Erin’s sustained winds increased to 70 mph, just 4 mph shy of hurricane strength. The hurricane center said Erin should continue to strengthen through the weekend, when it should be moving near or north of the Leeward Islands, according to the official forecast path.

Tropical Storm Fernand won’t make landfall, but warming Gulf waters raise concerns about stronger, less predictable storms this hurricane season.

Erin is expected to develop into a hurricane later this week and could affect Puerto Rico, the Virgin Islands and the northern Leeward Islands.