Some aspects of Puerto Rican rainfall

Abstract

Rainfall in Puerto Rico during the dry season (roughly December to April) varies markedly from year to year. In preliminary studies directed toward development of seasonal forecasting methods, the precipitation records have been analyzed to determine the synoptic types favorable for different seasonal rainfall totals during the months January to March, inclusive. Synoptic studies indicate that days with 0.25 inch or more of rainfall are usually the result of major synoptic disturbances, and that days with 0.20 or less represent undisturbed atmospheric flow with frequent light showers. An analysis of over 40 years of record on this basis shows that most of the heavier precipitation of the dry season is accounted for by major synoptic disturbances. Seasons of deficient rainfall tend to have a high frequency of days with 0.20 inch or less of precipitation; this correlation is appreciably greater than with the number of days having no rainfall.The data presented here are principally for San Juan on the north coast and Mayagüez on the west coast. Results obtained for both stations are in agreement, but correlation of rainfall between the two stations is not very good, indicating that, for forecast purposes, the effects of the broad‐scale circulation patterns must be correlated separately for different stations or areas.