Tropical Storm Ian is gaining strength as it continues to churn through the northwestern Caribbean. It is set to slam western Cuba before turning north and aiming toward Florida later this week. A period of rapid intensification is expected to begin Sunday night and could continue through Tuesday as Ian enters the southeastern Gulf of Mexico.

The storm is projected to approach the coast of Florida as a hurricane late Thursday into early Friday, although its landfall location, strength and timing are still uncertain.

Florida is under a state of emergency, which Gov. Ron DeSantis expanded from two dozen counties to the entire state Saturday afternoon, highlighting the sense of danger and potential for destruction.

"The impacts will be broad throughout the state of Florida," DeSantis said during a briefing on Sunday morning. "Expect heavy rains, strong winds, flash flooding, storm surge and even isolated tornadoes," the governor added, saying that residents in the hardest-hit areas should brace for fuel disruptions, power outages and even evacuation orders. The Florida National Guard has also activated 2,500 Guard members, DeSantis said, adding that "if there's a need for more, then we can do more."

While the storm is most likely to hit Florida's west coast or Panhandle regions, the state's east coast could see flooding, DeSantis said, although he cautioned that models were still predicting a range of scenarios.

Computer models are divided on whether Ian will come ashore along Florida's west coast Wednesday into Thursday or nearer the Panhandle on Thursday into Friday.

Uncertainty "in the long-term track and intensity forecast is higher than usual," the National Hurricane Center wrote Sunday. "Regardless of Ian's exact track and intensity, there is a risk of dangerous storm surge, hurricane-force winds, and heavy rainfall along the west coast of Florida and the Florida Panhandle by the middle of the week."

Georgia Gov. Brian Kemp said his state will activate its emergency operations center Monday, and he encouraged residents to take precautions if the storm continues to intensify.

"Though models suggest it will weaken before making landfall on Thursday, and its ultimate route is still undetermined, Ian could result in severe weather damage for large parts of Georgia," Kemp's office said in a release Sunday.

Tropical storm conditions could reach South Florida as soon as early Wednesday and northern Florida by Thursday morning. Ian is predicted to peak as a 130-mph Category 4 hurricane west of the Florida Straits on Tuesday, which would make it the strongest September hurricane to pass through the Gulf of Mexico since Rita in 2005. But the storm's track and intensity are uncertain as it approaches the U.S. mainland. Tropical storm watches were issued Sunday for the lower Florida Keys.

President Joe Biden on Saturday approved an emergency declaration for the state, which authorized the Federal Emergency Management Agency to coordinate disaster-relief efforts and provided more federal funding. DeSantis said that he was "thankful" for the Biden administration's early response.

At 8 p.m. Sunday, Ian was centered 160 miles south of Grand Cayman, while churning to the northwest at 12 mph. Its peak winds were 60 mph, a 15 mph increase since Sunday afternoon. The storm will be moving over exceptionally warm waters, which are expected to fuel its intensification. Hurricane warnings are up in Grand Cayman and western Cuba as the storm progresses to the west and northwest. The greater Havana area is under a tropical storm warning.

The storm is expected to become a hurricane by Monday and reach "major" hurricane strength by Tuesday as it approaches western Cuba, according to the National Hurricane Center. Major hurricanes are Category 3 or above storms, packing sustained winds above 111 mph.