MIAMI (Reuters) - Sub-tropical storm Ana formed off the southeast coast of the United States with maximum sustained winds of 45 miles per hour (75 km/h), the U.S. National Hurricane Center (NHC) said late Thursday.
The first named storm of the Atlantic hurricane season was located about 170 miles (275 km) south-southeast of Myrtle Beach, South Carolina, the Miami-based federal weather forecaster said.
Ana, which began drenching the South Carolina coast with heavy rain on Thursday, is likely to strengthen into a tropical storm in the next day or so with winds of 50 miles per hour (81 km/h). It should remain near or over the warm waters of the Gulf Stream, the NHC said, before weakening as it approached the coast.
A tropical storm warning was in effect from Edisto Beach, South Carolina to Cape Lookout, North Carolina.
Ana's formation is the earliest appearance of a named storm in the Atlantic since a previous incarnation of Subtropical Storm Ana on April 20 2003, said Jeff Masters, chief meteorologist for Weather Underground, a commercial weather service.
The Atlantic hurricane season runs from June 1 through Nov. 30.
The Atlantic Ocean will see a "well below average" number of hurricanes this season due to cooler Caribbean waters and a strong El Gino effect, forecasters with Colorado State University predicted in April.
(Reporting by David Adams in Miami and Arpan Varghese in Bengaluru; Editing by Paul Tait, Gopakumar Warrier and Sunil Nair)