The trade winds meet (or converge) in the zone of low pressure in equatorial regions. This zone is called the Inter-Tropical Convergence Zone (ITCZ). Atmospheric conditions in the ITCZ are very unstable. There are strong currents of rising air known as updraughts. As the air rises, the moisture within it condenses, clouds form and it rains. The unstable conditions in the ITCZ make equatorial regions some of the wettest in the world. These areas often experience heavy rainfall and thunderstorms.
In this photo, the ITCZ can be seen as a band of clouds over equatorial regions (photo by NASA)
The ITCZ is a very large feature which circles the globe. It affects many tropical areas around the world including territories in the southern Caribbean. The ITCZ is not stationary. It moves north of the equator during the northern hemisphere summer, bringing heavy rain to Trinidad and Tobago and Grenada. It then moves south, crossing the Equator and moving into the southern hemisphere. The ITCZ reaches its most southerly point during the northern hemisphere winter,bringing heavy rain to Brazil. The ITCZ crosses Guyana as it travels to the north and then again as it moves south, giving this country two periods of heavy rainfall each year. The map below shows the northernmost and southernmost positions of the ITCZ.
The northernmost and southernmost positions of the ITCZ (by Mats Halldin)
References
http://en.wikipedia.org/wiki/File:ITCZ_january-july.png
http://en.wikipedia.org/wiki/File:Hurricane_Bill_in_First_Full_Disk_Thermal_Image_from_GOES_14.jpg
http://geography.about.com/od/climate/a/itcz.htm
http://earthobservatory.nasa.gov/IOTD/view.php?id=703