Explainer: Why Monday’s rains were worse than Sunday’s

Many Jamaicans were caught off guard on Monday when they woke up to thunderstorms from a tropical weather system that had moved well southwest of the island.

Although the Meteorological Service had issued a flash flood warning for some eastern and southcentral parishes that was in effect until 5 p.m. on Monday, the discontinuation of the tropical storm watch on Saturday, coupled with largely underwhelming showers on Sunday, caused many to believe the island had escaped unscathed.

So what happened between Sunday night and Monday morning?

Ian became a hurricane

Ian, which had steadily progressed from a depression to a tropical storm, morphed into a hurricane early Monday morning.

At 7 p.m. Jamaica time on Monday, the hurricane had maximum sustained winds of 100mph and was moving north-northwest at 13mph.

With its strength intensifying throughout the day, its outer bands became more organised.

“A storm is not a dot. It is hundreds of miles wide and we are within the hundreds of miles wide. A satellite image will show you that there is a front and a back of the storm. We are caught in the back of the storm,” said Parris Lyew-Ayee Jr, executive director of the Mona GeoInformatics Institute who has a doctorate in geography.

“With the hurricane, the winds are moving faster, the air is moving upwards stronger, and so the thunderstorms can be more vigorous,” Dr Lawrence Brown, head of the Meteorological Centre, said in a Gleaner interview.

Why were southcentral, southeast regions worst hit?

The heavy rains mainly affected southern parishes despite forecasts of Ian’s westward trajectory. Its outer bands spin counterclockwise, causing, with that motion, southern and southeastern parishes to suffer the brunt of the thunderstorms on Monday.

When will the heavy rains end?

As the system moves away from Jamaica to Cuba and Florida, heavy rainfall here will eventually ease as the spiral bands cease having an effect.

“It will gradually decrease by tomorrow (Tuesday) into Wednesday. By the afternoon tomorrow (Tuesday), all the clouds and moisture associated with the system will be farther away from us,” Brown said.