Tropical Storm Ernesto expected to strengthen into a hurricane in the Atlantic

Tropical Storm Ernesto is expected to strengthen into a hurricane Tuesday night, according to the National Hurricane Center.

Ernesto was in the Caribbean on Tuesday afternoon, about 135 miles east-southeast of Puerto Rico, and moving west-northwest at 18 mph with 60 mph maximum sustained winds.

The tropical storm is expected to become a hurricane while passing northeast of Puerto Rico, according to the National Hurricane Center.

The center of Ernesto should pass near or over the Virgin Islands Tuesday night and then pass to the northeast and north of Puerto Rico Tuesday night and on Wednesday, the hurricane center said.

The storm is expected to turn toward the northwest Tuesday night with a gradual decrease in its forward speed. The storm will then turn toward the north-northwest and north Wednesday night and Thursday, according to the hurricane center.

"On the forecast track, the center of Ernesto should pass near or over the Virgin Islands this evening, and then pass just to the northeast and north of Puerto Rico tonight and on Wednesday," the hurricane center said Tuesday morning.

In a news conference Tuesday, Puerto Rico Gov. Pedro Pierluisi urged people to not leave their homes after 6 p.m. because storm conditions are expected to worsen on the U.S. territory by midnight. Officials also anticipated widespread power outages across the island as Puerto Rico's electric grid has not been permanently rebuilt since Hurricane Maria razed it in 2017.

Vieques and Culebra, the island-municipalities about 7 miles off Puerto Rico’s eastern coast, are under hurricane warning, said Ernesto Rodríguez, director of the National Meteorological Service in San Juan, during the conference.

"We must not let our guard down," Rodríguez said.

A hurricane watch was also issued for the U.S. and British Virgin Islands as most of Puerto Rico remained under tropical storm warning Tuesday afternoon.

The storm will move across the western Atlantic later in the week.

The storm will continue strengthening over the next few days and is expected to become a hurricane just north of the Greater Antilles — which includes Cuba, Puerto Rico and Jamaica — by Thursday.

Tropical storm conditions are expected to affect the Virgin Islands in a few hours, the hurricane center said in a Tuesday afternoon update.

Ernesto may bring 4 to 6 inches of rain to parts of the Leeward Islands and Virgin Islands and up to 10 inches of rain across southeastern Puerto Rico, according to the hurricane center.

Water levels may increase by up to 3 feet above ground level on the east coast of Puerto Rico, as well as for the U.S. and British Virgin Islands. Large and destructive waves may accompany the storm surge near the coast of the British Virgin Islands.

Puerto Rico has already activated the National Guard and canceled the start of classes in public schools, The Associated Press reported.

Tropical storm warnings have been issued for St. Kitts and Nevis, St. Martin and St. Maarten, Puerto Rico, St. Barts, Saba and Sint Eustatius.