Regional variations of the Caribbean mid-summer drought

Pentad satellite-based precipitation estimates were input into a wavelet analysis to quantify the length, timing, and strength of the mid-summer drought (MSD) for the Caribbean Sea and surrounding regions. For most of the Caribbean the time between the first and second summer precipitation maxima is 98 to 117 days (similar to 3 to 4 months). The MSD appears in early-June over Puerto Rico and Hispaniola, and develops progressively later in the summer season towards the west, finally occurring in early-October over the Gulf of Mexico. The MSD is most intense in the eastern Pacific, strong and significant in the western Caribbean, and almost nonexistent in the eastern Caribbean. Forcing mechanisms are examined to help explain the regional variability in the Caribbean. A July increase in surface pressure and surface divergence, caused by the changing wind field, appears to contribute to a strong concurrent MSD over the waters bounded by Jamaica, Cuba, and the Yucatan peninsula. Finally, the island of Jamaica itself appears to block the flow of the tradewinds as they migrate northward and intensify into mid-summer, thus enhancing the divergence, and in turn MSD, immediately to the west.