Tropical Storm Tammy formed just off the Florida coast today and could bring heavy rainfall, strong winds and isolated tornadoes to northern Florida and parts of Georgia and the Carolinas in the next 24 hours, the National Weather Service said.

The storm also could bring much-needed rain to the Washington area Friday and into Saturday, said Brian Guyer, a local meteorologist for the National Weather Service.

"We need some good rain here," Guyer said. "And it's likely we'll get it by Friday. How much rain is the question."

In its latest advisory, issued at 11 a.m. EDT, the National Weather Service said Tammy, located about 40 miles northeast of Cape Canaveral, was moving northward at around 14 mph, packing winds of near 40 mph with higher gusts.

"Most of the strong winds and heavy rains are located well to the north and east of the center of circulation" of the storm, the weather service said in its advisory.

Meteorologists predicted that the forecasted movement of the storm would keep the worst of the weather offshore.

A tropical storm warning has been issued for Cocoa Beach, Fla., to Santee River, S.C., meaning tropical storm conditions can be expected through the area for the next 24 hours.

Rainfall was expected to be 3 to 5 inches in most areas with some isolated areas getting between 8 to 10 inches. High tides were expected to be 2 to 3 feet above normal and tornadoes were also possible.

Tammy is the 19th named storm of the Atlantic hurricane season, which goes from June 1 to Nov. 30.