Significant Rainfall Deficits Across Much of the Caribbean

25 04 2015

Dale C. S. Destin|

Rainfall totals across most of the Caribbean has been lower than normal for various time intervals going back a year. For some islands, rainfall deficits have been at or near record levels.

The time interval that shows the greatest deficits is the past 12 months (April 2014 to March 2015); while, over the past three months, there have been some improvements.

One way of expressing rainfall is by way of the standard precipitation index (SPI) and most of the Caribbean has been having negative values which translate to below average rainfall.

Basically, the SPI is an expression of how far away the rainfall was from the average. Positive values of 0.5 or greater (blues on the maps) indicate more rainfall than normal and negative values of -0.5 or less (yellows & reds on the maps) indicate lower than normal rainfall.

By general definition, all areas with an SPI of minus 0.5 or less are experiencing drought. This includes the Virgin Islands to Martinique. Hence, most of the northeast Caribbean is in drought, of some kind. According to the Caribbean Drought Bulletin, drought also exists across Eastern Jamaica and Haiti.

2015 first-quarter rainfall

Lower than normal first-quarter rainfall has not only been experienced by Antigua but also by most of the rest of the Leeward Islands, the Virgin Islands and the Windward Islands north of St. Lucia, according to the graphic (click for larger view) from the Caribbean Institute for Meteorology and Hydrology (CIMH).

SPI for Jan-Mar2015

Credit: @CIMHbb

First-quarter deficits were most extreme across St. Martin and nearby islands such as Saba and St. Barthelemy; the rainfall totals were at record low levels or in the bottom 2% of all totals for January-March.

Surplus rainfall took place across parts of Puerto Rico and the Dominican Republic; rainfall totals were at record high or in the top 5% of all rainfall for this time of the year.

Rainfall for the past six months

Over the past two quarters (October 2014-March 2015), more areas than the first-quarter experienced significant rainfall deficits. The “bullseye” dry spot remained over Dominica, where rainfall totals were in the bottom 5% of the historical record.

SPI Oct2014-Mar2015

Credit: @CIMHbb

Nearby islands – Guadeloupe, Dominica and Martinique, had rainfall totals ranked in the bottom 10% of the historical record.

Meanwhile, Tobago enjoyed surplus rainfall with totals in the top 10% for this period.

Rainfall for the past year

Of the three time scales, the past 12-months saw the greatest area under significant rainfall deficits.  A “bullseye” dry spot is again evident over Dominica; rainfall deficits were near record high levels.

SPI for Apr2014-Mar2015

Credit: @CIMHbb

Rainfall totals were also ranked in the bottom 10 percent for Guadeloupe, Dominica, Martinique and parts of St. Lucia.

Coastal areas of parts of Guyana, Puerto Rico and Jamaica had surplus rainfall.

The Cause

Much of this dry weather is due to the presence of El Nino and a positive North Atlantic Oscillation (NAO). Both phenomena are known to suppress rainfall activity across most of the region.


According to CariCOF, the outlook is for most areas for April-June is for above normal rainfall which would ease the deficits. However, with El Nino developing and SSTs cooling in response to the positive NOA, the long term outlook is for the increase and spread of rainfall deficits.

Increasing rainfall extremes, mainly deficits, are likely to increase across the region once El Nino develops and persists. It is likely to be a drought year for much of the Caribbean; how bad would depend on the eventual duration and strength of El Nino and how cool the Atlantic gets.

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