Millions along the US east coast from Florida to North Carolina remained under threat of a deadly strike from Hurricane Dorian on Saturday, even as official predictions for the path of the 150mph monster storm pulled back from a direct hit on land.

Dorian was poised to tear through the northern islands of the Bahamas on Sunday after beefing up into a category 4 hurricane late on Friday. The storm was heading west towards the mainland US and what was initially expected to be the most powerful hit on Florida’s east coast in almost three decades on Tuesday.

But after a nervous week in which longer-range forecasts from the Miami-based National Hurricane Centre (NHC) enveloped almost the entire state of Florida in its “cone of uncertainty”, the expected track for the storm was recalibrated early on Saturday to a northerly crawl at sea towards Georgia and the Carolinas, steered by a weakening atmospheric ridge over the Atlantic.

“There is hope,” said Jeff Masters, director of meteorology at Weather Underground.

Even so, officials warned of significant and potentially devastating impacts, even if the centre of the storm remained offshore or just inland, as a dwindling number of models continued to suggest. They pointed to Hurricane Matthew in 2016, a category 5 storm that followed a near identical track to Dorian’s predicted path, hugging the coastline of Florida, Georgia and the Carolinas, causing hundreds of billions of dollars in wind and flood damages in the US, killed 47 and left millions without power.

Don’t make any assumptions. Remain vigilant and be prepared Governor Ron DeSantis

In an afternoon advisory, the NHC posted tropical storm warnings for portions of Florida’s east coast and warned that Dorian still had some strengthening to do, its winds expected to peak at 155mph, 2mph short of category 5 status, by the end of the day.

“Even if it doesn’t directly strike Florida, this is still a big, powerful storm,” Ron DeSantis, the Florida governor, said in a Saturday morning briefing. “You’re still looking at really significant storm surge on the east coast, you’re looking at major flooding events in different parts of the state, so the effects can range.

DeSantis said: “A bump in one direction or the other could have significant ramifications in terms of impact. If it bumps further east that obviously is positive [but] if it bumps just a little west then you’re looking at really, really significant impacts. Don’t make any assumptions. Remain vigilant and be prepared.”

Lixion Avila, a senior hurricane specialist at the NHC, echoed the warning later, predicting a “prolonged period of life-threatening storm surge, devastating hurricane-force winds and heavy rains capable of life-threatening flash floods” for the Abaco Islands and Grand Bahama, reaching the US next week.

“Since Dorian is expected to slow down and turn northward as it approaches the coast … storm surge and dangerous hurricane force winds are still possible along the Florida east coast. There is an increasing risk of strong winds and dangerous storm surge along the coasts of Georgia, South Carolina and North Carolina during the middle of next week.”

David Bibo, Federal Emergency Management Agency (Fema) deputy associate administrator for response and recovery, was more succinct, branding Dorian “a long duration nailbiter”.

Mandatory evacuation orders were issued but later postponed for 24 hours for barrier islands and coastal areas of Florida’s Brevard and Martin counties, including the Kennedy Space Center at Cape Canaveral, with voluntary requests for evacuation in several other counties.

DeSantis declared a state of emergency in all 67 counties before the weekend, and said he had spoken with Donald Trump on Friday night. The president, he said, had promised whatever federal support was needed but “hopefully that won’t be necessary”.

As the immediate threat to southern and central Florida appeared to lessen, Trump tweeted his fears for other parts of the US.

“Looking like our great South Carolina could get hit MUCH harder than first thought. Georgia and North Carolina also,” he wrote. “It’s moving around and very hard to predict, except that it is one of the biggest and strongest (and really wide) that we have seen in decades. Be safe!”

We’re more nimble and all his agencies are here Stephanie Grisham

Trump was at his Virginia golf club, having travelled there by helicopter from Camp David in Maryland.

On Friday, Trump had given the impression as he left the White House that he would spend Saturday at Camp David with experts, monitoring Dorian’s progress, and would return to Washington on Sunday to attend a briefing at Fema.

Stephanie Grisham, the White House press secretary, said Trump received updates every hour during his time at his club before his scheduled return to Camp David for a hurricane briefing.

“He has someone travelling with him to specifically brief him on an hourly basis,” she told a reporter for the White House press pool, adding that it was better for him to remain in the US after cancelling a planned weekend trip to Poland.

“We’re more nimble and all his agencies are here,” she said.

The governors of North Carolina and Georgia declared states of emergency on Thursday and Friday. Henry McMaster, the South Carolina governor, was expected to follow suit on Saturday.

Although expected to weaken slightly, Dorian was still expected to be menacing the coast of Georgia and the Carolinas by Wednesday or Thursday as a category 3 storm, still pushing out winds of up to 130mph.

In the Bahamas on Saturday, canned food and bottled water were disappearing from shelves and the sound of hammering echoed across the islands as people boarded up their homes. Dorian was expected to hit the north-western islands by Sunday.

“To those of you in the Cays and Grand Bahamas, I beg you, please leave,” the prime minister, Hubert Minnis, said.

“Dorian is expected to cause devastating effects to our island. If you wait until tonight, it will be too late. Time is not on our side.”

Associated Press contributed to this report