(Introduction):

The Caribbean slope of Central America is located windward about the trade winds associated with the North Atlantic Subtropical High and the rains present a bimodal annual cycle, observing a relative minimum in the months of September and October.

(Objective):

Characterize the observed decrease in rainfall in this region for this bimester, estimating for each event, the variables associated with the values of the onset day, minimum day, demise day, duration, intensity, and magnitude, in 1979-2010.

(Methodology):

A set of 31 daily records from rain gauge stations was used. In each of them, the months from July to November were examined to find the values of the minimum, the date of the minimum, the onset and the demise, duration, and intensity. The occurrence of any temporal or spatial trend in these characteristics of the events was explored. Finally, different climatic indices and documentary sources were reviewed to identify the possible synoptic causes of the strongest decreases in rainfall.

(Results):

The beginning of the events was observed around September 3rd, their minimum on September 23rd and the end on October 12th, with an approximate duration of 39 days. Events tend to happen earlier at stations located northwest on the isthmus. The driest events occurred under favorable conditions for the occurrence of winds with a southwest-west component over the region.

(Conclusions):

Knowledge about these characteristics of precipitation helps in the activity planning of key socioeconomic sectors in Central America in case of adverse hydrometeorological events.