A paper entitled Seasonal Atmospheric Transitions in the Caribbean basin and Central America, led by a UWI Scientist, recently published in international journal, Climate Dynamics provides new insights into the onset and end dates of the Caribbean rainfall season.
The Caribbean has a rainfall season that roughly spans May through November with a short dry period in between. The regional agricultural sector is acutely aware of this cycle and in many countries farmers try to estimate the start and end dates of each season to maximize crop production. However, Dr Isabelle Gouirand, Climate Specialist at The UWI, Cave Hill Campus has led a study with collaborators Professor Vincent Moron from Aix-Marseille University, France and Dr Bernd Sing, also from Cave Hill, to help determine exactly when the rainy season will start and end and what atmospheric and oceanic conditions may prompt this.
Using a new methodology based on “snap shots” of daily weather types associated with either dry or wet conditions, Dr Gouirand and collaborators determined the historical transition between the dry and wet seasons in the Caribbean. They found that the average dates of transition for the 1979-2017 period occur around May 13 (+/- 9 days) for onset, and October 26 (+/- 12 days) for demise.
They also found that onset in May is rather abrupt, with a sudden increase in the daily rainfall amount over the Caribbean region, with any of a number of atmospheric and oceanic triggers capable of causing onset. In comparison, demise in October is smoother and associated with a gradual rather than a sharp decrease in the daily amount of rainfall.
An anomalously warm Eastern Pacific Ocean along with an anomalously cold Tropical North Atlantic, Caribbean Sea and Gulf of Mexico can force an earlier end of the rainy season. Importantly, onset and demise are also found to be independent. This means that a delayed or advanced onset in May does not necessarily translate into a delayed or advanced demise in October.
The paper also explores the predictability of onset, with predictability in May being low (up to two weeks before the transition) but with significantly greater predictability for the end of the season. This is of particular significance for all rainfall-dependent sectors in the Caribbean (e.g. agriculture, water, tourism etc.). If operationalised, the methodology will enable better determination of exactly when the rain will start and end.