The National Weather Service extended a flood warning for most of Broward County and all metropolitan Palm Beach County through Tuesday evening.

Forecasters said the atmosphere remained moist from Isaac and more conducive to firing up afternoon thunderstorms — and that could slow drainage in impacted areas, particularly in central Palm Beach County, the wettest spot in South Florida after Isaac dumped some 18 inches of rain over two days.

Many streets and yards in the communities of Wellington, The Acreage and Loxahatchee remained underwater Tuesday. It was bad enough that the Palm Beach County School District decided to leave eight schools in the area closed for another day while the rest of the public schools in the county prepared to open Wednesday.

Gauges in Northeast Broward recorded more than 11 inches of rain and from five to eight inches fell along the South Florida coast from Homestead to Jupiter.

Robert Molleda, a weather service meteorologist, said West Palm Beach set a two-day record for rainfall with just over nine inches on Sunday and Monday — making it the all-time soggiest August there — with a record 22.28 inches of rain. That broke a 1995 record of 20.12 inches.

In Pembroke Pines, public works crews spent Monday and Tuesday removing storm debris from street drainage grates, and cleaning up fallen trees and palm fronds but found only isolated street ponding.

“Not anything I would call significant flooding,’’ said Shawn Denton, public works director. “It was random — some random streets where swales or drains got clogged. In some cases, we had to shovel it out.”

On the positive side, Isaac’s rain helped refill Lake Okeechobee, with lake levels rising three-quarters of a foot in just two days.

Water flowing into the lake was 10 times the volume of a week ago, the South Florida Water Management District reported. The lake stood at 13.12 feet above sea level on Tuesday and was expected to continue to rise for several days as storm runoff drains south.

Miami Herald staff writers Daniel Chang and Carli Teproff contributed to this report.