MIAMI - Tropical Storm Isaias strengthened rapidly Wednesday afternoon, with NOAA Hurricane Hunters confirming 65 mph sustained winds by evening as the storm tracked toward the northern Gulf Coast, prompting hurricane and storm surge watches stretching from Louisiana to Florida’s Big Bend region, including portions of the Florida Panhandle.

The National Hurricane Center in Miami issued a Hurricane Watch from Bay St. Louis to Indian Pass, Florida, and a Storm Surge Watch from the Mouth of the Mississippi River to Yankeetown, Florida - a stretch of coastline that includes some of the Gulf’s most flood-vulnerable communities. A Tropical Storm Watch is in effect from the Jefferson/Plaquemines Parish line west of Bay St. Louis and from east of Indian Pass to the Aucilla River.

At 1 p.m. CDT Wednesday, Isaias was centered near latitude 22.6 North, longitude 93.4 West - about 255 miles west-northwest of Progreso, Mexico, and approximately 520 miles south-southwest of the mouth of the Mississippi River - with maximum sustained winds of 50 mph and a minimum central pressure of 997 mb (29.44 inches). By 7 p.m. CDT, Air Force Hurricane Hunters investigating the storm found winds had jumped to 65 mph and central pressure had dropped to 994 mb (29.36 inches), a notable intensification over just six hours.

The NHC forecast calls for Isaias to become a hurricane on Thursday as it passes north of the Yucatan Peninsula, then approach the U.S. northern Gulf Coast on Friday. The storm was moving east-northeast at 8 mph Wednesday evening. Forecasters expect a turn toward the northeast and north Thursday and Friday.

Tropical-storm-force winds extend outward up to 45 miles from the center. Hurricane conditions could begin in the Hurricane Watch area late Friday, with tropical storm conditions possible in watch areas by midday Friday, the NHC said.

The storm surge threat is the most immediate danger for Florida’s Gulf Coast. The NHC projects water could reach 5 to 7 feet above ground from Ocean Springs, Mississippi, to Indian Pass, Florida, and within Mobile Bay - life-threatening inundation if the peak surge coincides with high tide. From Indian Pass to the Aucilla River, surge heights of 3 to 5 feet are forecast. From the Aucilla River south to Yankeetown - a stretch that includes Levy and Citrus counties - surge of 2 to 4 feet is possible. Lake Pontchartrain could see 1 to 3 feet.

“The deepest water will occur along the immediate coast near and to the east of the landfall location, where the surge will be accompanied by large and dangerous waves,” the NHC advisory stated. “Surge-related flooding depends on the relative timing of the surge and the tidal cycle, and can vary greatly over short distances.”

Rainfall will compound the surge threat across the Florida Panhandle and surrounding region. From Friday through the weekend, Isaias is expected to drop 3 to 6 inches of rain across the central Gulf Coast from far southeastern Louisiana to the Florida Panhandle, with isolated totals up to 10 inches possible. Rainfall of 1 to 3 inches, with localized amounts up to 5 inches, is forecast across much of the Southeast as far north as the Tennessee Valley and the Carolinas. Flash flooding, urban flooding, and isolated river flooding are all possible.

Along the Yucatan Peninsula, coastal areas of the Bay of Campeche can expect 2 to 4 inches of rainfall through Thursday, with isolated higher amounts in the Mexican states of Campeche and western Yucatan. Gusty winds are also possible across the Yucatan on Thursday as Isaias passes to the north.

Dangerous surf and rip current conditions are expected to develop along the western and northern Yucatan Peninsula beginning Thursday, spreading northward toward the Gulf Coast by late in the week. The NHC warned these swells are likely to cause life-threatening surf and rip current conditions along Gulf beaches.

The NHC noted that additional watches and warnings could be required for portions of the U.S. northern Gulf Coast. Forecaster Blake signed the 1 p.m. advisory. The next complete advisory was scheduled for 4 p.m. CDT Wednesday, with updates continuing as Air Force Hurricane Hunters gathered additional reconnaissance data on the strengthening storm.

Residents from the Florida Panhandle east to the Big Bend region, including communities near Indian Pass, Apalachicola, and Yankeetown, should monitor updates from their local National Weather Service forecast offices and complete any storm preparations before tropical storm conditions make outdoor work dangerous by midday Friday.