(NEXSTAR) – Hurricane Ian was still growing in strength Monday as it continued its path toward the continental United States. At 11 a.m. Monday, the massive storm was churning northwest at 13 mph, according to the National Hurricane Center (NHC).

At that pace and on its current path, the hurricane is expected to make landfall on Florida’s west coast as early as Wednesday. “Rapid intensification” of the storm is expected in the next 24 to 36 hours, the NHC said mid-day Monday.

The effects of Ian could be felt before the storm makes landfall, with tropical-storm-force winds forecast to reach the tip of Florida by 8 a.m. Tuesday morning.

Before reaching Florida, the storm was expected to blow through western Cuba. Then, it’s expected to slow down over the Gulf of Mexico, becoming bigger and stronger, turning into a Category 4 hurricane. By the time Ian reaches the U.S., winds are forecast to reach top speeds of 140 mph.

It’s not just winds that are a concern – the NHC warned “life-threatening storm surge” was possible along Florida’s west coast, especially between Fort Myers and Tampa. A surge of up to 10 feet of ocean water and 10 inches of rain was predicted across the Tampa Bay area, with as much as 15 inches in isolated areas. That’s enough water to inundate coastal communities.

Heavy rain could also cause flash flooding starting in the Florida Keys and the southern part of the state Tuesday, then further north Wednesday and Thursday.

As of Monday, Tampa and St. Petersburg appeared to be among the most likely targets for their first direct hit by a major hurricane since 1921.

“Please treat this storm seriously. It’s the real deal. This is not a drill,” Hillsborough County Emergency Management Director Timothy Dudley said at a news conference on storm preparations in Tampa.

After Thursday, the hurricane’s path is less clear. After hitting Florida, Ian is expected to weaken to a tropical storm and move toward eastern Alabama, Georgia and South Carolina. At some point Friday or Saturday, it could weaken to a tropical depression, though it’s too far out for forecasters to predict that exact timing.

The Associated Press contributed to this report.