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by
Mr. Horace Burton, Chief Meteorologist, Caribbean
Institute for Meteorology and Hydrology (CIMH).
The Intertropical Convergence Zone
(ITCZ) is generally defined as the region near the equator where the trade
winds come together. However, meteorologists focus on the cloudiness and
precipitation and, as a result, define the ITCZ as the narrow east-west band of
vigorous cumulonimbus
clouds and heavy precipitation which forms along the equatorward boundary of
the trade wind regimes.
In general, the ITCZ migrates
north and south of the equator with the sun, but over the Atlantic and the
Eastern Pacific Oceans the zone resides predominantly in the northern
hemisphere. In the western Atlantic the ITCZ shifts from its southernmost
position just north of the equator in February and March to its most northerly
position around 10° or 11°N in August and September. The
ITCZ therefore affect the southern parts of the Caribbean and can produce
significant amounts of rainfall over these areas between June and September. The
northern parts of Guyana experience two rainy seasons as a result of the ITCZ. The
primary wet season occurs between May and July when the ITCZ is moving
northward, while the secondary wet season from November to January is associated
with the southward movement of the ITCZ.
The intensity of the ITCZ varies significantly
from one day to the other and it is not uncommon for the ITCZ to be very active
and intense one day and to disappear entirely 24 hours later. Meridional
excursions of the ITCZ are also not unusual from one day to the next. These
excursions are usually difficult to predict and present major problems for
forecasters.
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