TAMPA, Fla. (WFLA) — As of 5:50 a.m. on Saturday, Hurricane Erin has strengthened to a Category 4 storm, NHC said.

Erin has been rapidly strengthening and is expected to continue to do so. NHC upgraded the strength of the storm from a Category 3 to a Category 4 in a special update at 5:50 a.m. on Saturday.

It’s currently around 170 miles northeast of Anguilla, a small island that’s part of the Lesser Antilles, and is moving west-northwest at around 20 mph.

A tropical storm watch is currently in effect for St. Martin, St. Barthelemy and Sint Maarten, and the NHC said tropical storm conditions are possible over the next 12 hours. The outer rainbands of the storm are already affecting the northern Leeward Islands.

With maximum sustained winds of 120 mph, Erin is sitting in the middle of the Category 3 wind speed range, which is between 111 mph and 129 mph. NHC said hurricane-force winds extend 30 miles from the center of the storm, and tropical storm-force winds extend 125 miles.

The outer bands of the storm are expected to continue lashing the northern Leeward Islands, Virgin Islands and Puerto Rico through Sunday, bringing anywhere from 2 to 6 inches of rain.

Swells generated by Hurricane Erin are forecast to spread to the East Coast of the U.S. early next week, likely causing life-threatening rip currents.

The storm is still expected to turn north early next week, skimming the Caribbean islands and Puerto Rico before changing direction.