(Bloomberg) -- Heavy rains are poised to pummel South Florida this week, threatening to unleash flooding in cities including Miami, Fort Lauderdale and West Palm Beach.

Moisture from the Gulf of Mexico will wring itself out across southern Florida through the rest of the week, with rain falling at rates of up to 3 inches (7.6 centimeters) per hour, said Peter Mullinax, a meteorologist with the US Weather Prediction Center.

Through just Wednesday, 6 to 9 inches of rain is forecast for the region, where flood watches have been posted, according to the National Weather Service. The pattern will continue at least through Friday, making the situation worse each day. Thunderstorms could bring isolated downpours and high winds.

“It will be a pretty active stretch,” Mullinax said. The amount of moisture flowing off the Gulf “even for Florida standards is pretty high.”

Florida is in peril because of larger weather patterns across the US and Caribbean, Mullinax said. High-pressure systems across the Great Plains and the Lesser Antilles in the Caribbean have pinned a trough of low pressure across Florida. This has allowed long plumes of moisture to flow out of the Gulf and across the state.

“The trough has nowhere to go for a few days,” Mullinax said.

The storms raining down across Florida are expected to move into the Atlantic off the East Coast later in the week, the US National Hurricane Center said. There is a 20% chance they could coalesce into the season’s first tropical system, which would be named Alberto, in the next seven days. 

--With assistance from Cedric Sam.

(Updates with tropical storm forecast in seventh paragraph.)

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