Tuesday, August 29, 2017

Tropical Storm Harvey and the Atlantic Blobette: August 28, Update A

First up tonight is The NeverEnding Story of…

Tropical Storm Horrible Harvey
He is really the storm that just won’t go away, isn’t he?

He is currently at 28N, 95W, heading ESE at 5mph. Officially his central pressure is 997mb, and winds are now 45mph, which still makes him a weak Tropical Storm (TS range: 39-73mph).

I would say he is a little stronger because the circulation is very strong in the lower half of the troposphere, and there is a small amount in the upper troposphere as well now. He is now back over water, to the southwest of Galveston bay… you can clearly see his center of circulation in the infrared satellite imagery because there isn’t as much convection near the center – it’s now a swirling mass of clouds. There is a lot of wind shear, which is why the convective clouds are streaming off to the northeast… in the direction of Houston/upper Texas coast, and Louisiana:
His forecast track takes him back onto land (another landfall!) at around 7am on Wednesday, along the Texas/Louisiana border.

Unfortunately, the flooding in Harvey is really extreme for at least three reasons: 

1. Rainfall is high and is continuing over the Houston area (the measurements range from around 21 inches to 36 inches so far). You can see the rain in the orange and yellow parts of the infrared satellite image as well as NOAA’s National Weather Service radar:

2. Now add to that, the controlled release of the dams in Houston is causing some additional flooding around those areas.

3. And the third piece to this puzzle is that normally the flood waters would stream out and into Galveston Bay and into the Gulf. However, the winds from Harvey are pushing water into the Bay, which we can see from the Tides Online data, where many of the tide gauges along the Bay are showing 2-4 feet of water above normal levels, and checking in with our favourite (with a ‘u’ ;-)), the Manchester station at the northern edge of the Bay...

… the waters here are now in excess of 11ft above normal! This will finally begin to change once Harvey moves past the Galveston area – which looks like it will be tomorrow evening. Then the winds will change and begin to blow the water off shore instead.

I got two queries today on how much rain will New Orleans expect… the official estimate is 5-15 inches. I don’t have a good way of predicting the amount of rainfall to expect unfortunately. If I find one, I will definitely share. But it looks like New Orleans have already had around 2-3 inches.

That’s it for Harvey for today, but there is still the…

Atlantic Blobette (formerly known as the Florida Blobette)
There is actually some change here today. First, this blobette looks like it is hanging out off the southern Carolina coastline (instead of Florida), which we can see in the circulation (vorticity) maps at the lowest level of the troposphere:
Second, the vorticity has improved in the middle of the troposphere, with what looks like a very faint signal in the upper troposphere (too soon to say if this will amount to much though) - middle and upper troposphere vorticity maps:

This suggests she is a Tropical Storm by now, but for some reason the NHC have her listed still as a "potential Tropical Cyclone", even though the wind speed is 40mph (TS range: 39-73mph). That is a bit odd! Perhaps everyone is tired from Horrible Harvey. 

Officially she is 32.5N, 79.5W, heading NNE at 7mph. Winds, as I mentioned, are 40mph, with a central pressure of 1006mb. The major convection and the circulation are fairly close to each other (separated by wind shear):

I really would say this is a Tropical Storm... North Carolina, did you get your wellies out?

That’s it for ce soir!  
Ciao for now!

Blogs archived at http://jyotikastorms.blogspot.com/
Twitter @JyovianStorm
DISCLAIMER: These remarks are just what I think/see regarding tropical storms - not the opinion of any organization I represent. If you are making an evacuation decision, please heed your local emergency management and the National Hurricane Center's official forecast and the National Weather Service announcements. This is not an official forecast. If I "run away, run away" (Monty Python), I'll let you know. 

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