Isaias reaches 105 mph overnight, 260 miles south of the Mississippi mouth

Hurricane Isaias was a Category 2 storm at 10 pm Central time on Thursday, with maximum sustained winds of 105 mph, about 260 miles south of the mouth of the Mississippi River. The National Hurricane Center's Advisory Number 10 placed the centre near 25.4 north, 88.4 west, moving northeast at 14 mph. Nine hours earlier, the 1 pm advisory had the storm at 85 mph.

The jump matters for the northern Gulf Coast because the warning area is already set and the clock to landfall is short. The Hurricane Center said Isaias could briefly become a major hurricane early Friday, then weaken some, and still come ashore as a dangerous hurricane late Friday or early Saturday. On the forecast track, the centre approaches the warning area on Friday.

A hurricane warning covers the coast from Ocean Springs, Mississippi, to the Bay and Gulf county line in Florida. A tropical storm warning runs from the Jefferson and Plaquemines parish line in Louisiana to a point west of Ocean Springs. Storm surge warnings remain in effect from the mouth of the Mississippi River toward the Florida Big Bend, including the stretch to the Suwannee River that forecasters have kept under a surge warning through the day.

The wind field is still compact. Hurricane-force winds extend outward up to 25 miles from the centre. Tropical-storm-force winds extend outward up to 125 miles. A small core can intensify quickly over the warm Gulf, and it can also weaken quickly if shear increases. The Hurricane Center's earlier discussion, written at 4 am CDT on Thursday, said vertical wind shear was expected to rise to 40 to 50 knots in the final 12 to 24 hours before landfall, which would likely take some strength off the storm even as the wind field grew broader and more lopsided.

That combination is the practical risk for inland counties. A broader wind field and a faster forward speed after landfall mean gusts travel farther from the coast than the category number alone suggests. The same discussion said heavy rain would reach the central Gulf Coast and much of the Southeast from Friday into the weekend, with flash flooding, urban flooding, and isolated river flooding possible. Georgia had already put every county under a state of emergency on Thursday. Mississippi, Alabama, and the Florida Panhandle sit inside the wind and surge warnings.

The overnight position also fixes the distance. At 10 pm the centre was about 295 miles north-northeast of Progreso, Mexico, and 260 miles south of the Mississippi mouth. At 9 am UTC on Thursday the centre had been near 23.3 north, 91.2 west, with winds of 80 mph and a central pressure of 979 millibars, about 445 miles south-southwest of the river mouth. In roughly 18 hours the storm moved northeast, gained 25 mph of sustained wind, and closed a large part of the gap to the coast.

Residents inside the hurricane warning have a narrow window. Hurricane-force winds are expected over portions of the Florida Panhandle, southern Alabama, and southern Mississippi. The Hurricane Center told people in those areas to prepare for long power cuts. People in the surge warning were told to follow local evacuation orders. A life-threatening surge is forecast along part of the northern Gulf Coast.

The storm's name is already familiar on this coast. An earlier Isaias struck the Carolinas in 2020. This system is a different cyclone, designated AL092026, and it has spent its short life over the Gulf rather than the Atlantic seaboard. The number in the advisory, not the reused name, is what counties are planning against.

Friday's early advisories will show whether the brief climb toward major-hurricane strength happens. If shear arrives on the schedule the 4 am discussion described, the peak may be short. The warning line from Ocean Springs to the Florida county border does not depend on that peak. It is already in force, and the centre is 260 miles from the river mouth.