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STORY: :: NASA TV

Hurricane Milton is barreling towards Florida's Gulf Coast.

:: The City of Treasure Island, Florida

Directly in its current path: the Tampa Bay metropolitan area, home to 3.1 million people.

Many of the area's residents have one final day to either evacuate, or hunker down and ride it out.

But what's at risk when this "catastrophic" storm hits?

:: What's the timeline?

:: CSU/CIRA & NOAA

The Tampa Bay area of Florida is facing a major hurricane for the first time in over a century.

:: Lt. Cmdr. Joshua Rannenberg, NOAA Corps.

Milton is forecast to hit the west coast of Florida late Wednesday or early Thursday and maintain hurricane strength when it reaches the Atlantic.

:: What damage is expected?

:: File

Hurricane winds push seawater called a storm surge, onto land. Milton is forecast to deliver a deadly storm surge of 10 feet (3 meters) or more of flooding to much of Florida's Gulf Coast.

While wind speeds could drop and downgrade Milton to a lesser category, the size of the storm was growing on Wednesday.

That puts more coastal areas in danger.

Winds, carrying trees and debris, could damage standing homes and destroy mobile homes, and cause power and communication outages.

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:: Cancun, Mexico

And then there's the rain: Some areas of central Florida will get up to 18 inches of precipitation.

According to the National Hurricane Center, Milton brings a "high risk of life-threatening flash and urban flooding" in metro areas of Tampa, Orlando and Daytona Beach.

:: What makes Tampa more vulnerable?

Tampa Bay, like the rest of Florida's Gulf of Mexico coastline, is vulnerable to storm surge.

:: Margaritaville Beach Resort Fort Myers Beach

Its shallow, gently sloping ocean floor retains water pushed toward land by wind, forcing the sea ashore.

Barrier islands near Clearwater and St. Petersburg are at particular risk.

Officials are urging island residents to head for the mainland to avoid drowning.

:: What precautions are underway?

Evacuation orders have been given in low-lying areas and other vulnerable communities in six counties around Tampa Bay.

Not all residents face mandatory evacuation.

But around 1 million people in coastal areas do.

Energy companies have also begun shutting down their pipelines and fuel-delivery terminals ahead of Milton's expected landfall.

:: Has Tampa had to deal with storms like this before?

The city of Tampa isn't used to storms on quite this scale.

The National Weather Service says the area was last hit by a major hurricane in 1921.

Eight people died, winds up to 120 mph were recorded, and a storm surge as high as 11 feet destroyed coastal structures.

Since then, its population has grown nearly sevenfold.

The unnamed hurricane in 1921 was a category 3.

Milton is expected to be a Category 5.