Still Off Florida's Coast, Tropical Storm Arthur Moves Northward : The Two-Way Arthur is the first tropical storm of the Atlantic hurricane season. It's forecast to become a hurricane by Thursday.

Still Off Florida's Coast, Tropical Storm Arthur Moves Northward

Tropical Storm Arthur spins off the coast of Florida. NOAA hide caption

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Updated 3:30 a.m. ET Wednesday:

Forecasters at the U.S. National Hurricane Center In Miami say Tropical Storm Arthur is gaining strength as it moves slowly northward. Early Wednesday morning, the storm was about 95 miles off the coast of Cape Canaveral. Its maximum sustained winds had increased to about 60 mph.

Original Post:

The first tropical storm of the Atlantic season has formed off the coast of Florida and is threatening the Carolinas.

The National Hurricane Center is forecasting tropical storm Arthur to become a hurricane by Thursday and continue hugging the U.S. coast before moving northeast.

The Washington Post's Capital Weather Gang explains:

"During the day on Thursday we can expect a strong tropical storm off the South Carolina coast, then a possible landfall as a minimal hurricane early Friday morning near the Outer Banks of North Carolina. From there, it remains offshore, cruising by the Mid-Atlantic area and Delmarva peninsula during the day on Friday.

"The bulk of the rain from this system will remain offshore through Friday, with the exception of coastal areas of FL, GA, SC, NC and possibly the Delmarva – depending on the storm's exact track. The North Carolina Outer Banks are most vulnerable to hazards from this storm and are likely to contend with heavy rain, tropical storm-force winds and some coastal flooding Thursday night into Friday morning."

At the moment, the National Hurricane Center says Arthur is drifting to the northwest with sustained winds of 50 mph. The Hurricane Center has also posted a tropical storm watch along the east coast of Florida from Fort Pierce to Flagler Beach.