Hurricane Erin has been downgraded to a Category 3 hurricane but is gaining in size and raising the risk of life-threatening surf later this week along the U.S.

Tropical Storm Erin is still moving quickly westward and is forecast to become a hurricane in a few days over the central tropical Atlantic, the NHC said.

Implications for the Leeward Islands: Residents and visitors in St. Thomas, St. John, St. Croix, Puerto Rico and the northern Leeward Islands should monitor this system throughout the week. Even if the wave remains weak, increased moisture could bring showers, gusty winds and higher seas toward the end of the week.

Storms that ramp up so quickly complicate forecasting and make it harder for government agencies to plan for emergencies. Hurricane Erick, a Pacific storm that made landfall June 19 in Oaxaca, Mexico, also strengthened rapidly, doubling in intensity in less than a day.

Powerful Hurricane Erin is expected to bring high seas, big rip currents, and rough surf as it moves between the United States and Bermuda.