Isaias rapidly intensifies into season’s first Atlantic hurricane as Gulf Coast braces for landfall

(CNN) — Isaias has rapidly intensified into the Atlantic season’s first hurricane, putting the northern Gulf Coast on alert for dangerous storm surge, damaging winds and flooding rain ahead of an expected landfall late Friday or early Saturday.

Hurricane hunter aircraft confirmed late Wednesday that Isaias had reached sustained winds of 75 mph, making it a Category 1 hurricane. The storm is about 450 miles south-southwest of the mouth of the Mississippi River and is expected to jog east-northeast for another day before turning sharply toward the northern Gulf Coast, strengthening further.

Rapid intensification is when a storm’s sustained winds increase by at least 35 mph in 24 hours or less, a feat more hurricanes are pulling off as Earth and its oceans warm from fossil fuel pollution.

Isaias could peak as a Category 2 with 110 mph winds by early Friday. It will weaken a little before making landfall as a dangerous hurricane by Friday night or early Saturday morning.

The storm’s forecast track has narrowed to a landfall somewhere from the Mississippi coast to the western Florida Panhandle, but how strong it will be when it arrives is still not set in stone.

A hurricane warning is now in effect from Ocean Springs, Mississippi, to Florida’s Bay-Gulf county line, including the Alabama coast. Somewhere within this area can expect winds of 74 mph or greater within the next 36 hours. A storm surge warning stretches from the mouth of the Mississippi River to Florida’s Steinhatchee River.

Flooding rain, powerful winds and storm surge will arrive at the coast beginning Friday, and those impacts could stretch well outside the forecast path shown above, especially to the east.

Florida Gov. Ron DeSantis declared a state of emergency for 25 counties Tuesday, urging residents to prepare disaster plans and stock hurricane supply kits. State emergency teams are staging generators, fuel, food, water and flood barriers in the Tallahassee and Santa Rosa areas to support the response.

Mandatory evacuation orders have been issued in two counties in the Florida panhandle. That includes residents in Okaloosa County’s coastal areas starting at noon Thursday, and officials urged all out-of-town visitors to leave by Wednesday evening. Nearby Gulf County issued a mandatory evacuation order for RVs at three parks and campgrounds due to potential flooding.

In neighboring Alabama, Gov. Kay Ivey on Wednesday announced a state of emergency for 40 counties in preparation for possible storm impacts.

Dauphin Island, on Alabama’s Gulf Coast, has issued a voluntary evacuation order starting Thursday evening for approximately 350 to 400 homes, city Public Safety Supervisor Troy Gorlott told CNN. The recommended evacuations include primarily low beach areas in the west end of the island that are made up of vacation homes and rentals, Gorlott said.

People in coastal and low-lying areas in neighboring Baldwin County are also “encouraged to begin preparing and relocate if needed,” the county’s emergency management agency said.

Oil companies are also taking precautions in the Gulf. Shell is evacuating nonessential personnel from six offshore platforms, while BP is removing nonessential workers and securing its offshore facilities, the companies said Tuesday.

Forecast timing and threats

Isaias should become increasingly lopsided when it arrives on the northern Gulf Coast. That means its worst wind, heavy rain, storm surge and tornado threats will be along and to the east of where its center tracks.

Rain, breezy winds and coastal flooding will start to ramp up as soon as Friday morning at the coast. Those conditions will worsen through the day and into the evening. Peak impacts will arrive when it makes landfall and last into Saturday morning.

Here’s what we know about the storm’s threats right now:

Flooding rain

Three to 6 inches of rain is expected, with localized totals up to 10 inches, from far southeast Louisiana to the Florida Panhandle. Up to 5 inches of rain could fall in other parts of the Southeast as far north and east as the Carolinas and the Tennessee Valley through Saturday.

The storm will move quickly, which will help keep flooding from being too widespread, but significant impacts are possible in limited areas. Isaias’ heaviest rain will lash southern Alabama and the western Florida Panhandle, upping the flash flood threat there.

Storm surge

Powerful winds from Isaias will build up Gulf water and propel it toward the coast, pushing it onshore in what’s called storm surge.

Coastal flooding could start as soon as Friday morning, but the biggest push of dangerous and life-threatening storm surge will be near and just east of where the storm’s center makes landfall on Friday night.

Locations on the coast from eastern Mississippi to Alabama, including Mobile Bay and the western Florida Panhandle, could see 5 to 7 feet of inundation above normally dry ground if the peak surge happens at high tide. This could flood roads and damage structures near the coast.

Wind

Isaias will grow larger as it nears the coast, which means windy conditions could be felt across a wide area of the South, especially Friday night through Saturday.

Tropical storm-force winds — 39 mph or greater — could arrive on the coast by midday Friday. Hurricane conditions are expected near and just inland from where the center makes landfall by late Friday.

The wind could down trees and knock out power both at the coast and over 100 miles inland in parts of the Florida Panhandle, Alabama and Mississippi.

Tornadoes

Isaias could produce at least a few twisters on its eastern side.

Tornado potential starts to ramp up on Friday night along the immediate coast. Tornadoes could spin up as far north as central Alabama on Saturday, although the risk area could shift or expand depending on the storm’s track.

Tropical tornadoes tend to be short-lived and sometimes pop up with little notice.

Conditions will improve over most of the South on Saturday night or Sunday as leftover rain from Isaias races toward the East Coast.

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CNN’s Maria Aguilar Prieto and Amanda Jackson contributed to this report.