Tuesday, August 08, 2017

Tropical Storm Franklin: August 8, Update A

Today is Franklin’s Day. The Atlantic Blobette isn’t doing much, but Franklin has been to the buffet table quite a lot since yesterday, so he’s definitely the one to look at today.

Tropical Storm Franklin is currently at 19.1N, 87.3W, heading WNW at 14mph. His minimum pressure is 995mb with winds at 60mph, which makes him a mid-to-strong Tropical Storm (TS range: 39-73mph).

First, the track. The NHC were er… on track <grin> with their track forecast – again showing that they have that part sorted out to at least one day in advance. Hurray!! And there was much rejoicing. :-) That’s one big step for forecasting and one small step towards my retirement from this blog! Don’t worry, we have a couple more big steps to go before I can step back and hand things over to our benevolent robot overlords. ;-) 

The track from the NHC takes him over the Yucatan peninsula (he’s about to make landfall) and that seems right:

Second, the intensity. They currently have him as a mid-to-strong TS, but in my opinion he was a very weak hurricane - although as he interacts with land, he may be weakening already). You can see the signal of a well-formed storm in the vorticity maps (circulation). Here are the maps from the 850mb level (the lowest level of the troposphere), the 500mb level (mid-troposphere) – these you have seen in the past. But I have also added the 200mb level – the upper troposphere:

In addition to the fully formed Tropical Storm signal in the lower and mid troposphere (that deep red , even a little white, indicates a strong circulation), you can also see a signal in the 200mb level, which means his circulation extends from the bottom to the top of the troposphere – this means that his circulation extends from ground level to around 10-12 km above the surface of our planet! That is a lot of circulation in a storm, and something we see with hurricanes. The upper level is slightly off-set from the mid and lower level circulation, which indicates some light wind shear, but that is actually diminished from yesterday. 

If we look at the infrared satellite images, you can see that he is a pretty large storm in extent – with some of the outer bands extending over 1000 miles (you can estimate this because each degree in longitude is approximately 60-70 miles).  It does look like his convection is beginning to weaken as he moves away from the very hot sea surface waters and from interaction with land:

The NHC think he will remain a storm as he crosses the Yucatan and moves into the Bay of Campeche, even getting up to hurricane strength once he is there. A storm that takes a day to cross the Florida peninsula generally goes down by at least one and possibly to two categories, so I am not sure that he would still be a storm as he goes over the Yucatan, and if he is, he will be very very weak, which means the possibility of him regenerating into a hurricane is smaller. The thing to watch though is not his convection... it's his circulation (of course! you could have guessed that :-)). If he keeps his circulation pattern at 200mb, that means he has the physical structure to be a hurricane and all he needs is some yummy warm water to eat. That’s the key and the thing to look for as he crosses land.

I will try and post tomorrow, but the next two days look a little tricky (yes, I will be too busy eating ice cream, and cheese and wine … ;-))!

If you are in the Yucatan - stay safe!! 

I’ll be back when I can.

(p.s. any chocolate martini fans out there? If there is no ice-cream on the dessert menu, I have found an alternate. :-))

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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