The U.S. National Hurricane Center said Saturday that Dorian was "expected to remain a powerful hurricane during the next few days" as the powerful Category 4 storm continued to approach the Bahamas.
The center said "some fluctuations in intensity are possible" and a "life-threatening" storm surge could raise water levels 3 to 5 meters above normal tide levels in northwestern Bahamas, where a hurricane warning was in effect. The surge will be accompanied by "large and destructive waves" near the coast, it said.
Forecasters said swells in the east-facing shores of the Bahamas, the east coast of the U.S. state of Florida and the southeastern U.S. coast were likely to cause "life-threatening surf and rip current conditions."
As of Saturday afternoon, Dorian was about 325 kilometers (200 miles) east of Great Abaco in the Bahamas and 625 kilometers (388 miles) east of West Palm Beach, Florida.
The storm was moving toward the Bahamas and Florida at 13 kph (8 mph). "The core of Dorian should move over the Atlantic well north of the southeastern and central Bahamas today, be near or over the northwestern Bahamas on Sunday, and be near the Florida east coast late Monday through Tuesday," the center said.
U.S. President Donald Trump has declared a state of emergency for Florida.
The center said because Dorian was moving slowly, it could produce prolonged rains, winds and storm surges, leading to life-threatening flash floods.
Dorian's maximum sustained winds increased from 220 to 240 kph (137 to 149 mph) Saturday.
Category 4 storms are capable of what experts describe as catastrophic damage.
Bahamian government officials urged hundreds of residents to evacuate their homes on low-lying cays in the northwestern Bahamas. Shelters were opened Saturday to accommodate evacuees.
The emergency declaration for Florida paved the way for the deployment of National Guard troops and the provision for more fuel for motorists.
Florida National Guard Major General James Eifert said 2,000 troops mobilized in the state Friday, with another 2,000 joining them Saturday.
Officials in Florida had not yet ordered any mass evacuations because the track of the storm was unclear.
Florida Governor Ron DeSantis has urged residents to stock up on at least a week's worth of food, water and medicine and be prepared to be without power for days after Hurricane Dorian makes landfall.