One of the greatest problems facing weather forecasters is the prediction of heavy rainfall and associated flash floods. Forecasting in the tropics presents a greater challenge especially for small islands like Jamaica. In the absence of comprehensive data and routine observations, researchers and forecasters must rely on case studies to increase our understanding of excessive precipitation events.
Environmental conditions associated with two heavy rainfall episodes (3-4 January and 3-4 March 1998) are presented. These events resulted in six deaths and severe property damage in Jamaica. The cases are unusual in that they occurred during what is normally the dry season for most of the Caribbean (January - March). The first event produced a maximum of 425mm of rain in Port Antonio during the two day period; twice the normal total for the entire month of January for that area. Analyses of flash floods in Puerto Rico and Hawaii illustrated several features that are applicable to Jamaica. These include orographic forcing and very moist conditions created by a stalled frontal system that resulted in intense convection and heavy precipitation over northeast Jamaica.
In addition to investigating the characteristics of individual precipitation events, this study also examines the regional climatic controls such as Caribbean sea surface temperatures, surface pressure anomalies, and El Niņo/Southern Oscillation (ENSO). The advent of a strong ENSO episode resulted in moisture-laden winter cyclones and associated fronts that moved along a more southerly track than previous years. The results of these case studies can be used to develop new algorithms and procedures for forecasters in the tropics.