MIAMI (CBS/AP) — The first tropical storm of the season has formed off the coast of South Carolina with top winds of 45 mph (75 kph).

Forecasters say tropical storm Alberto was centered about 140 miles (225 km) off Charleston, S.C. on Saturday afternoon.

It was moving about 3 mph (6kph) to the southwest.

Some strengthening was possible.

A forecast map by the hurricane center predicts that the storm will drift toward the open sea off the Midatlantic by midweek, but it’s difficult to accurately predict a storm’s path days in advance.

The official start to hurricane season is June 1.

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