• What can we usually expect during this period?
  • Climatically, June to August forms the summer part of the Caribbean Heat season, the first half of the wet season in Belize and the Caribbean Islands, as well as the first half of the Atlantic Hurricane Season. All of these should reach their annual peak by the end of August.
  • This period is characterised by higher night- and daytime temperatures, increasing air humidity and tropical cyclone activity, a significant increase in the frequency of heatwaves, wet days and wet spells, but a decrease in the number of dry days and dry spells compared to the previous three months (March to May). However, in portions of the Greater Antilles, a drier period of about 3-6 weeks tends to break up the wet season into two parts.
  • As the ground surface and foliage becomes more moisture-laden, wildfire potential, the concentration of airborne particulates and local dust levels should decrease during June.
  • In the Guianas, the primary wet season tends to end in early-August. Until then, the frequency of heavy rain showers should remain steady. As the primary dry season sets in later in August, temperatures should increase, and the first heatwaves may occur as rainfall and moisture levels decrease.
  • The frequency of Saharan dust incursions into the Caribbean tends to peak until July and slowly decrease from August onwards. Access more detailed forecast information on dust and air quality in the Caribbean 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 11-12 (extremely high) throughout the period.
• What is different this year?
  • Ocean temperatures in the tropical Pacific have increased to well-above average in recent weeks, making it exceedingly likely that the Pacific will transition into El Niño. At the same time, North Atlantic ocean temperatures in and around the Caribbean are expected to be and remain well above-average.
  • Unusually warm waters in these two ocean basins will steadily amplify heat stress by increasing temperatures, humidity and heat wave frequency. As such, there is very high confidence that the 2023 Heat Season will be a very hot one. In fact, it may end up similar to the record-breaking 2020 Heat Season in terms of heat stress.
  • Therefore, while prioritising preparedness for hurricanes and other severe weather events, this year an additional priority for climate risk management should be heat and associated impacts.
  • However, this unusual combination of a warmer tropical Pacific and Atlantic will provide counteracting forces in terms of rainfall totals and extremes, as well as in terms of tropical cyclone activity^[1]. Hence, until we can physically observe whether the influence of the El Niño or the warmer than usual waters around the Caribbean will dominate, we have low confidence in forecasting rainfall deficits (i.e., drought) or changes in frequency and intensity of severe weather-related hazards.
• In light of the very warm tropical Pacific and North Atlantic, the forecast for June to August 2023 suggests:
  • The 2023 Atlantic Hurricane Season officially started on June 1st and is forecast to be as active as usual with an estimated 13-17 named storms (i.e. tropical storm, hurricane or major hurricane) (high confidence), including approximately 6-8 hurricanes (medium confidence), of which 3 or 4 may easily intensify into a major hurricane (i.e., category 3, 4 or 5 on the Saffir-Simpson scale) (medium confidence) over the entire season. As of June 5th, one sub-tropical storm occurred in January and one on June 2nd.
  • Seasonal night-time and day-time temperatures in the Caribbean are expected to be even warmer than usual and accompanied by high levels of air humidity (high confidence).
  • Frequent heat waves are expected, especially towards August. At least 15 – and possibly up to 30 or more – heatwave days are expected over this three-month period throughout the Caribbean Islands (high confidence). 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.
  • 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/.
  • The usual or even higher seasonal rainfall totals are expected across most of the Greater Antilles and the Leeward Islands. By contrast, the ABC Islands, The Bahamas, Barbados, Cayman Islands, eastern parts of 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 excessive rainfall will be high (i.e., occurs at least once every other year) to extremely high (i.e., occurs at least four years out of five) in Belize; high in The Bahamas, Barbados, most areas in the Greater Antilles, Guyana, the USVI, and the Windward Islands; and moderate (i.e., occurs at least once every 5 years) in the ABC Islands and the Leeward Islands. 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 (on a 6 months timescale) may possibly develop in southern French Guiana by the end of August 2023 (medium confidence).  Short  term  drought  may  impact food  production,  water  quality  and  quantity  from  small  streams,  small  ponds  and  other surface  Long term drought (on a 12 months timescale) may possibly develop in Dominica and Trinidad by the end of November 2023 (medium confidence). Long term drought 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.
• ^[1] On the one hand, El Niño in the Pacific increases chances of rainfall deficits, dry spells and drought, but tends to weaken tropical cyclone activity. In stark contrast, a warmer than usual tropical North Atlantic increases chances of high rainfall totals, frequent wet days, wet spells and heavy showers, as well as tropical cyclone activity.

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.