Tropical Storm Erin is expected to become a hurricane later today, Aug. 15, and a Category 4 hurricane with maximum sustained winds of 130 mph over the weekend. A major hurricane is a Category 3 or stronger, with maximum sustained winds of at least 111 mph.

Tropical Storm Erin is continuing to pick up strength as it moves across the Atlantic, with forecasters expecting the storm to officially strengthen into a hurricane on Friday, Aug. 15, according to the National Hurricane Center.

Tropical Storm Erin is still expected to become the first hurricane of the season this week as a new threat in the Gulf of Mexico emerges. Here's what to know.