CHARLESTON, S.C. (AP) — Tropical Storm Cristobal churned off the Southeast seaboard after it formed Saturday, the first storm to threaten the U.S. this hurricane season, forecasters said.

The storm strengthened from a tropical depression, generating maximum sustained winds of 40 mph as it promised to bring much-needed rains to the parched eastern Carolinas.

At 2 p.m. EDT, the center of the storm was about 100 miles east of Charleston and about 225 miles southeast of Cape Hatteras, N.C. The National Hurricane Center said Cristobal was moving northeast at about 7 mph.

Although the center of the storm was forecast to remain off the coast through the weekend, tropical storm warnings were in effect from the South Santee River in South Carolina to the North Carolina-Virginia state line, including Pamlico Sound.