by Kevon Browne
St. Kitts and Nevis (WINN)—Climate change is reportedly causing asymmetry in the seasonality of the traditional dry and wet seasons in the Caribbean, resulting in longer, harsher dry seasons and shorter, more volatile wet seasons.
While the fundamental timing of the region’s meteorology remains anchored by global climate systems, the distinct boundaries between the seasons are blurring into a pattern of extended drought punctuated by extreme, concentrated rainfall.
Regional tracking by the Caribbean Institute for Meteorology and Hydrology (CIMH) and researchers at the University of the West Indies (UWI) shows a distinct structural contraction and extension.
The traditional dry window, which typically runs from December to May, is systematically encroaching on the wet season, according to experts, because higher baseline temperatures increase evaporation rates, causing dry conditions to set in earlier and last longer into the summer months.
Multiple climatic factors cause the extended dry season.
Meteorologist Denel Dixon of the St. Kitts Meteorological Services Office during a recent broadcast of the National Emergency Management Agency’s (NEMA) ‘From Danger to Safety’“Those two things can be, one the El Niño, and two climate variations. The El Niño: during El Niño years, we normally see less rainfall than in usual years, as it relates to the climate variability. In the past, we would have seen upper-level troughs coming through and affecting the island during the periods between February and May. This year we would not have seen any, and those normally bring a good bit of rainfall. So unfortunately we didn’t have any, so we don’t have the rainfall to show.”, Meteorologist Denel Dixon of the St. Kitts Meteorological Services Office during a recent broadcast of the National Emergency Management Agency’s (NEMA) ‘From Danger to Safety’.
“Despite the Pacific Ocean being very far away from us, the El Niño has global impacts, and for us it brings extra heat to the atmosphere and stronger upper-level winds. The stronger upper-level winds hamper storm development. Usually for storms to develop, they need their tops to grow as high as possible, but with the strong upper-level winds, it blows the tops off. The added heat in the atmosphere also suppresses rainfall. Under normal circumstances, we have a warm atmosphere and an upper atmosphere. Normally, hot air would rise, and it cools and forms clouds, and there would be an exchange between the upper atmosphere and the lower atmosphere, but with El Niño it injects added heat into the atmosphere, so you get a warm lower atmosphere and warm upper atmosphere, so you don’t get an exchange to drive rainfall activity.”
Coupled with the El Niño, Saharan dust also contributes to the drought conditions being faced in the Federation and the region.
“The Saharan dust that comes from the African continent not only reduces air quality but also reduces rainfall amounts. Picture this: you have a puddle of water on the ground; if you were to throw dirt on it, the dirt would absorb the water. Similarly, in the atmosphere, the dust coming through would absorb the little moisture that is in the air, thus preventing any rainfall activity. The haze reduces visibility, and it also affects persons with respiratory illnesses and other allergies.”
Incursions of Saharan dust often begin ramping up in April and May as trade wind patterns shift, with the heaviest and most frequent concentrations occurring across June, July, and August, driven by vigorous African easterly waves and the formation of the Saharan Air Layer (SAL).
Plumes begin to fade and retreat southward or eastward by late August into September and October, coinciding with shifts in major tropical weather drivers.
Despite El Niño and the Saharan dust, the threat of the Atlantic hurricane season persists.
“The drought forecast does not change the threat of hurricanes. The drought forecast is just a forecast to identify that we are expecting less rainfall than normal. The Atlantic Ocean still is warmer than normal, so there is energy within the sea. The El Niño conditions just kind of lessen the chance for hurricane development. A hurricane could still develop, and all it takes is one hurricane to come through and cause devastating impacts.”
The wet season, traditionally running from June to November, is becoming shorter, with the total annual rainfall decreasing; rainfall that does occur is delivered in shorter, incredibly intense bursts.
A distinct “Heat Season” spanning from April/May to October has intensified, effectively locking in high-humidity heat that overlaps and suppresses the early rainfall of the traditional wet season.
Multi-year climate anomalies dramatically warp the seasonal baseline. Severe El Niño events trigger extreme, unseasonable drought across the region during peak summer, extending arid conditions straight through into the following year’s climatological dry season.
