Tropical Storm Karen stationary over Gulf of Mexico

(CNN) -- Its winds no longer a major threat, a stalled Tropical Storm Karen still carried the threat of storm surge to portions of the U.S. Gulf Coast.

The National Hurricane Center (NHC) said the storm's maximum sustained winds were at 40 mph on Saturday evening.

The storm was idle much of Saturday night, but forecasters predicted it would turn northeast and gain speed going into Sunday, when it was expected to weaken to a tropical depression.

The center of the storm will move just south of the Gulf Coast from Alabama to the Florida Panhandle on Sunday night and Monday, the NHC predicted. The storm will dissipate into a remnant area of low pressure on Sunday evening, with no secondary landfall along the northern Gulf Coast, forecasters said.

A tropical storm warning was in effect for Grand Isle, Louisiana, to the mouth of the Pearl River.

Coastal residents were warned that storm surges and dangerous waves remained possible.

The storm is expected to drop up to 3 inches of rain over parts of the central and eastern Gulf Coast through Sunday night, mainly near and to the east of the storm's center, the hurricane center said.

Storm surges also are a concern. If peak surges coincide with high tide, water could reach up to 3 feet above ground from the mouth of the Mississippi River in Louisiana to Alabama's Mobile Bay, the center said.

"The combination of storm surge and the tide will cause normally dry areas near the coast to be flooded by rising waters," the center said.

CNN's Sean Morris, Eliott C. McLaughlin, Todd Borek and David Simpson contributed to this report.