Originally Published: 28 AUG 23 02:55 ET

Updated: 28 AUG 23 13:55 ET

By Mary Gilbert, Robert Shackelford, Nouran Salahieh and Joe Sutton, CNN

(CNN) — Tropical Storm Idalia is expected to strengthen into a hurricane Monday and bring life-threatening and potentially catastrophic storm surge, winds and flooding rainfall to Florida’s Gulf Coast starting Tuesday into Wednesday as a Category 3 storm.

Concerns are mounting around Idalia’s expected strength as it goes through rapid intensification, something it is forecast to do up until it makes landfall along Florida’s Big Bend – a natural, storm surge-prone divot along the coast stretching from Tampa to just south of Tallahassee. Up to 11 feet of storm surge was forecast there.

Mandatory and voluntary evacuations were issued for at least five counties along Florida’s Gulf Coast with less than 48 hours before the storm makes landfall, and Florida Gov. Ron DeSantis warned of many more to come.

“This is going to be a major impact,” DeSantis said during a Monday morning news conference, warning Floridians should expect Idalia to be a major hurricane – Category 3 or higher – at landfall.

Key points:

Rapid intensification is expected: Idalia is forecast to rapidly intensify from a Category 1 hurricane Monday night to a powerful Category 3 hurricane just 24 hours later as it tracks over exceptionally warm water in the Gulf of Mexico.

A small shift in the track could dramatically affect Tampa: If Idalia were to make landfall farther south than currently forecast, Tampa could be hit with stronger winds and a larger storm surge.

Impacts well outside the cone: Storm surge, wind and rain will affect much of Florida’s Gulf Coast. After the storm makes landfall, damaging winds and heavy rain will spread far inland into Florida, parts of Georgia and even the Carolinas.

The storm is about 50 miles off the western tip of Cuba, whipping up maximum sustained winds of 70 mph, the National Hurricane Center said in an 11 a.m. ET update.

Idalia could arrive as soon as Tuesday

Impacts from Idalia will be felt from the Florida Keys to portions of the state’s western coast as soon as Tuesday. Wind speeds will increase across the Florida Keys and the state’s southwestern coast as early as Tuesday morning. Gusty winds are likely across a large portion of Florida, including inland areas, by Tuesday night as Idalia’s outer bands lap inland.

Wind, rain and storm surge will only increase in scope and intensity across Florida until it makes landfall on Wednesday morning as a powerful hurricane along the state’s Gulf Coast.

A large swath of Florida is expected to experience impacts from Idalia, but the worst of what the storm has to offer will stretch from Tampa northward through the Big Bend region and into portions of the Panhandle.

Conditions will deteriorate rapidly in these areas overnight into Wednesday morning as landfall draws closer.

Idalia’s life-threatening storm surge ‘our biggest concern’

Life-threatening storm surge up to 11 feet is possible in Florida’s Big Bend which will only be worsened by waves driven by hurricane-force winds in excess of 100 mph.

Storm surge, which is when a storm blows the ocean onshore, is one of the deadliest aspects of a hurricane and the reason behind most storm evacuations.

“Storm surge is often the greatest threat to life and property from a hurricane,” the Florida Division of Emergency Management agency warned. “It happens quickly and can endanger you, your family & your home.”

During Hurricane Ian, 10 to 15 feet of storm surge wiped buildings off their foundations in Fort Myers Beach, Florida. From Idalia, 7 to 11 feet of surge was predicted from Idalia, something Michael Brennan, the National Hurricane Center’s director, called “our biggest concern.”

“These are areas you don’t want to be in if you’ve been asked to evacuate,” Brennan said.

Storm surge alerts stretched along much of Florida’s Gulf Coast from just south of Naples north along all the way to the Panhandle near Apalachicola, highlighting how widespread the risk is.

As the storm approaches, the Tampa Bay area is forecast to see a storm surge of 4 to 7 feet above normal tidal levels, numbers that could change depending on Idalia’s final track.

Evacuations ordered in Florida

Mandatory and voluntary evacuations were issued in multiple Florida counties Monday morning, which DeSantis warned would expand.

“There are going to be evacuation orders issued in all these Gulf Coast counties in the A and B zones (and) all the barrier islands places that are low-lying on the coast,” DeSantis said.

Mandatory evacuations were ordered Monday for Pasco, Manatee, Hernando, Taylor and Pinellas counties for low-lying coastal areas and vulnerable structures.

Evacuations weren’t issued in the Tampa area yet, but officials there warned a decision would be made “very soon.”

“If and when the Governor issues an evacuation order, that means your life is in danger, hear those warnings,” Tampa Police Chief Lee Bercaw warned.

Tampa International airport announced it would cease all commercial operations by 12:01 a.m. Tuesday. The airport announced it aimed to reopen Thursday morning, after taking stock of what damage the storm left behind.

Governor DeSantis expanded an emergency declaration to 46 of 67 Florida counties on Monday morning.

DeSantis mobilized 1,100 National Guardsmen with high-water vehicles and aircraft for rescue and recovery efforts. The Florida Highway Patrol also has 300 troopers ready to deploy.

Power companies will also start staging personnel on Monday, according to the governor.

“If you are in the path of the storm, you should expect power outages so please prepare for that,” the governor told residents.

Georgia was also preparing for Idalia’s arrival. Governor Brian Kemp activated the State Operations Center Monday.

“Thanks to our response partners on both the state and local levels, Georgia will be prepared for whatever Idalia will bring,” said Governor Brian Kemp. “Rest assured, though the system will likely weaken before crossing our border, we’re not taking anything for granted.”