THE RAINFALL CLIMATOLOGY OF THE BAHAMAS REVISITED: IMPLICATION FOR THE GEOSCIENCES

Over the past 15 years, precipitation data has been collected on San Salvador, Bahamas. This data collection effort is different from previous efforts in the Bahamas with duration, magnitude, and time of occurrence recorded as opposed to daily total alone. The purpose of this study is to compare and contrast this new data with findings of previous research that almost exclusively used daily and monthly totals for analysis. Previous research documents the variability in magnitude of Bahamian precipitation; particularly interannual variability. The data collected on San Salvador supports this documented interannual variability but also identifies variability in storm type and seasons. In particular, spring/early summer storms created by frontal storms contribute significant amounts to annual rainfall totals, sometimes more than tropical systems. In addition, a mid-summer dry spell is created as the North Atlantic High expands over the archipelago in May/June. Consequently, as opposed to previous research, which emphasizes one wet and one dry season per year, four rain seasons can be identified in the annual cycle: winter dry, spring wet, summer dry, and fall wet. In regard to storm type, a non-synoptic convective storm type, which received little emphasis in previous research, is an important component of the Bahamian rainfall climatology. It is hypothesized that these storms are created as warm moist air in the Trade Winds is uplifted once it passes over the warm island surface. Given the relatively small size of the island, the uplift is not dramatic but causes, small brief showers. Such storms are high frequency and low magnitude. Consequently, the small storms contribute a large portion to the annual precipitation input of the island. Given the archipelago’s high rates of evapotranspiration, much of the non-synoptic storm rainfall does not become ‘effective precipitation’ for the region’s hydrologic, biogeochemical, and resource systems. Thus, the ‘effective hydrologic input’ to these systems derived from precipitation may be much lower than the annual and monthly totals reported in previous literature.