Expats can just blame the zone for those heavy afternoon downpours

Most expats never have heard of the Inter-Tropical Convergence Zone, but that is what is getting the blame for afternoon thundershowers.

The Instituto Meteorológico Nacional said that the active zone is coming close to the country and that this will bring sometimes heavy rains today along the Pacific coast and in the Central Valley during the afternoon. The storms will be accompanied by lightning, the institute said.

That was pretty much the case Thursday when pockets of thunderstorms created by the warm and humid morning marched through parts of the valley. The location and amount of rain was highly variable.

The U.S. National Weather Service says that the convergence zone is a band of clouds consisting of showers, with occasional thunderstorms, that encircle the globe near the equator. The zone follows the sun in that the position varies seasonally, and it moves north in the northern summer and south in the northern winter, the weather service said.

The zone is where the northern trade winds and the southern trade winds meet and force the air up higher. Sailors used to call the zone the doldrums because sometimes there is little air movement and sailing ships wold be becalmed.

The weather institute predicts another hot and humid morning today, perfect condition for the predicted afternoon storms.

The institute issued a warning bulletin at 10:30 a.m. Thursday  The message noted that temperatures had approached 30 C or about 86 F in the Central Valley and higher along the Pacific coast. The institute noted that heavy rains could provoke slides and cause local flooding.

As it turned out the rains did not reach the 30 to 65 millimeters or up to 2.5 inches, that was predicted. At best, the institute’s automatic weather stations showed the heaviest rainfall to be about 8 millimeters or a bit more than a third of an inch in a section of Heredia.

Graphic shows how the zone changes location in the Western Hemisphere depending on the time of year.

Graphic shows how the zone changes location in the Western Hemisphere depending on the time of year.

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