• What we usually expect during this period
  • Climatically, September to November forms the second half of the wet season in the Caribbean islands and in Belize. During this period, a large number of wet days and frequent wet spells occur. However, a number of short dry spells still can punctuate this season, particularly in the Greater Antilles.
  • By contrast, the Guianas are in their hot, dry season, running into November in most areas, but continuing through April in far inland, southwestern parts of the region. Hence, frequent dry spells, but infrequent wet days and wet spells are the historical norm from September to November.
  • The 2023 Atlantic Hurricane Season officially lasts until November 30th, with the peak of tropical cyclone activity typically lasting until mid-October, but storms and hurricanes have occurred after the official end date.
  • September and October form the last two months of the Caribbean Heat Season. These months are characterised by higher night- and daytime temperatures, peaking air humidity and a high frequency of heatwaves through September in The Bahamas, Belize, the Greater Antilles and the Leeward Islands, through October in the ABC Islands, Barbados, the Guianas, Trinidad and Tobago and the Windward Islands.
  • In the Caribbean islands and Belize, the ground surface and soils become more moisture-laden, often to the point of saturation. When intense showers occur, the potential for flooding, flash floods and associated hazards such as land slippage, rock fall and soil erosion is particularly high. With a full foliage, potential wind damage related to tropical cyclones is increased. On the bright side, wildfire potential, the concentration of airborne particulates, the frequency of Saharan dust incursions and local dust levels should be low during this period. Access more detailed forecast information on dust and air quality in the Caribbean here: http://dafc.cimh.edu.bb/.
  • By contrast, with a peaking frequency of short dry days and short dry spells, the ground surface and soils in the Guianas usually lead to a reduction in flood potential, but an uptick in wildfire potential, the concentration of airborne particulates and local dust levels.
  • Across the region, swells, surges and rip currents from tropical cyclones – even if remotely located –, can be particularly hazardous to life and engender beach erosion. (Seven-day forecasts of swell heights may be found here: WaveWatch III (cimh.edu.bb)
  • Notwithstanding that it is the wettest part of the year in the Caribbean Islands and Belize, there remains a high risk of skin damage due to intense ultraviolet (UV) light emitted by the sun. The UV index will progressively decrease from extremely high (11-12) to very high (9-10) on sunny days towards November.
• What is different this year?
  • This year, El Niño conditions are in place in the tropical Pacific Ocean. El Niño more often than not is marked by a warmer heat season, a drier summer season, and reduced Atlantic Hurricane Season activity, especially from September to November.
  • In addition, near-record temperatures in the North Atlantic Ocean also contribute to higher air temperatures and a greater frequency of heatwaves in the Caribbean. However, this unusual heat in the North Atlantic Ocean also tends to increase humidity and seasonal rainfall totals, as well as the frequency of severe weather during the wet season.
  • Unusually warm waters in these two ocean basins will amplify heat stress by increasing temperatures, humidity and heat wave frequency. As such, there is very high confidence that the 2023 Heat Season will challenge the record-breaking years 2010, 2016 and 2020 in terms of heat stress.
  • Therefore, while preparing for hurricanes and other severe weather events remains a priority, this year an additional priority for climate risk management should be on heat and associated impacts, at least through October.
  • It appears that the warmer North Atlantic temperatures have thus far been dominant over the El Niño in driving hurricane season activity upwards, with an above-normal tally of 12 Tropical Storms, including 3 hurricanes of which 2 were major (category 4) hurricanes as of 31 August 2023.
• In light of the very warm tropical Pacific and North Atlantic, the forecast for September to November 2023 suggests:
  • The September to November second half of the Hurricane Season is still predicted to be close to or even more active than average, likely ending up with another 5-12 named storms, 3-8 hurricanes, and up to 3 major hurricanes (medium confidence). However, even higher numbers cannot be excluded.
  • Seasonal night-time and day-time temperatures in the Caribbean are expected to be even warmer than usual and accompanied by even higher than usual levels of air humidity (high confidence).
  • Frequent heat waves are expected, especially in September. At least 15 – and possibly up to 30 or more – heatwave days are expected over this three-month period in Barbados, the Guianas, Trinidad & Tobago and the Windward Islands, leading to high heat impact potential in these areas (high confidence).
  • More information on the expected heat and its implications on society and environment can be found in the latest Heat Outlook product issued by the CIMH at: https://rcc.cimh.edu.bb/heat-outlook/. Note: In the aftermath of a debilitating severe weather event, exposure to the combination of humid heat and recurrent heat waves can become severely dangerous to human life if unmitigated.
  • The usual or even higher seasonal rainfall totals are expected in the ABC Islands, and the Leeward Islands. By contrast, the Bahamas, Barbados, Belize, Cayman Islands, the Guianas, Trinidad & Tobago and the Windward Islands are likely to record the usual rainfall amounts or less (medium confidence).
  • Flash flood and long-term flooding potential arising from intense showers will be extremely high (i.e., occurs at least once in most years) in Belize, Cayman Islands, Cuba, Puerto Rico and USVI, but also high (i.e., occurs at least once every two years) to extremely high across the remainder of the Caribbean region. Persons should keenly monitor weather advisories issued by the National Meteorological Services and other information provided by the Caribbean Disaster Emergency Management Agency (http://cdema.org/) and the US National Hurricane Center (https://www.nhc.noaa.gov/).
  • However, even where less than the usual rainfall totals are recorded in the next few months, these will not raise major concerns for drought. Short-term drought is not expected to be a significant regional concern by the end of November 2023. Short-term drought may impact food production, water quality and quantity from small streams, small ponds and other surface sources. Long-term drought might possibly continue in St. Vincent or develop in St. Barts and Sint Maarten/St-Martin by the end of November 2023. Long-term drought (on a 12-month timescale) affects water availability across a multitude of socio-economic sectors in countries where the main freshwater resource is from very large rivers, large reservoirs or groundwater. Though major impacts are not expected, it should be noted that areas ending up in drought by the end of the wet season are prone to experiencing impacts during the ensuing dry season.

This Bulletin provides a broad overview of climate conditions up to 3 months in advance. It is based on insights drawn from CIMH’s suite of technical climate information products and epidemiological insights from CARPHA and PAHO. The information contained herein is provided with the understanding that the CARPHA, the PAHO and the CIMH make no warranties, either expressed or implied, concerning the accuracy, completeness, reliability or suitability of said information. The Bulletin may be freely used and disseminated by the public with appropriate acknowledgement of its source but shall not be modified in content and then presented as original material.