Climate

The climate of Jamaica is mainly sub tropical or tropical maritime. The most important broad-scale climatic influences are the North East Trade winds and the islandŐs orographic features, (mainly the central ridge of mountains and hills). Other influences are the warm waters of the Caribbean Sea, as well as synoptic weather systems, primarily the Azores-Bermuda high-pressure system, surface, mid and upper level troughs, frontal systems, easterly waves, tropical depressions, tropical storms, hurricanes and infrequently, the inter-tropical convergence zone. Apart from diurnal changes, rainfall is the dominant meteorological variable that influences the meso-scale fluctuations of temperature, humidity, sunshine and evaporation. Similar to all the other countries of the Caribbean, Central America and the Southern and Eastern sections of the United States Jamaica is impacted from time to time by severe tropical weather systems including tropical waves, tropical depressions, tropical storms and hurricanes. The official hurricane season is from June to November, although cyclones have occurred outside this period. El Nino Southern Oscillation Effect (ENSO) is superimposed on this system and leads to regular fluctuations on a 5 to 7 year timeframe.

Rainfall is the most important climatic factor in the watershed. Three rainfall zones can be recognised: A long dry season with more than 6 months with less than 100 mm of rainfall per month. This situation applies to the coastal area and extends southward to the latitude of Perth Town. Annual rainfall in this zone is less than 1270 mm. A moderate dry season with 3 to 5 months of less than 100 mm rainfall per month. The annual rainfall is between 1270 and 1900 mm. This zone covers the Dry Harbour Mountains and Queen of Spain Valley. A short dry season with 2 to 3 months of less than 100 mm of rainfall per month. The annual rainfall is from 1900 to 2540 mm. This zone embraces the Cockpit Country and a small area south of Ulster Spring Zones


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