MIAMI (AP) The fate of Florida hinges on when and how Hurricane Irma makes a right turn.
National Weather Service Director Louis Uccellini says forecasters have no doubt the powerful storm will turn in the days ahead.
If it's an early, sharp turn, Irma is more likely to keep closer to the peninsula's eastern shore or even over water as it churns north, but if it turns later and more widely, the center of Irma and its maximum destructive capacity would move inland.
Jeff Masters, the meteorology director of Weather Underground, says the main factor determining the turn will most likely be a low pressure system expected to develop over the Great Lakes as part of a dip in the jet stream, with some extra help from winds flowing out of the newly formed Hurricane Katia.
Late Thursday afternoon, Irma was centered about 40 miles south of Grand Turk Island with top sustained winds of 175 miles per hour.
Forecasters say the extremely dangerous Category 5 hurricane is moving west-northwest at 16 miles per hour.
South Florida officials are expanding evacuation orders as Hurricane Irma approaches, telling more than a half-million people to seek safety inland.
Miami-Dade Mayor Carlos Gimenez has announced evacuation orders for downtown Miami and other parts of the city, plus southern parts of the county.
The expanded evacuation area also includes Homestead, Coral Gables, South Miami, Miami Shores and North Miami Beach.
County officials had already ordered evacuations Wednesday for Miami Beach and the other barrier islands.
The total population for the affected communities is nearly 700,000 people, though the evacuation zones don't always include entire cities. Miami-Dade County's population is about 2.7 million.
Florida Gov. Rick Scott has a stark warning for anyone who wants to defy a mandatory evacuation order ahead of Hurricane Irma.
He says: "If you live in any evacuation zones and you're still at home, LEAVE!"
Scott said he "cannot stress this enough. Do not ignore evacuation orders. You rebuild your home ... you cannot recreate your family."
And this: "Do not try to ride out this storm," he says. The time to leave is now, because he says "we can't save you once the storm hits."
Thursday afternoon the eye of Hurricane Irma was moving west-northwest off the Dominican Republic's northern coast as an extremely dangerous Category 5 storm.
The U.S. National Hurricane Center said Irma has top sustained winds near 175 miles per hour and is expected to continue moving between Hispaniola and the Turks and Caicos in the afternoon hours, on a course taking it to the southeastern Bahamas Thursday evening.
A hurricane watch was in effect Thursday for the Florida Keys and parts of South Florida.
The Hurricane Center has predicted that Irma will remain at Category 4 or 5 for the next day or two as it passes the Turks and Caicos, parts of the Bahamas by Thursday night, and skirts Cuba on Friday night into Saturday.
It will then likely head north toward Florida, where people were rushing to board up homes, fill cars with gasoline and find a route to safety.
Scott says the state is doing all it can to relieve fuel shortages and traffic jams to keep people evacuating ahead of Hurricane Irma.
Scott is acknowledging that empty pumps, long lines and crowded highways are "frustrating" for Floridians.
But he says his administration is working with federal authorities and other states to move as much gas into Florida as they can.
This includes having the Florida Highway Patrol escort fuel trucks through any traffic.
Florida Highway Safety spokeswoman Beth Frady says troopers escorted trucks from two Florida ports to stations in Marion and Martin counties overnight, and also were escorting trucks from Georgia to stations in Perry, in north central Florida near where Interstate 75 crosses Interstate 10.
Irma is flooding parts of the Dominican Republic as it roars by just off the northern coast of the island it shares with Haiti.
Officials said about 500 tourists in the Bavaro-Punta Cana area were moved to more secure shelters just ahead of the Category 5 storm.
Civil Defense Director Rafael Carrasco says a landslide in the Samana Peninsula affected eight houses and more than 2,500 people have been evacuated.
Punta Cana airport has reopened after being closed for several hours.
Haiti's northern coast will be next, but Irma's stronger winds have yet to reach that side of the island of Hispaniola.
More than 1 million people in Puerto Rico are without power, nearly 70 percent of customers of Puerto Rico's Electric Power Authority.
Puerto Rican Gov. Ricardo Rossello said Thursday that crews are investigating and until they know the extent of the damage, "it will be difficult to estimate how long the power outage will last."
Rossello added that ports on the island are still closed, and it's unclear when commercial flights will resume.
Schools and government offices are scheduled to reopen on Monday.
The Dutch prime minister says Category 5 Hurricane Irma was a storm of "epic proportions" when it slammed into the former Dutch colony of Saint Maarten in the Caribbean and is appealing to Dutch citizens to donate to a relief fund set up by the Red Cross.
Speaking Thursday after a meeting of the government's crisis committee, Prime Minister Mark Rutte said there are no reports yet of casualties on the Dutch side of the island. Rutte says the damage is huge, particularly on Saint Maarten, with "wide scale destruction of infrastructure, houses and businesses."
He says, "There is no power, no gasoline, no running water. Houses are under water, cars are floating through the streets, inhabitants are sitting in the dark, in ruined houses and are cut off from the outside world."
The Dutch military is readying two aircraft to fly to the region to distribute vital aid to the shattered territory, which is home to some 40,000 people.
However the airport on the Dutch side of the island is badly damaged.
French Prime Minister Edouard Philippe says four people are confirmed dead and about 50 injured on the Caribbean island of St. Martin in the wake of Hurricane Irma.
The prime minister said one person faces life-threatening injuries and two others were in serious condition.
The death toll was lower than one given earlier Thursday by France's interior minister, who said eight people had been killed on French Caribbean territories.
Philippe said four bodies have been found on St. Martin and are being identified.
The island is part French, part Dutch, and Dutch authorities have not reported any casualties.
An official in Philippe's office said only four people are currently confirmed dead so far after a re-evaluation of the damage Wednesday. The official said the toll could rise as rescuers reach the scene. Philippe says large amounts of aid and equipment are en route to St. Martin and nearby St. Barts.
Britain is sending hundreds of troops and the Royal Navy flagship HMS Ocean to its overseas islands battered by Hurricane Irma.
Britain has already sent one ship, RFA Mount Bay, to Anguilla, which took the full force of the storm.
Defense Secretary Michael Fallon said Thursday he had ordered HMS Ocean to head to the Caribbean from the Mediterranean. Fallon also said the U.K. was sending "a task group of several hundred troops, marines, engineers and additional helicopters."
British authorities are being criticized for being slow to send aid to territories in the storm's path, but Fallon said "we are going to make sure the islands get the help they need."
Irma has hit the British territories Anguilla, Montserrat, the British Virgin Islands and Turks and Caicos.