(CNN) -- Tropical Storm Andrea is expected to drench the East Coast with heavy rains Friday as its strength weakens.
A broader swath of the East Coast -- including parts of 13 states, from Georgia to Maine -- is under flash-flood watches. Flash flood warnings extend from Florida through coastal communities north to Virginia.
The warning means a sudden deluge of rain could overwhelm sewers, and cause rivers and creeks to overrun their banks through the weekend.
The watch area includes Washington, which the National Weather Service predicts could get up to 6 inches of rain Friday, and New York City, where forecasters say 1 to 2 inches of rain an hour could fall at times into Saturday.
Even Maine's coast, including Portland, could see as much as 3 inches of rain by the time the weekend is done.
By early Friday, Andrea was centered about 65 miles south southwest of Savannah, Georgia. It had maximum sustained winds of 45 mph, according to the National Hurricane Center.
Andrea chugged inland over northern Florida on Thursday night with wind and rain bands "spreading northward well ahead of the center," the Miami-based center reported.
The projected path is similar to Tropical Storm Debby nearly a year ago. Debby dumped up to 2 feet of rain onto the low-lying region, causing extensive flooding in some coastal towns.
"The combination of a storm surge and the tide will cause normally dry areas near the coast to be flooded by rising waters," the hurricane center warned.
CNN meteorologists Sean Morris and Ivan Cabrera contributed to this report.