This GOES-16 satellite image taken Wednesday, Aug. 28, 209, at 17:20 UTC and provided by National Oceanic and Atmospheric Administration (NOAA), shows Dorian, a Category 1 hurricane, crossing over the U.S. and British Virgin Islands. Forecasters say it could grow to Category 3 status as it nears the U.S. mainland as early as the weekend. (NOAA via AP)

Florida residents picked the shelves clean of bottled water and lined up at gas stations Thursday as an increasingly menacing-looking Hurricane Dorian threatened to broadside the state over Labor Day weekend.

Leaving mercifully little damage in its wake in Puerto Rico and the Virgin Islands, the second hurricane of the 2019 season swirled toward the U.S., with forecasters warning it will draw energy from the warm, open waters as it closes in.

The National Hurricane Center said the Category 1 storm is expected to strengthen into a potentially catastrophic Cat 4 with winds of 130 mph (209 kph) before slamming into the U.S. on Monday somewhere between the Florida Keys and southern Georgia—a 500-mile stretch that reflected the high degree of uncertainty this far out.

"If it makes landfall as a Category 3 or 4 hurricane, that's a big deal," said University of Miami hurricane researcher Brian McNoldy. "A lot of people are going to be affected. A lot of insurance claims."

President Donald Trump said Florida is "going to be totally ready." He tweeted: "Be prepared and please follow State and Federal instructions, it will be a very big Hurricane, perhaps one of the biggest!"

With the storm's track still unclear, no immediate mass evacuations were ordered.

National Hurricane Center Director Ken Graham, left, looks on as Florida Gov. Ron DeSantis speaks about Tropical Storm Dorian outside of the the National Hurricane Center, Thursday, Aug. 29, 2019, in Miami. (AP Photo/Lynne Sladky)

Along much of Florida's east coast, shoppers rushed to stock up on food and emergency supplies at supermarkets and hardware stores, and motorists topped off their tanks and filled gasoline cans. Some fuel shortages were reported in the Cape Canaveral area.

Josefine Larrauri, a retired translator, went to a Publix supermarket in Miami only to find empty shelves in the water section and store employees unsure of when new cases would arrive.

"I feel helpless because the whole coast is threatened," she said. "What's the use of going all the way to Georgia if it can land there?"

Tiffany Miranda of Miami Springs waited well over 30 minutes in line at BJ's Wholesale Club in Hialeah to buy hurricane supplies. Some 50 vehicles were bumper-to-bumper, waiting to fill up at the store's 12 gas pumps.

Residents gather at the William Rivera Vocational School converted into a temporary shelter, before the arrival of Tropical Storm Dorian, in Canovanas, Puerto Rico, Wednesday, Aug. 28, 2019. Dorian became a Category 1 hurricane on Wednesday as it struck the U.S. Virgin Islands, with forecasters saying it could grow to Category 3 status as it nears the U.S. mainland as early as the weekend. (AP Photo/Carlos Giusti)

"You never know with these hurricanes. It could be good, it could be bad. You just have to be prepared," she said.

As of late Thursday morning, Dorian was centered about 220 miles (355 kilometers) northwest of San Juan, Puerto Rico, its winds blowing at 85 mph (140 kph) as it moved northwest at 13 mph (20 kph).

The National Hurricane Center's projected track had the storm blowing ashore midway along the Florida peninsula, southeast of Orlando and well north of Miami. But because of the difficulty of predicting its course this far ahead, the "cone of uncertainty" covered nearly the entire state.

Forecasters said it could bring 4 to 8 inches of rain to the Southeastern coast, with a foot possible in places, and trigger life-threatening flash floods.

Citizens stock up on supplies a few hours before the passing of tropical storm Dorian, in Canovanas, Puerto Rico, Wednesday, Aug. 28, 2019. Puerto Rico is facing its first major test of emergency preparedness since the 2017 devastation of Hurricane Maria as Tropical Storm Dorian nears the U.S. territory at near-hurricane force. (AP Photo/Carlos Giusti)

Also imperiled were the Bahamas, with Dorian's projected track running just to the north of Great Abaco and Grand Bahama islands.

The storm is expected to pick up steam as it pushes out into warm waters with favorable winds, the University of Miami's McNoldy said, adding: "Starting tomorrow, it really has no obstacles left in its way."

Gov. Ron DeSantis declared a state of emergency, clearing the way to bring in more fuel and call out the National Guard if necessary, and local governments distributed sandbags. Some residents used community Facebook groups to share updates on grocery stores getting new shipments of water.

At the Kennedy Space Center at Cape Canaveral, NASA decided to move indoors the mobile launch platform for its new mega rocket under development. A Rolling Stones concert Saturday at the Hard Rock Stadium near Miami was moved up to Friday night.

  • A girl walks on a sandy beach holding a sunflower and her flip flops after the passing of Tropical Storm Dorian, in the Condado district of San Juan, Puerto Rico, Wednesday, Aug. 28, 2019. The Hurricane Center said the storm could grow into a dangerous Category 3 storm as it pushes northwest in the general direction of Florida. (AP Photo/Ramon Espinosa)

  • Puerto Rico Gov. Wanda Vazquez speaks during a press conference in San Juan, Puerto Rico, Wednesday, Aug. 28, 2019. Forecasters said Dorian became a hurricane as it neared the U.S. Virgin Islands. The Hurricane Center says tropical storm conditions were expected Wednesday in Puerto Rico. (AP Photo/Gianfranco Gaglione)

  • A woman poses for a photo backdropped by ocean waters and a Puerto Rican national flag, after the passing of Tropical Storm Dorian, in the Condado district of San Juan, Puerto Rico, Wednesday, Aug. 28, 2019. The Hurricane Center said the storm could grow into a dangerous Category 3 storm as it pushes northwest in the general direction of Florida. (AP Photo/Ramon Espinosa)

  • Citizens stock up on gasoline a few hours before the passing of tropical storm Dorian, in Canovanas, Puerto Rico, Wednesday, Aug. 28, 2019. Puerto Rico is facing its first major test of emergency preparedness since the 2017 devastation of Hurricane Maria as Tropical Storm Dorian nears the U.S. territory at near-hurricane force. (AP Photo/Carlos Giusti)

  • Emergency Center personnel stand next to a tv screen showing a meteorological image of the tropical storm Dorian, as they await its arrival, in Ceiba, Puerto Rico, Wednesday, Aug. 28, 2019. Puerto Rico is facing its first major test of emergency preparedness since the 2017 devastation of Hurricane Maria as Tropical Storm Dorian nears the U.S. territory at near-hurricane force. (AP Photo/Ramon Espinosa)

  • People arrive to a private harbor to move boats away for protection ahead of the arrival of Tropical Storm Dorian in Boqueron, Puerto Rico, Tuesday, Aug. 27, 2019. (AP Photo/Ramon Espinosa)

  • Residents arrive at the William Rivera Vocational School converted into a temporary shelter, before the arrival of Tropical Storm Dorian, in Canovanas, Puerto Rico, Wednesday, Aug. 28, 2019. Dorian became a Category 1 hurricane on Wednesday as it struck the U.S. Virgin Islands, with forecasters saying it could grow to Category 3 status as it nears the U.S. mainland as early as the weekend. (AP Photo/Carlos Giusti)

The hurricane season typically peaks between mid-August and late October. One of the most powerful storms ever to hit the U.S. was on Labor Day 1935. The unnamed Category 5 hurricane crashed ashore along Florida's Gulf Coast on Sept. 2. It was blamed for over 400 deaths.

Dorian blew through the Virgin Islands and Puerto Rico as a Category 1 hurricane on Wednesday.

Puerto Rico seemed to be spared any heavy wind and rain, a huge relief on an island where blue tarps still cover some 30,000 homes nearly two years after Hurricane Maria. The island's 3.2 million inhabitants also depend on an unstable power grid that remains prone to outages since it was destroyed by Maria.

Several hundred customers were without power across Puerto Rico, said Ángel Figueroa, president of a utility workers union. Police said an 80-year-old man in the town of Bayamón died after he fell trying to climb to his roof to clear it of debris ahead of the storm.

Mency Serrano, 70, rests on a cot at the William Rivera Vocational School converted into a temporary shelter, before the arrival of Tropical Storm Dorian, in Canovanas, Puerto Rico, Wednesday, Aug. 28, 2019. Dorian became a Category 1 hurricane on Wednesday as it struck the U.S. Virgin Islands, with forecasters saying it could grow to Category 3 status as it nears the U.S. mainland as early as the weekend. (AP Photo/Carlos Giusti)

Dorian caused an island-wide blackout in St. Thomas and St. John in the U.S. Virgin Islands and scattered outages in St. Croix, government spokesman Richard Motta said.

No serious damage was reported in the British Virgin Islands, where Gov. Augustus Jaspert said crews were already clearing roads and inspecting infrastructure by late Wednesday afternoon.