporation such as in March 2000. Key words: Ethiopia rift lakes, hydrological fluctuations.

Hydrological fluctuations of Malawi’s Shire River and climatic drivers are studied for a range of time and space scales. The annual cycles of basin rainfall and river flow peak in summer and autumn, respectively. Satellite and model products at

The Southern Benguela cape upwelling plumes have inshore wind shadows prone to red tides in late summer. Their intensity and coverage are estimated by satellite fluorescence measurements in the period 1997–2012 and qualified by in situ reports. High satellite fluorescence cases are identified at daily to seasonal time scales, and characteristics of the upper ocean and lower atmosphere are studied using third generation reanalyses. A dominant feature is easterly winds over the Cape Peninsula (34°S, 18°E) induced by a ridging anticyclone-coastal low weather pattern. Over Cape Columbine (33°S), there is a wind shadow with cyclonic wind and current shear. Composite atmospheric profiles reveal a 4°C temperature inversion near 500 m that traps a coastal wind jet >6 m/s below 200 m. The composite shelf oceanography shows a relic upwelling plume below 10 m overtopped by warmer water near the coast, providing the thermal stratification needed for biotic aggregation. Data from the IPSL5 coupled climate model over the period 1980–2080 indicates that environmental conditions favoring red tides may become more frequent.

South African rainfall in the period 1960–2010 exhibits ∼12-year oscillations of similar amplitude to those at 2–5 years. Corresponding global climate signals, as deduced from principal component analysis, include ocean heat content (HC2) and upper zonal winds (2U1) primarily in the Pacific sector. Composites of wet and dry summers are analyzed as depth and height sections to understand the ocean–atmosphere coupling that generates low frequency oscillations. Point-to-field correlations with respect to decadal-filtered South African rainfall (SA1) reveal how the Pacific signals connect with Africa through upper zonal winds, vorticity cells, sea temperature, and aerosol concentration. A regression algorithm of HC2 and 2U1 explains 58 % of the decadal SA1 variance and peak years 1976 and 2000. Although the HC2 pattern is asymmetric and independent, 2U1 principal component time scores follow the Multivariate El Nino Southern Oscillation Index and Pacific Decadal Oscillation. The conveyor of tropical easterlies that dips over the SW Indian Ocean subsequently rises over southern Africa bringing rain with a decadal frequency.

This study compares Climate Research Unit version 3 reference observations in the period 1980–2009 with Coupled Model Intercomparison Project Five (CMIP5)-simulated climate patterns and trends over the Ethiopian highlands (7–14N, 36–40E) using the rcp6 scenario. Three metrics are used in a stepwise statistical evaluation: (1) mean annual cycle of area-averaged rainfall (R) and maximum temperature (Tx), (2) spatial pattern of R and Tx over Ethiopia and (3) interannual (1.5–6 years) R and Tx variability. Those models passing the first step by simulating a unimodal annual cycle reaching 28 °C in March–May and 9 mm day−1 in July–August are then evaluated for their ability to represent the cool, wet ‘island’ pattern over the highest elevation. Finally, the models' ability to follow observed area-averaged R and Tx anomalies from 1980 to 2009 is analysed by correlation. The stepwise metrics are designed to improve confidence in the use of CMIP5 models for future resource management and development planning across the Ethiopian highlands. The models with optimal performance in the most categories include the HAD, CCSM and GFDL.

One of the weather-related shipping hazards in the Caribbean Islands is an intense anticyclone during winter. Surges of trade winds cause steeply sloped short-period ( 2 m) waves to penetrate the shipping lanes near Puerto Rico. In addition to the large-scale air pressure gradient (5 hPa/300 km), the Antilles Islands funnel the winds (>10 m/s) and accentuate the surface heat fluxes (>200 W/m2) and air-sea momentum transfer. Here, the weather scenario surrounding a case of damage to a supply ship 30–31 December 2015 is presented, when the wave height-to-length ratio exceeded 3%. This case is placed in context by statistical analysis of climate and weather features contributing to intensified trade winds. A negative Pacific-North America pattern during La Nina enhances an anticyclonic ridge north of Puerto Rico, contributing to steep waves. The research highlights the hazard to shipping of short-period waves produced by surges of trade winds.

Meteorological controls on big waves south of Africa in the period 1987–2013 are described. European Community daily climatology since 1987 shows that waves from the SSW off East London at 34S, 27.5E are most frequent in the range 2–4 m and 8–10 s, and pass through a warm pool where heat fluxes amplify air–sea momentum transfer. Time series of 3-hourly Wavewatch v3 swell direction, height and period data at a key point near East London since 1998 provide a basis for analysis, and reveals numerous cases of big SSW wave events during the winter months from May to September. A composite of the six largest cases was made by averaging meteorological fields over a large area south of Africa. The big-wave composite reveals a 975 hPa deep low at 51S, 33E that is slowed by a blocking high in polar latitudes. The highest ranked winter storm case within the time series forms a case study: 24–26 June 2009, and reveals a cold air outbreak producing heat fluxes up to 800 W/m2 under 20 m/s southerly winds in a massive fetch area 35–60S, 15–30E. Swells of 8 m reached the South African coast, damaging infrastructure there.

This study evaluates seasonal forecasts of rainfall and maximum temperature across the Ethiopian highlands from coupled ensemble models in the period 1981–2006, by comparison with gridded observational products (NMA + GPCC/CRU3). Early season forecasts from the coupled forecast system (CFS) are steadier than European community medium range forecast (ECMWF). CFS and ECMWF April forecasts of June–August (JJA) rainfall achieve significant fit (r2=0.27, 0.25, resp.), but ECMWF forecasts tend to have a narrow range with drought underpredicted. Early season forecasts of JJA maximum temperature are weak in both models; hence ability to predict water resource gains may be better than losses. One aim of seasonal climate forecasting is to ensure that crop yields keep pace with Ethiopia’s growing population. Farmers using prediction technology are better informed to avoid risk in dry years and generate surplus in wet years.

The Turks and Caicos Islands (TCI) climate is described using mesoscale ocean and atmosphere datasets with a focus on thermodynamic versus kinematic controls, the influence of the nearby island of Hispaniola, and factors affecting early colonization and fluctuations of marine resources. The key findings include the following: trade winds accelerate to 7 m s−1 north of Hispaniola and enhance anticyclonic subsidence; there is a dry-south/wet-north pattern of rainfall that opposes surface temperature and salinity fields; ocean currents near TCI are northwestward but there is a counterclockwise gyre near Haiti that guided colonization; conch catch increases when trade winds strengthen and SST declines; TCI's dry climate limits groundwater resources, food production, and population density; and Caicos Island sheds a wind wake that boosts SST and local convection, as evident in Quick Scatterometer (QuikSCAT) observations and operational model products. Further studies of small island climates will benefit from an ever-increasing stream of mesoscale datasets.

This study compares different methods of predicting crop-related climate in the Ethiopian highlands for the period 1979–2009. A target index (ETH4) is developed as an average of four variables in the June–September season—rainfall, rainfall minus evaporation, estimated latent heat flux, and vegetation, following correlation with crop yields at Melkassa, Ethiopia (8.4°N, 39.3°E, 1550 m elevation). Predictors are drawn from gridded near-global fields of surface temperature, surface air pressure, and 200-hPa zonal wind in the preceding December–March season. Prediction algorithms are formulated by stepwise multivariate regression. The first set of predictors derive from objective principal component (PC) time scores with tropical loading patterns, and the second set is based on key areas determined from correlation with the target index. The second PC of upper zonal wind reveals a tropical–subtropical dipole that is correlated with ETH4 at two-season lead time (correlation coefficient r = −0.53). Point-to-field regression maps show high-latitude signals in surface temperature (positive in North America and negative in Eurasia) and air pressure (negative in the North Pacific Ocean and positive in the South Pacific). Upper zonal winds are most strongly related with ETH4 over the tropical Pacific and Africa at two-season lead time. The multivariate algorithm that is based on PC predictors has an adjusted r2 fit of 0.23, and the algorithm using key-area predictors achieves r2 = 0.37. In comparison, numerical model forecasts reach r2 = 0.33 for ECMWF simulations but are low for other models. The statistical results are specific to the ETH4 index, which is a climate proxy for crop yields in the Ethiopian highlands.

This paper reviews long-range climate prediction with a focus on experiences in southern Africa from 1990 to 2005 and statistical techniques based on historical replication. The initial growth and use of climate predictions in southern Africa created an understanding of tropical Atlantic and Indian Ocean coupling with Pacific El Nino and the African monsoon, and fostered extensions of the global observing system as a key outcome. An intercomparison of forecast errors highlights optimal scales for model aggregation. Cases of forecast development are analyzed and a tendency for neutral messages is found. South African maize yield exhibits an uptrend (+0.26 T ha−1/year) since 1992 that may be related to the increased use of Internet and uptake of long-range forecasts.

Climate change in Hispanola is studied since 1900 using a variety of datasets. The longer station-observed temperature record has a significant trend of 0.012 °C/year, while the shorter reanalysis datasets exhibit faster warming, suggesting accelerating greenhouse radiative absorption and Hadley circulation. Rainfall trends are insignificant in the observed period, but a CMIP5 model simulation predicts a significant drying trend. The spatial pattern of climate trends was mapped with reanalysis fields and indicates a faster rate of warming over the eastern half of the island, where observations are dense and the drying trend is greatest. Northeasterly trade winds strengthen on the Atlantic side of the island. While trends intensify in the satellite era compared to the earlier 20th century, part of that effect is ascribed to an upturn in the Atlantic Multi-decadal Oscillation.