Bryan Norcross: Chances increasing that Gulf system will become tropical storm

Proving the rule that there is so much energy in the Gulf water that almost anything that spins can organize into at least a tropical depression, the expansive low-pressure system centered over the Gulf just west of Tampa Bay has developed into Tropical Depression Two.

There is not much wind, but the rain bands have enough organization to fit the definition of a depression. The pressure near the center of the system is slowly dropping.

WHAT IS A TROPICAL STORM?

The National Hurricane Center is forecasting the system to become Tropical Storm Bertha by tomorrow.

Tropical Storm Watches have been issued for the Florida Panhandle from south of Tallahassee to the Alabama line.

Dry air is still penetrating the circulation both from the north and the south, but the very warm Gulf should provide plenty of moisture, allowing the system to strengthen and Bertha to form.

WHAT IS A TROPICAL DEPRESSION?

Slightly hostile upper-level winds from the northeast or north are forecast to plague the system during its time over the Gulf, which should put an upper limit on its intensity. And those upper winds will also hold most of the heaviest rain offshore, though tropical downpours will certainly affect the coastal zones from the west coast of Florida to Louisiana, including sections within about 50 miles of the coast.

There is a high consensus in the computer forecast models that the center of the broad circulation will move into the northeastern Gulf well south of Tallahassee tomorrow. After that, the future track seems to depend on how organized the system is.

If it has tall thunderstorms, which seems likely, it will be pushed west in the general direction of the Louisiana coast. If it’s weaker, it’s more likely to continue to drift closer to the coast or inland, but fewer computer forecasts indicate that scenario.

---

 

The National Hurricane Center’s forecast cone follows that thinking. The farther offshore it stays, the better opportunity it will have to get a bit stronger. As of now, the NHC’s forecast is for a 60-mph tropical storm drifting west offshore of the central northern Gulf Coast.

Here you see the location of the center as forecast by the European model (ECMWF), the U.S. GFS, the Google AI model, and the European AI model (AIFS) on Wednesday.

This graphic shows atmospheric moisture in the Gulf on Wednesday.

(FOX Weather)

Notice that the dark green, where the tropical moisture is concentrated, is mostly offshore. This is the work of the upper-level winds blowing out of the north, pushing the moisture south.

Still, the biggest threat is heavy rain from a slow-moving system first over the west coast and peninsula of Florida, and then across the eastern half of the Gulf Coast and surrounding areas. 

TROPICAL DEPRESSION TWO FORMS IN THE GULF, WITH HEAVY DOWNPOURS EXPECTED IN THE SOUTHEAST

Here is the map showing the forecast rain based on current forecasts. But higher amounts are likely to fall where a rotating band traverses the same area for an extended period of time.

This graphic shows forecast rain totals based on current forecasts.

(FOX Weather)

Notice that the heavier rain bulges north over the eastern Panhandle around Tallahassee because the storm will only slowly make the turn to the left.

Because of the somewhat hostile upper winds and dry air, there’s no indication that, from a wind standpoint, it will get terribly strong. But a 60 mph storm is not nothing.

If those sustained winds occur near the coast, gusts will reach hurricane strength.

HOW TO WATCH FOX WEATHER

Whenever systems are drifting over the warm water of the Gulf, we pay attention, of course.

In the affected areas, plan to stay aware at least until the middle of next week.