Tropical Storm Isaias is forecast to become a hurricane before hitting the northern Gulf Coast late Friday or early Saturday

Isaias carried 65 mph winds and a central pressure of 994 millibars at 4 p.m. CDT on Wednesday, Oct. 7, and the National Hurricane Center expects the storm to reach hurricane strength by Thursday morning and come ashore on the northern Gulf Coast late Friday or early Saturday. Intermediate Advisory 5A, issued at 7 p.m., repeated that timetable without change.

A hurricane watch runs from Bay St. Louis, Mississippi, to Indian Pass, Florida, and a storm surge watch covers the coast from the mouth of the Mississippi River to Yankeetown, Florida.

Intensity Forecast: From 65 mph to a Category 2 Peak

The discussion that accompanied Advisory 5, written by NHC forecaster Blake, sets Isaias at 55 knots after Hurricane Hunter aircraft measured 700-millibar winds of 61 knots and the 994-millibar pressure. The official forecast reaches 70 knots, a hurricane, at the 12-hour point and peaks at 95 knots, or 110 mph, at 48 hours on Friday evening. Blake added that almost all guidance still shows a Category 1 or Category 2 hurricane at landfall. The Saffir-Simpson scale places Category 2 at 96 to 110 mph, so the forecast peak sits at the very top of that band and one mph short of the 111 mph threshold for a major hurricane.

Southwesterly shear is the brake. Radar shows the storm’s mid-level circulation sitting 5 to 10 nautical miles northeast of the low-level center, and the discussion expects shear to increase on Friday. The regional hurricane models also lowered their peak intensities in the latest cycle, and Blake wrote that it is “unknown whether this is the start of a real trend,” preferring to wait for more guidance before cutting the forecast. The hurricane-by-Thursday call is a forecast, and the discussion treats it as one.

The Track Between a Trough and an Atlantic Ridge

At Advisory 5 the center was about 225 miles west-northwest of Progreso, Mexico, moving east-northeast at 8 mph; by 5A the gap had closed to about 200 miles. The public advisory expects a turn north and then northeast on Thursday and Friday. Blake attributes the steering to a deepening trough and a strengthening ridge over the Atlantic, and the forecast was nudged slightly east toward the AI-based and corrected-consensus models.

The motion is slow for now, 7 knots in the discussion, which is why the timing is expressed as a window of roughly twelve hours rather than a single hour. Any change in forward speed shifts the arrival of tropical-storm-force winds, which the advisory places at midday Friday.

Landfall falls between the 48- and 60-hour forecast points, which translates to the stretch from Friday afternoon into early Saturday morning, matching the advisory’s “late Friday or early Saturday.” NHC’s Atlantic outlook listed no other system likely to form over the next seven days, leaving Isaias as the only Atlantic storm on the map.

Watch Areas From the Mississippi Delta to Yankeetown

Three watch types overlap. The tropical storm watch covers the Jefferson/Plaquemines Parish line to west of Bay St. Louis, plus the coast east of Indian Pass to the Aucilla River, flanking the hurricane watch on both sides. The NHC glossary says a hurricane watch is issued 48 hours before the expected onset of tropical-storm-force winds, and the advisory puts those winds in the watch areas by midday Friday and hurricane conditions late Friday. Surge heights, measured above ground if the peak coincides with high tide, step from 2 to 4 feet between the Steinhatchee River and Yankeetown up to 5 to 7 feet from Ocean Springs, Mississippi, to Indian Pass.

The National Weather Service office in Mobile said in its 6 p.m. Wednesday update that it expected the watches for coastal Alabama and the western Florida Panhandle to be upgraded to warnings overnight, and it flagged 20 to 25 foot breakers east of the center starting Friday.

Rain, Tornadoes and the Lopsided Side of the Storm

Wet ground compounds the rain forecast. The Mobile office’s update noted that the Alabama coast already took heavy rain and flooding last weekend, which leaves less room for the new totals to soak in before runoff turns into flash flooding. The advisory itself carries the flash flood and urban flooding caveat across the whole rain area, and the tropical-storm-force wind field extends up to 60 miles from the center, so the gusts and rain bands reach well beyond the coastline named in the watches.

Rainfall of 3 to 7 inches, with localized totals up to 10 inches, is forecast from far southeastern Louisiana to the Florida Panhandle from Friday through the weekend, and 1 to 3 inches, locally 5, across much of the Southeast up to the Tennessee Valley and the Carolinas. Tornado potential rises Friday evening and overnight as rain bands reach the northeastern Gulf Coast, then spreads inland on Saturday.

The National Weather Service in Tallahassee describes the impacts as lopsided, concentrated along and east of the center, and lists a high rip current risk for Walton, Bay, Gulf and Franklin counties through Monday. Blake’s discussion carries the storm inland at 60 knots on Saturday morning and has it post-tropical by Sunday.

This article was produced with the assistance of AI and reviewed by Morning Overview editors prior to publication.

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