Dorian expected to strengthen into a Category 4 hurricane as it moves towards the US mainland.

Florida’s governor on Thursday extended a state of emergency to the entire state before the arrival of Hurricane Dorian, which is forecast to strengthen into a highly dangerous Category 4 storm during the weekend before hitting the Atlantic coast.

Governor Ron DeSantis took the step as authorities cancelled some commercial flights, planned precautions at rocket launch sites along the Space Coast and prepared to give out sand to residents for sandbags in advance of the storm’s arrival.

Spurred on by warm late-summer waters, Dorian is predicted to pack winds reaching 130 mph (209 kph) in 72 hours, the Miami-based National Hurricane Center said on Thursday.

That would make it a Category 4 storm, the second-strongest on the Saffir-Simpson scale for measuring hurricane intensity.

The centre describes Category 4 storms as capable of causing “catastrophic damage” including severe damage to well-built homes. It said in such storms, “Most trees will be snapped or uprooted and power poles downed.”

Dorian is likely to make landfall on Florida’s eastern coast on Monday before lingering over central Florida on Tuesday but tropical storm-force winds from Dorian could begin in parts of Florida as early as Saturday evening, the hurricane centre said. The storm could affect big population centres, as well as major Florida tourist destinations.

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“All residents, especially those along the east coast, need to be prepared for possible impacts,” DeSantis said in a statement. “As it increases strength, this storm has the potential to severely damage homes, businesses and buildings, which is why all Floridians should remain vigilant. Do not wait until it is too late to make a plan.”

The governor had declared a state of emergency for 26 counties on the east coast but extended it on Thursday to the whole of Florida.

Currently a Category 1 hurricane, Dorian was headed towards the Bahamas on Thursday after sideswiping Caribbean islands without doing major damage. Dorian is expected to strengthen and slam the Bahamas and the southeastern United States with rain, strong winds and life-threatening surf over the next few days.

Dorian was packing maximum sustained winds of 85 miles an hour (137 km/h) on Thursday morning some 220 miles (355 km) north-northwest of San Juan, and about 370 miles (600 km) east of the Bahamas, the hurricane centre said.

US President Donald Trump urged Floridians to heed official warnings.

“Hurricane Dorian looks like it will be hitting Florida late Sunday night,” Trump wrote on Twitter. “Be prepared and please follow State and Federal instructions, it will be a very big Hurricane, perhaps one of the biggest!”

The president cancelled his scheduled trip to Poland due to the storm, saying, “Our highest priority is the safety and security of the American people in the path of the hurricane.” US Vice President Mike Pence will attend the World War II commemoration in Warsaw and meetings with Polish leaders instead.

Store shelves are empty of bottled water as residents buy supplies [Marcus Lim/AP]

Jim McKnight, city manager of Cocoa Beach on central Florida’s Atlantic coast, made sure construction sites were secured with possible dangers like scaffolding taken down to prevent flying objects.

“We’re worried. This is not looking good for us. We woke up a lot more scared than we went to bed last night, and the news is not getting any better,” said Angela Johnson, 39, bar manager at Coconuts On The Beach, a Cocoa Beach bar and restaurant on the town’s surfing beach.

Officials were making piles of sand available for Cocoa Beach residents to fill sandbags starting on Friday.

The biggest hurricane to have come ashore in the area in recent history was Jeanne in 2004, which made landfall around Port St Lucie as a Category 3 storm.

‘Extremely dangerous’

“Dorian is expected to become a major hurricane on Friday, and remain an extremely dangerous hurricane through the weekend,” the hurricane centre said, warning of an increasing likelihood of life-threatening storm surge along portions of Florida’s east coast late in the weekend.

Two flights from the Orlando International Airport to Puerto Rico were cancelled.

The Cape Canaveral space centre said it would close Saturday afternoon with a skeleton team of roughly 100 staff staying behind in the launch control room to monitor the storm and the site’s aerospace assets.

NASA’s Kennedy Space Center said it would move a 122-metre (400-foot) tall, $650-million mobile launcher structure used to assemble the agency’s rocket for future moon missions from a launchpad and into a building to shelter during Dorian’s likely impact.

Nearby towns were checking storm drains and back-up generators for waste-water plants, as well as setting up round-the-clock shifts for emergency personnel.

The University of Central Florida, one of the largest US universities by student population, said its main campus in Orlando will close on Friday afternoon.

The storm was forecast to approach on Saturday the northwest of the Bahamas, a popular tourist spot, the hurricane centre said. Officials of the nation’s northernmost island Grand Bahama urged residents on Wednesday evening to secure houses and businesses immediately.