Sunday, August 15, 2021

Remnants of Fred and Tropical Storm Grace: 14 August, Update A

I have my wine, I have my bar of Cadbury's Fruit & Nut... living it up in style on a Saturday night. ;-) For those who got yesterday's Famous Fred, yes, it was Freddie Mercury and the lyrics casually thrown in were from Bohemian Rhapsody. But today, in addition to Fred we have Grace.

Remnants of Fred

I'm not surprised that he fell apart - the land and the wind shear took their toll. He is currently over water again in the Gulf of Mexico, but is looking rather wishy washy. The only reason we are still talking about him is because the NHC think he will re-develop as he crosses the Gulf. So... the pretend official center is around 23.8N. 84.3W, and he is supposedly heading WNW at 9mph. This is his estimated track... 

They haven't made much changes to his wind speed (still 35mph) or central pressure (still high for a storm at 1012mb), but they think he will be a Tropical Storm tomorrow according to the forecast above. I'm not convinced of this yet.

His convection is currently almost non-existent: 

That could change tomorrow of course. But the real clue is in his vertical structure and his vorticity (circulation), which no longer looks like a tropical system at any level. Here's the vorticity map at the lowest level of the troposphere (850mb): 

You can clearly see the difference between the signal for Fred, which is elongated and not a tropical storm, and the one for TS Grace (in the region of the Leeward Islands/Caribbean), which is circular. And here's the map at the mid-level of the troposphere (500mb):

At this level, Fred's vorticity is elongated in a completely different direction than his structure lower in the troposphere, meanwhile Grace continues to have a well-developed circular pattern stretching to these heights in the troposphere. 

And as a bonus, for comparison you can also see Hurricane Linda on these maps in the eastern Pacific - she's the very red/white hot circular blob to the left of the map in both levels of the troposphere. Hurricane Linda is a major cat 3 hurricane with winds of 125 mph, central pressure of 955mb. This is what strong circulation looks like. 

The question is will Fred re-form and if he does, where will he go and how strong will he be. Well, it's a bit up in the air, like this really...

(tee hee). (Yes, today's Famous Fred is Mr. Astaire)

The NHC don't really know where his center of circulation is because he is so weak but this blob-formerly-known-as-Fred will move generally northward because he is essentially skirting around an area of high pressure. 

There continues to be some wind shear at least in the eastern Gulf which won't help him much. Depending on his path, I think if he does re-develop, he won't amount to much at all - but because there is some vorticity and the Gulf of Mexico waters are warmer than 30 deg C, whether or not he is a storm, he will still bring some clouds/rain/squalls (he already is actually) and a bit-o-wind to Florida and the northern Gulf. I mention his path as being important because if he moves along the western edge of that Cone of Uncertainty, there is a chance that he will pass over the Loop Current - this is a region of very deep warm water and we have seen many storms intensify as they got over this sort of region in the ocean. At the moment, the Loop Current is due south of Mobile Bay - so it does intersect with the Cone but it doesn't look like he will go over it until Monday, so we will know tomorrow if that looks like a possibility. 

Tropical Storm Grace

Not surprisingly, Tropical Storm Grace was named very early this morning and is now at 16.8N, 62.4W, heading WNW at a very rapid 20mph. She is barely a TS with winds of 40mph, central pressure of 1010mb (TS range: 40-73mph) and recently crossed into the Caribbean near Guadeloupe. Her weak status is because she had to get through that dry SAL that I mentioned yesterday. 

Her forecast track takes her to Puerto Rico and then Hispaniola on very similar to the track Fred took:

Even though she is weak, this is really tough for Haiti though as they had Fred a few days ago, today they had a major magnitude 7.2 earthquake, and Grace is going to be adding to a lot of rain sometime around Monday! 

Tropical Storm Grace may be weak, but she is definitely a TS as we saw from the vorticity (circulation) maps above. 
The Caribbean air is not so dry as the Atlantic SAL and the waters are warm - both reasons for her to intensify and we see heavy convection because of this:

She is definitely dumping a few buckets of rain over that part of the world! Hope you have your raincoats out!
Although there isn't much wind shear, her very fast forward speed means that her vertical structure is a little skewed- which we can see from the vorticity maps above because the red blob in the 500mb map is a little to the southeast of the one in the 850mb map. Her fast speed also means she won't be away from land for long. So, until she slows down a bit, she won't really intensify much and she may not have time to get very strong before she starts to interact with land again. Like Fred, we'll see if she even survives depending on how much land she runs into. 

And to wrap up today's sophisticated post...

Toodle pip, 




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 local 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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