• What can we usually expect during this period?
  • Climatically, March to May forms the late Dry Season in Belize and the Caribbean Islands.
  • This season is characterised by relatively few wet days and a small number of wet spells, but many dry days and a few dry spells.
  • The resulting drier surface and foliage increase wildfire potential and the concentration of airborne particulates. Local dust levels should also be increasing during prolonged dry spells and towards the end of the dry season.
  • In the Guianas, the Greater Antilles and, in many years, the Leeward Islands, the wet season tends to start in May, with a return of heavy rainfall.
  • Coincidentally, largely fueled by drier soils, the Caribbean Heat Season – characterised by the recurrence of heatwaves – commences in April (in Belize, Cuba, Trinidad) or May (elsewhere except for the Guianas).
  • In addition, though the 2024 Hurricane Season officially starts on 1 June, tropical cyclones have occurred and are increasingly common before that date.
  • The frequency of Saharan dust incursions into the Caribbean tends to increase during this period to peak starting in May. It should be noted that, in some years, significant Saharan dust episodes also occur in March and April. (Access more detailed forecast information on dust and air quality in the Caribbean may be found here: http://dafc.cimh.edu.bb/).
  • UV exposure is set to be dangerously elevated. On a scale from 1 to 12, the UV index on sunny days will be 8-10 (very high) to 11-12 (extremely high).

• What is different this year?
  • This year, a waning El Niño event will likely make way for its cold counterpart in the tropical Pacific Ocean, namely a La Niña, by June-July-August.
  • In the North Atlantic Ocean and the Caribbean Sea, (near-) record high sea surface temperatures are expected to prevail.
  • Years in which El Niño wanes and Atlantic Ocean temperatures are high typically drive (1) a strong uptick in excessive, humid heat in the Caribbean to the point of significant heat stress in the Heat Season; (2) an early and often abrupt transition into the wet season – particularly in Barbados, Trinidad and Tobago and the Windward Islands –; and (3) an early onset of an active Atlantic Hurricane Season.
  • A reasonable past example similar to this year’s observed and forecasted conditions is the year 2010, when
    • The worst region-wide drought in decades was abruptly interrupted by an earlier return to the wet season in April and May. Despite the drought early on, 2010 ended up being the wettest year on record in many places and triggering extensive episodes of flooding, flash floods and cascading impacts (e.g., landslides), as well as damage and losses resulting from such.
    • A very active hurricane season (2010 was the most active season since 2005), associated with >300 direct and >75 indirect casualties.
    • Region-wide, record-breaking air and Caribbean Sea temperatures, as well as the earliest onset on record of the heat season and associated occurrence of heatwaves, exacerbating drought and wildfire weather until April.
  • While 2010 may be the best past example to paint a picture of the 2024 scenario, the timing of the start and the intensity of the wet, heat and hurricane seasons will ultimately further depend on the frequency of atmospheric patterns that are conducive to or suppress ‘deep convection’ – i.e., strong vertical updraughts of hot and mostly humid air, driving severe weather.
    One well-known example of suppressive conditions is the frequency of intrusion of very dry (and, at times, dust-laden) air from the Sahara higher up in the atmosphere, the so-called ‘Saharan Air Layer’ or SAL.
  • If SAL intrusions end up more frequent than usual, 2024 will be even hotter – potentially breaking 2023’s record heat season – & more humid, often with hazy conditions at the surface. By contrast, more Saharan air intrusions fortunately also translate to reduced tropical cyclone activity and fewer wet days and wet spells, reduced potential for flooding, flash floods and associated hazards and impacts. Conversely, any ongoing drought concerns may be prolonged, with increased wildfire potential and frequency of dry spells.

• The March-April-May 2024 outlook in further detail:
  • Seasonal rainfall amounts are forecast to be the usual or even less in The Bahamas, Cayman Islands and Cuba, but the usual or higher in the ABC Islands, Hispaniola, the US Caribbean Territories, the Lesser Antilles and the Guianas (medium confidence).
  • Short-term drought is expected to be a significant concern by the end of May 2024 in southern French Guiana (medium to high confidence), but also possible in southern Belize, Grand Cayman, central French Guiana, northeastern Guyana, Jamaica, and the USVI (medium confidence). Short-term drought may impact food production, water quality and quantity from small streams, small ponds and other surface sources.
  • Long-term drought is evolving by the end of May 2024 in southwest Belize, Grand Cayman, inland portions of French Guiana, northeastern and inland portions of Guyana, southwest Puerto Rico, northern Suriname (high confidence) and might possibly develop or continue in the northern Belize, Central Cuba, Dominica, coastal French Guiana, northern Guyana, Tobago, the USVI (medium confidence). Long-term drought (on a 12-months 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.
  • Severe weather systems related to tropical cyclones, as well as heavy showers may affect Caribbean territories repeatedly in April and May. 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/).
  • Night-time and daytime temperatures are forecast to be higher than usual in most areas (high confidence). Significant episodes of heat stress may, therefore, appear as the region is forecast to transition into the Heat Season in April. However, heatwaves might already be recorded this March, notably where soil moisture content is even lower than usual.

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.