(CNN) Beachgoers heading to the Gulf Coast this week could be greeted by the first tropical system to threaten the United States this year.

A tropical depression is expected to form late Wednesday or early Thursday from a broad area of low pressure moving slowly west over the northern Gulf of Mexico, the National Hurricane Center said.

The center upgraded the chance that the tropical depression forms within the next 48 hours from 50% to 70%.

A tropical depression is an area of thunderstorms that produces a circular wind flow with maximum sustained winds below 39 miles per hour.

If maximum sustained winds strengthen to 39 to 73 mph, the system becomes a tropical storm. And if they strengthen to 74 mph, we'd have a hurricane.

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