Hurricane Erin has catapulted in strength, turning into a monstrous Category 5 hurricane at one point on Saturday, before weakening slightly back to Category 4.

The powerhouse storm had explosively intensified overnight into Saturday, after becoming the Atlantic season’s first hurricane by Friday midday.Earlier in the day, the storm had intensified at triple the rate needed to classify as rapid intensification, which is when a storm’s wind speeds increase by at least 35 mph in 24 hours.

As of earlier Saturday, the National Hurricane Center warned the storm’s outer bands were beginning to affect the Northern Leeward Islands. A tropical storm watch remains in effect for St. Martin, St. Barthélemy and Sint Maarten, but the storm should largely spare the Lesser Antilles. Puerto Rico could see a few rain showers, blustery winds or squally weather Saturday afternoon and evening, but the storm will pass well to the north of the U.S. territory.

From there, Erin was expected to remain a dangerous major hurricane as it curves northward between the Southeast U.S. and Bermuda early next week.