Gulf TS Bertha Forming

I was wrong. A depression has formed in the Gulf, and will almost certainly become Tropical Storm Bertha by tomorrow. Yes, I said that was possible, but what I didn’t think would happen would be a westward track towards us. First, let’s look at what’s out there. This visible satellite image shows that a broad surface circulation has formed - it’s more apparent in animated imagery where you can see the smaller cumulus rotating. The center is roughly south of Apalachicola (the point east of Panama City) and west of Tampa. Surface pressures have dropped significantly from yesterday in the Eastern Gulf. So, even though the cloud structure does not look like a tropical storm and the peak winds are less than 30 mph, this storm is forming.

The 10 AM National Hurricane Center shows their track and, given the lack of data in the Gulf, seems as reasonable as any. At face value, this places the storm in the marshes south of New Orleans Wednesday evening at tropical storm with gusts to 55 mph. But, this is far from certain since the storm is still forming and hasn’t been flown yet by a hurricane hunter. Models should do a much better job by late tonight after they fly the storm this afternoon to get critical data.

Tropical Storm watches are up along the Panhandle and Alabama beaches because if this deepens a bit faster than expected, it could give tropical storm force winds at the beach. Regardless, not exactly beach weather.

As I look at the ECMWF ensemble plots I’m somewhat encouraged. Below is a spaghetti plot NOT of various models, but of one of the best models run over and over again with slight “tweaks” to the initial conditions. It’s a way of trying to quantify uncertainty. The result shows a lot of variation, but there’s a few things that are worth noticing.

First, that there are more tracks south of the official NHC forecast than north of it. That’s good news. Second, the tracks over land feature higher pressures (look at the numbers next to the end of each line) and therefore weaker storms. So….if this tracks closer to the Slidell or Gulfport area, it would be a weaker system - a weak tropical storm. If it tracks towards the mouth of the river or even offshore paralleling the coast towards Texas, it could become a hurricane somewhere south of us. Either way, I have a hard time seeing St. Tammany, Hancock. or Harrison getting hurricane force winds out of this.

It’s certainly possible that we could get tropical storm force winds out of this and some storm surge into the Sound and Lake Pontchartrain. The timing looks to be Wednesday afternoon through early Thursday. Rainfall should be limited by dry mid level air ahead of the system and its steady movement to the west. This shows the ECMWF forecast of mid-level humidity (10-30 thousand feet) for Tuesday morning (courtesy of Tropical Tidbits). The brown shows a lot of dry air over us - this could limit the storms growth through Tuesday and it also means that our greatest chance of rain will be after it passes us.

So why the shift westward, this graphic (courtesy of “The Eyewall”) shows what the upper level winds will look like late Wednesday relative to the storm. An upper level ridge will be building into the north of us. That’s the reason for the westward turn. I’ll put out a more complete forecast later today or early tomorrow.