Puerto Rico is under a tropical storm warning and a hurricane watch as Dorian approaches

(CNN) — A tropical storm warning and a hurricane watch are in effect Tuesday morning for Puerto Rico as Tropical Storm Dorian moves into the Caribbean toward the island.

The storm’s center is expected to pass near, or just south of, Puerto Rico on Wednesday afternoon and evening, with Dorian expected at that time to be a strong tropical storm, according to the National Hurricane Center.

A tropical storm warning means tropical storm conditions are expected within 36 hours, and a hurricane watch means that hurricane conditions are possible within 48 hours.

Puerto Ricans have been urged by their governor to prepare for the coming storm. Gov. Wanda Vázquez Garced on Monday declared a state of emergency for the island.

“I urge citizens to activate their emergency plan with caution and peace of mind,” Vázquez said on Twitter. “For citizens who do not yet have safe roofs, we will have shelters ready.”

There were 360 shelters open across the island for a capacity of 48,500 residents, the government’s official Twitter account said Monday. And about 70 hospitals were prepared to handle emergencies, officials said.

After passing Puerto Rico, Dorian is forecast to move near or over eastern Hispaniola and on Thursday to move north, the hurricane center said.

By the end of the week, what’s left of Dorian is expected to move toward the Bahamas and possibly into the southeastern parts of the United States. Forecasts show Dorian reaching the Florida peninsula sometime this weekend as a tropical storm.

But it’s still too early to know what the impact will be, CNN meteorologist Haley Brink said.

Where Dorian is now

Around 8 a.m. ET Tuesday, the storm was moving across the island nation of St. Lucia, with maximum sustained winds of 50 mph.

Dorian will dump heavy rain over the Windward Islands — Martinique, St. Lucia, Barbados, St. Vincent and the Grenadines, and Grenada — through Thursday. Rainfall there will generally be up to 6 inches, with some isolated downpours of up to 10 inches, the hurricane center said.

Tropical storm conditions are possible throughout the Lesser Antilles through Tuesday morning and in Puerto Rico on Wednesday, the center said.

The storm is expected to intensify as it crosses the Caribbean Sea and is forecast to be near hurricane strength when it moves close to Puerto Rico and the Dominican Republic on Wednesday and early Thursday, forecasters said.

Hurricanes have maximum sustained winds speeds of at least 74 mph.

Puerto Rico and Florida prepare

Puerto Ricans, still grappling with the devastation of Hurricane Maria in 2017, are on alert for what could be coming.

“Thankfully, I’ve been preparing since May,” said Krystle Rivera, whose family has been stocking up on water, canned food and gas in anticipation of the hurricane season.

The territory’s department of education said public schools will be open only until 1 p.m. on Tuesday, as instructed by the governor, to allow for preparations of shelters and staff, the government said.

FEMA has positioned supplies in Puerto Rico and the US Virgin Islands ahead of the storm — more than what was in place before hurricanes Irma and Maria in 2017 — Acting Administrator Peter Gaynor said.

“Four Incident Management Assistance Teams are deploying today with another on standby,” he said on Twitter.

In South Florida, more than 200 people from 30 fire departments prepared Monday to deploy into the storm’s path, CNN affiliate WPLG reported.

“In this particular situation, we’re going to be there before the storm hits, so we’ll get a little familiarized with the area that we will be responsible for,” Miami Fire Rescue Assistant Chief Scott Dean said. “We’ll weather the storm where our base of operations will be located, and then as soon as the storm goes through and it’s safe, our members will go into the streets and start operations and protect the search-and-rescue efforts.”

This is peak hurricane season

Dorian is the fourth named storm of this Atlantic hurricane season, which generally peaks in the eight weeks surrounding September 10.

Two-thirds of all the storms produced in a typical season occur during this period.

That’s because it’s the time when conditions in the tropics become prime for storm development. By the end of August, waters in the tropics have warmed, and wind shear across the Atlantic begins to weaken.

And this year, El Nino has dissipated, making conditions even more favorable for development.