(CNN) — Floridians are bracing for Tropical Storm Ian, which is expected to rapidly intensify and become a hurricane on Monday before hitting western Cuba, bringing with it the threats of strong winds and storm surge as high as 9 to 14 feet, according to the National Hurricane Center.

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Ian’s exact path beyond Tuesday remains unclear: The storm, which developed Friday in the central Caribbean Sea, is expected to reach the US later this week, but with models showing a wide spread of possible scenarios, it’s too early to know where the storm will hit, when — and how strong it will be.

The storm began strengthening Sunday night, with sustained winds of winds of 60 mph, according to the National Hurricane Center. “Additional strengthening is forecast tonight, followed by more rapid strengthening on Monday and Tuesday,” the center said.

The first US tropical storm watches associated with Ian were issued Sunday and are in effect for the lower Florida Keys from Seven Mile Bridge to Key West and including the Dry Tortugas, the hurricane center said.

The storm is forecast to become a hurricane on Monday and then a major hurricane on Tuesday, meaning Category 3 or higher, the center said.

Meteorologists predict the storm will peak at Category 4 strength over the eastern Gulf of Mexico in three days, but Ian is then expected to weaken before reaching Florida.

Still, Florida officials are urging residents to be prepared for the worst, and the hurricane center warned Sunday morning of 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, regardless of the storm’s exact track and strength.

“We’re going to keep monitoring the track of this storm, but it’s really important to stress the degree of uncertainty that still exists,” Gov. Ron DeSantis said in a news conference Sunday, warning residents that even if the storm weakens before landfall, it would “still have significant impacts.”

Floridians can expect “heavy rains, strong winds, flash flooding, storm surge and even isolated tornadoes,” the governor said. But the director of Florida’s Division of Emergency Management was particularly focused on the storm surge threat, cautioning that whatever surge develops while Ian is a major hurricane could persist as it nears land, even if the storm weakens.

“We could see a situation where we have Cat 4 storm surge and potentially a Cat 1 or 2 hurricane landfall,” Director Kevin Guthrie said.

Anne Bink, associate administrator of the Federal Emergency Management Agency’s Office of Response and Recovery, kept the message simple: “Prepare now.”

Florida residents should know their evacuation routes and have preparedness kits that can last them at least three days, Bink told CNN. “Things like food, water, battery chargers for your phone. Even things like your insurance documents — take pictures of them so you have them with you,” Bink said.

“We expect rapid intensification with this storm,” Bink said. “My message is: Please take this seriously, and please listen to your local officials.”

In the meantime, Ian is expected to be a major hurricane by the time it passes near or over western Cuba, the hurricane center said Sunday morning, and forecasters are becoming more confident residents there will face life-threatening storm surge and hurricane force winds.

As of Sunday night, Ian was about 160 miles south of Grand Cayman and about 430 miles southeast of western Cuba.

A hurricane warning is in effect for Grand Cayman and several Cuban provinces, including Isla de Juventud, Pinar del Rio and Artemisa, while a tropical storm warning has been issued for the provinces of La Habana, Mayabeque and Matanzas.

The Cayman Islands government has issued tropical storm watches for Little Cayman and Cayman Brac, according to the hurricane center.

Tropical storm conditions are possible across Cuba on Monday afternoon, and hurricane conditions will likely follow late Monday into Tuesday, the hurricane center said. Ian is forecast to bring 6 to 10 inches of rain with isolated totals up to 16 inches possible in western Cuba. That could contribute to flash flooding or even mudslides in areas of high terrain. And storm surge is forecast along the coast of western Cuba from Monday night into Tuesday.

According to the hurricane center, Ian will keep its major hurricane status as it moves north through the Gulf of Mexico.

Florida readies for potential hurricane, flooding and winds

Authorities in Florida are distributing sandbags and asking Floridians to prepare their property to reduce the risk of storm damage and to stock up on supplies like radios, water, canned food and medication. Residents should also pack up important documents and know their evacuation routes.

“This is the calm before the storm,” Naples Mayor Teresa Heitmann told CNN on Saturday. “We experience this kind of adrenaline before a storm and the path could change at any time, but we want our citizens to be ready.”

DeSantis echoed that Sunday, telling reporters at his news conference, “It’s better to be prepared and not have to use those preparations.”

To that end, DeSantis on Saturday expanded an emergency order to include every county in the state, saying conditions are “projected to constitute a major disaster.” President Joe Biden declared an emergency for Florida and ordered federal assistance to supplement response efforts. On Sunday, DeSantis announced 2,500 National Guardsmen had been activated ahead of the storm.

St. Petersburg, southwest of Tampa, is in a vulnerable position as a “peninsula within a peninsula within a peninsula,” Mayor Kenneth Welch told CNN’s Fredricka Whitfield on Sunday.

Despite the storm’s unpredictable course, Welch said he’s encouraging residents to prepare emergency provisions for at least a week.

“As we’re watching the storm, certainly praying it continues to move west, we at the same time are asking folks to prepare, make sure they have a plan, know their evacuation zone, take care of those things like food and water for seven days,” Welch said.

Any evacuation orders will be given at least 72 hours in advance, the mayor said.

In Daytona Beach, Bethune-Cookman University issued a mandatory evacuation order and canceled classes Monday with plans to resume online Tuesday. Concerns over Ian’s arrival have also delayed the Artemis I rocket’s third launch attempt planned for Tuesday. And in Cape Coral, Mayor John Gunter said the city’s emergency operation center was operating at an “enhanced level.”

“Right now, of course, we are like many other cities,” Gunter said. “We’re preparing for the worst. Hoping for the best.”

Storm surge — when the force of a hurricane or storm pushes ocean water onshore — can be one of the greatest threats to life and property from a hurricane. This is the primary reason Miami-Dade County residents are asked to evacuate before a hurricane, according to county officials.

“We’re outside of the cone of uncertainty. We can’t relax,” Miami-Dade County Mayor Daniella Levine Cava told CNN on Saturday. “We know there’s always a possibility it will shift. The storm has continued to move westward. This is the time everyone should make sure they have a plan.”

Levine Cava urged residents to ensure they have enough food and water and check their storm surge planning zone.

“We’re very hopeful that even with a major rain event, we’ll be able to manage it,” she said. “We’re on standby. We have extra pumps, and we’ve worked with the South Florida Water Management District to lower canal levels.”

Miami-Dade County is preparing its “extensive shelter system,” including for those fleeing the Florida Keys if evacuations are ordered there.

Heitmann is already seeing lines at the gas stations in Naples as residents brace for the potential hurricane, she said.

“They’re taking it serious, and I encourage those that are not to always take a storm serious, because you can never estimate where that storm might turn. And we need to be prepared and if it’s not coming directly for us, it might have strong winds,” Heitmann said.

In Sarasota, authorities are checking on generators, planning with local police, trying to estimate how much flooding is possible and warning residents to be prepared, Mayor Erik Arroyo told CNN.

“Don’t underestimate the dangers that come with gusts, with storm surges, with flooding, especially us being a coastal city. So we’re telling them to go now, be prepared early,” Arroyo said.

In neighboring Georgia, Gov. Brian Kemp ordered the State Operations Center to prepare for any potential impact from the storm.

“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,” a Sunday news release from the governor’s office said.

“I urge my fellow Georgians to monitor this storm as it evolves and calmly take the necessary precautions to keep their families and neighbors safe, if the storm continues to intensify,” Kemp said.