CASTRIES, St Lucia (CMC) — The Caribbean faces “a lot of variables” as the region transitions from the wet hurricane season into the dry season, which runs from December to May, regional forecasters said on Thursday.
Saharan dust intrusion might influence how the dry season turns out, Vigil Saltibus, acting director of the St Lucia Meteorological Services, told the 2024-25 Dry Season Caribbean Climate Outlook Forum (CariCOF) here.
Saltibus presented the outlook during the event held twice annually by the Barbados-based Caribbean Institute for Meteorology and Hydrology (CIMH).
She said one possible scenario is the usual frequency of the Saharan Air Layer intrusion, noting that while the dry season runs from December to May, December is a transition month.
Saltibus said that with the Saharan air layer frequency, the dry season would begin with intense dryness in the northwestern Caribbean and a delayed start to the season in the southeast of the region.
“It means accelerated depletion of surface water reservoirs and reduced river discharge, increase in wildfire potential towards March, particularly in areas affected by drought,” Saltibus explained.
She noted that March is the peach of the dry season in the Eastern Caribbean, adding that indications are that there’s a possibility of the region being unusually dry by this time, even with the usual levels of Saharan dust intrusion.
The other scenario is for very frequent Saharan air layer intrusions during the dry season.
“It means that more dry spells and worsening drought towards May may occur, slower drought alleviation after May, and a slight decrease in wildfire potential. The slower drought alleviation after May is not a good indication,” Saltibus said.
“That means towards the end of our dry season, where we should be starting off our wet season, there may be a possibility of a delayed wet season.”
Regarding how dry the Caribbean would be during the dry season, Saltibus said that the drought is not expected to be a concern in the Lesser Antilles.
“But there are some islands, including St Lucia and Dominica, where drought is possible,” she said, adding that the situation is evolving.
“So we have to continue to monitor each month, our rainfall, in the coming months, during our dry season to see how this pans out,” Saltibus said, reminding the conference that “this is a model”.
“A model is guidance. Don’t take it as gospel. You have to continue to monitor and observe.”
In the short term, through February 2025, models suggest a probability there may be at least three seven-day dry spells.
“The seven-day dry spells is three consecutive days with rainfall being at least less than one millimetre of rainfall.”
However, looking at the long-term drought period through the end of May — the end of the dry season — there are pockets of drought warnings and drought watches over the British Virgin Islands and parts of Puerto Rico.
“… but for most of us, there is no concern for drought, hopefully; fingers crossed, but we’ve just mentioned Saharan early intrusion. There are two possible scenarios,” Saltibus said, noting that the dry season can be drier than usual or the wet season wetter than usual.
She said frequent and intense rains through December could result in a high potential for flooding, flash floods, cascading hazards and impacts.
“And you have frequent rains in the southeast that are conducive to moisture-related pests. Looking at this alternative scenario, the very frequent Saharan Air Layer intrusion, you could have erratic, intense wet spells from May to July.
“So forecast said, sub-seasonal differences in rainfall. We’re looking at the start of the dry season, which is December to February, it may be wetter than usual for the early dry season in areas southwards of Guadeloupe, but the usual or even drier elsewhere.”
Forecasters have also addressed the question of heat in the dry season, noting that the Saharan dust intrusion would play a major role in this regard.
“Our influencer here is a Saharan air layer. We’re going for a cool season between December and February, followed by an early start of an intense heat season,” Saltibus said.
“It means warmer nights and days than usual, yet more comfortable during the cool season. We have frequent and intense heat waves from May, and intense marine heat waves through December continue to trigger coral bleaching and heat stress in marine ecosystems decreasing through April.”
She said the alternate scenario shows humid heat approaching 2023 and 2024 levels from May.
“So we’re comparing last year and this year, and you could see that the humid heat approaching is going to be very high because we had a record 2023, we had a record 2024 and if we anticipate in 2025 as it’s looking to be another hot 2025.”
The forecast is for a cool season from the first half — from December to February — “it comes with mostly comfortable temperatures, though still warmer than usual for the season in most areas”.
“The latter half of the dry season, April and May, the transition into 2024, the heating season, to feature a rapid warming, except if very wet,” Saltibus said.
She said the implications are for a low chance of heat stress episodes in the vulnerable population and small livestock until February, but becoming increasingly frequent and intense in April and May.
“Heat waves are increasingly likely in April and in May,” Saltibus added.