US forecasters warn that Tropical Storm Dorian could reach hurricane strength by the time it passes Puerto Rico's southwestern coast on Wednesday.
Puerto Rico has mobilised thousands of federal agents ahead of what threatens to be the first hurricane to lash the US territory since it was ravaged by Maria in 2017, authorities said Tuesday.
US forecasters warn that Tropical Storm Dorian could reach hurricane strength by the time it passes the island's southwestern coast on Wednesday.
The Federal Emergency Management Agency said some 3,000 agents had been deployed and were "ready to respond."
"Emergency communications, logistics & transportation teams are also positioned on the island," it said on Twitter.
In September 2017, Hurricane Maria went from one end of Puerto Rico to the other, leaving a trail of destruction from which it has yet to recover.
After nearly a year of controversy, health authorities put the official death toll at 2,975, supplanting the Puerto Rican government's longstanding figure of 64.
"Wow! Yet another big storm heading to Puerto Rico. Will it ever end?" US President Donald Trump said in a tweet.
He posted that US aid approved for the island last year was a record $92 billion – "an all time record of its kind for 'anywhere.'"
In fact, Congress has allocated $42.5 billion to disaster relief for Puerto Rico, according to FEMA's website, but the island has received less than $14 billion.
Puerto Rico's new governor, Wanda Vazquez, declared a state of emergency and said the island was better prepared this time to respond to any contingency.
"In the face of the approaching situation, the response of the government and the different agencies will be different because it is prepared," she said at a news conference.
Former governor Ricardo Rossello was forced to resign last month in part because of criticism of his handling of the emergency created by Maria.
As of 1700 GMT, Dorian was packing winds of 50 miles (85 kilometers) per hour as it moved into the Caribbean through the northern Windward Islands and the southern Leeward Islands, the National Hurricane Center in Miami said.
It was about 80 miles west of Dominica and moving northwest at 13 miles per hour.
A hurricane watch is also in effect for the Dominican Republic. In Santo Domingo, residents of neighborhoods bordering the Ozama River, which crosses the capital city, are prepared to evacuate in case of flooding.
"We're ready to leave, because when it rains here, the river fills and everything floods," said Cornelia Diaz.
"But we're scared to leave our things, not because of the water but because of criminals," she said.
After passing Puerto Rico, the storm is expected to reach northeastern Dominican Republic by Wednesday night and then the Bahamas and Turks and Caicos Thursday and Friday.
Forecasters calculate that it will reach the east coast of Florida by the weekend, but say it is too early to tell how powerful it will be at that point.
It could weaken as it passes over mountainous terrain on the island of Hispaniola, which is shared by the Dominican Republic and Haiti. Or it could gain strength due to the high temperatures in the Caribbean.
The NHC said hurricane watches were in effect for Puerto Rico and the Dominican Republic, while Martinique was under a tropical storm warning.