Ryan Truchelut

WeatherTiger

It ain’t over till it’s over.

Yogi Berra said it. Lenny Kravitz said it. And now, I’m saying it.

Because as much as we’d all like it to be over, hurricane season is back again to dampen your weekend plans on the eastern Gulf Coast.

The key feature today is an area of showers and thunderstorms over the southwestern Gulf of Mexico, Invest 96L.

As of Wednesday afternoon, this convection is becoming more focused around broad low-level rotation northeast of Veracruz. Ocean temperatures remain in the mid-80s and mid-level moisture is ample, so despite marginal shear conditions, the development of a subtropical or tropical cyclone is likely by early Friday as the low moves slowly north-northeast.

Thursday morning update:Big Bend under tropical storm warning as Nestor expected to form in the Gulf

The next name on the list would be Nestor; the National Hurricane Center may also tag the low as a Potential Tropical Cyclone in order to issue coastal watches even if the system does not organize on Thursday.

Friday morning is when things get meteorologically weird, as the low accelerates northeast ahead of a shortwave trough pushing east across the northwestern Gulf.

Over the last two days, models are increasingly showing the mid-level rotation associated with the shortwave trough fully or partially merging with the mid-level rotation of the Gulf low. Exactly how this complex interaction, known as phasing, will play out is tough to predict.

Overall, the more the two features merge rather than clash, the more potential for a larger and somewhat stronger system to cross the northern Gulf Coast on Saturday.

If this doesn’t sound like the typical way that tropical storms intensify, it isn’t.

By closely interacting or phasing with a mid-latitude weather system, the Gulf low could have a hybrid or subtropical structure by Friday evening. That means the storm will be deriving its energy from not only the warm waters of the Gulf, but also the differences in temperature between the warmer eastern and cooler western halves of the system.

For this reason, hybrid or subtropical lows tend to lack the intense inner core of a purely tropical cyclone, have their strongest winds further from the center of the storm, and produce lower maximum winds for a given minimum pressure.

Nevertheless, this phaser could still stun.

The more the two systems merge on Friday, the farther east the low will probably track and the stronger it will be. As of Wednesday afternoon, the European model shows less phasing and a track towards eastern Louisiana, while the UKMET is fully phased, strongest, and furthest east, approaching Cape San Blas on Saturday morning. The GFS lies between the two in both projected track and intensity.

Model ensembles have been trending east as a clearer picture of the initial disturbance emerges, so I’d favor the center tracking more towards North Florida or Alabama than Louisiana at this early stage.

While there’s a lot of uncertainty regarding storm structure and motion, a wide area of gusty winds and heavy rainfall is increasingly likely between eastern Louisiana and central Florida between Friday afternoon and early Sunday, no matter the exact scenario that plays out.

Let’s be clear about what is not going to happen.

In no way, shape, or form is this system a potential Michael, Opal or even Hermine in the making for the Gulf Coast.

WeatherTiger on Michael:

Subtropical lows almost never reach hurricane intensity, and the system will likely encounter unfavorable westerly wind shear of 20-30 knots late Friday or early Saturday as it approaches the coastline. This is likely too much to allow even a hybrid system to do more than hang on as a mid-grade subtropical or tropical storm.

Some recent reference points for similarly unconventionally structured and sheared Gulf storms approaching North Florida from the southwest are Tropical Storm Josephine in 1996 and Tropical Storm Debby in 2012.

As with these systems, this Gulf low will be lopsided, with most heavy weather displaced north and east of its circulation center.

Rainfall will be the most significant impact, with widespread totals of 1.5 to 3 inches across the eastern Gulf Coast states and local totals to 5 inches or more certainly possible. With much of the Deep South in moderate to extreme drought, such rainfall would be outright beneficial across North Florida and Georgia.

The drawback to that rain is the potential for coastal flooding and tropical storm force winds along and east of the storm’s track.

While this is not going to be a widespread damaging wind event, a long southerly fetch of 20-40 knot winds pointed at North Florida would lead to a surge of at least several feet above normal tides, just as Tropical Storm Debby caused between three and four feet of surge in the Big Bend.

Water hazards aside, potential coastal wind gusts in the low-end tropical storm range would themselves present an outsized risk in Michael’s gash, where many residents are living in tents or badly damaged houses.

More:Hurricane Michael one year later: A collection of coverage as we revisit hard-hit towns

Overall, I’m hopeful that the positives from this late-season oddball system in terms of denting the ongoing drought will outweigh the negatives of coastal flooding; my biggest concern is that even relatively modest wind and surge will have a disproportionate impact on areas of the Florida coast that are not equipped to handle inclement weather.

Hurricane season is rounding the bases into its final 10%, but this week’s threat is just getting started. Keep watching the skies.

Dr. Ryan Truchelut is co-founder and chief meteorologist at WeatherTiger, a Tallahassee-based start-up providing advanced weather and climate analytics, consulting, and forecasting solutions to enterprises large and small. Get in touch at ryan@weathertiger.com or follow along on Twitter (@wx_tiger) or Facebook.