Brewing Gulf Storm Takes Aim at Upper Texas and Louisiana Coasts

Hurricane and Storm Surge Watches expected for portions of the northwestern Gulf Coast today

Monday morning sunrise satellite of Potential Tropical Cyclone Six in the southwestern Gulf of Mexico

A large disturbance over the southwestern Gulf of Mexico is organizing and is expected to become Tropical Storm Francine later today as it sets its sights on the northwestern Gulf Coast.

The National Hurricane Center is forecasting the system to strengthen to a hurricane before reaching the Upper Texas and Louisiana coasts by late Wednesday or Thursday, and hurricane and storm surge watches will be issued for these areas in the coming hours.

Brewing storm takes shape

Last Thursday, we discussed the significance of fall fronts to tropical formation, especially when they fester long enough over warm waters. Like clockwork, the same front parked over the Gulf of Mexico last week became a catalyst over the weekend for our next named storm.

The system now designated Potential Tropical Cyclone Six – the NHC designation given to developing disturbances expected to threaten land – came about from a hodgepodge of weather features, including a low-pressure area (formerly Invest 90L) attached to a stalled front in the western Gulf and a long-tracked tropical wave (Invest 91L) that emerged over the lower reaches of the Gulf of Mexico, now siphoning off spin from the leftover frontal boundary.

Hurricane hunters investigating the area before daybreak Monday continued to find a broad and elliptically-shaped area of low pressure without a well-defined circulation. Winds around the developing storm, however, are already above tropical storm strength (39 mph or stronger), which means that whenever the circulation center becomes better defined – expected by Monday afternoon or evening – the system will be upgraded straight to Tropical Storm Francine.

A new hurricane hunter mission is currently underway.

Hurricane threat to the Upper Texas and Louisiana coasts by mid week

Until the circulation becomes better defined and thunderstorm activity becomes more focused directly over the center, only slow strengthening is expected. Although the steering pattern supports a movement toward the Upper Texas and Louisiana coasts, the absence of a coherent and well-defined circulation also means we can expect some variability in the details of exactly where and when the anticipated hurricane comes ashore.

Odds of the center of future Francine passing to within about 100 miles of a given location based on the overnight runs of our reliable global forecast models. The greatest odds of experiencing the direct impacts from the forecast hurricane are from the Upper Texas coast through much of coastal Louisiana. Credit: Tomer Burg/University of Oklahoma

That said, the environment ahead looks ripe for strengthening once a circulation pulls together and forecast models are advertising at least steady strengthening, with a 1 in 3 odds of rapid strengthening, tomorrow into Wednesday. For now, intensity guidance suggests a Category 1 hurricane near landfall on Wednesday or Thursday, and NHC is forecasting maximum winds of around 80 mph as future Francine comes ashore. We’ll need to monitor the intensity trends given the extremely warm waters and light upper-level winds, but models do show wind shear on the rise as it approaches the coast which could at least keep it in check.

A considerable flash and urban flood threat from double-digit rainfall totals will accompany the system across parts of southern Louisiana and southeastern Texas.

In addition, serious life-threatening storm surge can be expected near and to the east of where the center comes ashore. The looming storm is targeting an especially storm-surge-prone area of the northwestern Gulf Coast so coastal residents should listen for and heed any evacuation orders in the coming hours.

Possible Atlantic development but no threats to land

The National Hurricane Center is tagging two systems in the open Atlantic well east of the Caribbean for possible development this week.

Forecast models have been inconsistent in predicting which of these two systems will develop, if at all, in the week ahead. For now at least forecasts keep whatever comes of either over the open Atlantic and generally away from any land areas.