The St Barts Caribbean climate is tropical, moderated to a certain extent by the prevailing northeast trade winds. Individual climatic conditions are strongly dependent on elevation. At sea level there is little variation in temperature, regardless of the time of the day or the season of the year. Temperatures range between 24°C and 32°C. In Kingston, Jamaica, the mean temperature is 26°C, whereas Mandeville, at a little over 600 meters high in the Carpenters Mountains of Manchester Parish, has recorded temperatures as low as 10°C. Daylight hours tend to be shorter during summer and slightly longer during winter than in the higher latitudes. The conventional division, rather than the four seasons, is between the long rainy season from May through October and the dry season, corresponding to winter in the northern hemisphere.
Even during the rainy period, however, the precipitation range fluctuates greatly. Windward sides of islands with mountains receive much rain, whereas leeward sides can have very dry conditions. Flat islands receive slightly less rainfall, but its pattern is more consistent. For example, the Blue Mountains of eastern Jamaica record around 558 centimeters of rainfall per year, whereas Kingston, on the southeastern coast, receives only 399 centimeters. Bridgetown, the capital of Barbados, has an average annual rainfall of 127 centimeters, while Bathsheba on the central east coast receives 254 centimeters–despite the fact that Bathsheba is only about 27 kilometers away by road. Recording stations in the Northern Range in Trinidad measure some 302 centimeters of rainfall per year, while at Piarco Airport on the Caroni Plains the measurement is only 140 centimeters. Most of the rainfall occurs during short heavy outbursts during daylight hours. In Jamaica, about 80 percent of the rainfall occurs during the day. The period of heaviest rainfall usually occurs after the sun has passed directly overhead, which in the Caribbean islands would be sometime around the middle of May and again in early August. The rainy season also coincides with the disastrous summer hurricane season, although Barbados, too far east, and Trinidad and Tobago, too far south, seldom experience hurricanes.
Hurricanes are a constant feature of most of the Caribbean, with a “season” of their own lasting from June to November. Hurricanes develop over the ocean (usually in the eastern Caribbean) during the summer months when the sea surface temperature is high (over 27°C) and the air pressure falls below 950 millibars. These conditions create an “eye” about 20 kilometers wide, around which a steep pressure gradient forms that generates wind speeds of 110 to 280 kilometers per hour. The diameter of hurricanes can extend as far as 500 to 800 kilometers and produce extremely heavy rainfalls and winds.