NEW YORK (PIX11) — Hurricane Ian was upgraded to an extremely dangerous Category 4 storm as it churned toward the Florida coast early Wednesday, one day after blowing through Cuba.

Roaring winds topped out around 155 mph early Wednesday, just shy of the mark needed to qualify as a Category 5 storm. Starting Wednesday, Florida’s west coast could feel the effects of those catastrophic winds, as well as devastating flooding.

Airports in Tampa, St. Petersburg, and Key West have already shut down ahead of the storm, as have Disney World and Sea World.

About two and a half million people have been advised to evacuate the area, and nearly 100 shelters have been opened, with more expected to open their doors Wednesday.

Some hospitals and nursing homes in the Tampa area, meanwhile, are moving patients.

In anticipation of the storm, many Floridians spent hours boarding up and sandbagging their homes and businesses on Tuesday.

Officials say the majority of buildings in Florida can sustain hurricane-force winds, but flooding is the serious issue.

Officials have also warned residents to prepare for a stretch of days without electricity.

“It is a big storm, it is going to kick up a lot of water as it comes in and you’re going to end up with really significant storm surge,” said Florida Gov. Ron DeSantis. “You’re going to end up with really significant flood events. And this is the type of storm surge that is life-threatening.”

It’s still unclear exactly where Ian will make landfall, and though the major hit is expected to the state’s west coast, it is also possible flash flooding could take place across the entire state.

Georgia and South Carolina could also see some flooding later this week.

This story also includes reporting from the Associated Press.