Hurricane Ian updates: Florida death toll climbs

Tropical Storm Ian has weakened slightly, but it is expected to not only strengthen but rapidly intensify overnight as it travels over warm waters in the Caribbean.

As of 5 p.m. ET, the storm system had maximum sustained winds of 45 mph and was moving west-northwest at 12 mph, with the center located about 220 miles away from Grand Cayman.

Dry air ahead of the storm has delayed the strengthening trend so far. But the rapid intensification is expected to occur Monday into Tuesday as the system continues across the northwestern Caribbean and closes in on western Cuba.

Over the next 24 hours, the outer bands will impact Jamaica and the Cayman Islands, bringing rounds of heavy rain, possible flash flooding and storm surge. Later Monday and into Monday night, Ian will be closing in on western Cuba and will likely bring significant wind and storm surge impacts to the region.

A hurricane warning is in effect for Grand Cayman and portions of western Cuba. A tropical storm watch has been issued for portions of western Cuba, as well as the lower Florida Keys, including Key West.

As of 5 p.m., the forecast track was nudged slightly eastward. Overall, the forecast guidance variability and uncertainty will remain high, and the track for where the storm will be from the middle to the end of the week will continue to shift over the next 24 to 48 hours.

-ABC News' Dan Peck

Caribbean islands such as Jamaica and Grand Cayman will start to experience the effects from the outer bands of Tropical Storm Ian within the next 24 hours, forecasts show. The islands will experience conditions such as heavy rain, possible flash flooding and storm surge.

The storm system will begin to rapidly intensify overnight into Monday before it closes in on western Cuba on Monday night.

As of 2 p.m., the sustained winds in the tropical storm remained at 50 mph as it moved west-northwest at 12 mph, the center about 265 miles away from Grand Cayman.

Hurricane warnings are in effect for Grand Cayman and western Cuba, while tropical storm warnings and watches are in effect in other portions of both islands.

As a hurricane, Ian is expected to peak at a Category 4 before weakening slightly as it looks to make landfall on the west coast or panhandle of Florida in the coming days.

There is still some uncertainty to the track Ian will take once the system enters the Gulf of Mexico.

The center of the storm and the worst of the impacts could end up heading toward the western coast of Florida's peninsula, including the Tampa area. The other possible scenario has the storm moving more due north and bringing a possible landfall along the Florida peninsula, impacting cities like Panama City and Tallahassee with more direct effects.

The storm will begin to impact the Florida keys and the southern portions of the state by Tuesday night.

-ABC News' Dan Peck

Tropical Storm Ian is marching toward the Gulf Coast of the U.S., a region quite vulnerable to hurricanes.

The underwater geology of the Gulf of Mexico is what makes the Gulf Coast particularly unguarded to the massive influx of seawater, said Michael Brennan, acting deputy director of the National Hurricane Center, according to an article on Inside Science.

The symmetry of the Gulf of Mexico, with its shallow, sloping continental shelf, allows the storm surge to be pushed even higher onto land, Brennan told the outlet.

Because the land around the Gulf Coasts is typically flat, that exacerbates the flooding even more and allows the storm surge to travel farther inland, Brennan said.

"Of all of the hazards of hurricanes --- winds, rain, storm surges –-- surges are what can cause the largest loss of life," Brennan told Inside Science.

The Tampa Bay-St. Petersburg area, one of the regions bracing for Ian, is especially vulnerable to storm surge flooding but has avoided a direct hit from a strong hurricane since 1921.

Editor's Note: This post has been updated to reflect proper attribution to Inside Science.

-ABC News' Max Golembo

Florida Gov. Ron DeSantis is imploring Floridians to prepare for Tropical Storm Ian, no matter which side of the state they live on.

While Ian is forecast to make landfall on the west coast or panhandle of Florida in a matter of days, DeSantis warned those not in its direct path against a false sense of security.

"Just don't think that if you're not in that eye, that somehow you don't have to make preparations," DeSantis said during a news conference on Sunday. "The last thing we want to see you see it start to really bear east quickly and then have folks who are not prepared."

DeSantis, who has declared a state of emergency ahead of the storm, will be requesting assistance from FEMA, he said.

About 2,500 Florida Nationals Guardsman have been activated to respond to the storm.

-ABC News' Miles Cohen