Tuesday, November 10, 2020

Tropical Storm Eta and Subtropical Storm Theta: November 9, Update A

Well well, the most 'named' storms in a season hey? This season now ties with 2005 for the most named and numbered storms on record - 30. 

<Minor Rant Alert!> However of course back then in the days before satellites some of the storms in today's day and age would not have been detected - or even noted as being significant by the NHC - especially not very short lived few hour storms such as 2020's Subtropical Storm Alpha which was a named system for less than 12 hours and only had winds greater than 39mph for about 5 hours!! That's just a blob at that point! I'll do a proper analysis of this season once it's over, but I definitely don't agree that all the storms named this season were proper storms which is really annoying because it masks the actual trends when things are named willy nilly and it messes up the scientific conclusions! To get around this, the NHC need to introduce a process for 'un-naming' storms in such cases!<End Minor Rant Alert!>

Tropical Storm Eta

It's still officially a Tropical Storm and the entire forecast was downgraded from Hurricane to Tropical Storm for its lifetime. I'm not sure I'm in complete agreement with this downgrade but I'll come to that later. 

It is currently at 23.2N, 85.2W, heading SW at 9mph: 

The forecast is that it will continue south for a little longer and at a slower pace before doing a bit of a u-turn and heading back to the north. 

Winds are currently 50mph, central pressure is 995mb, which makes it a weak Tropical Storm (TS range: 39-73mph). However, the convection has definitely picked up in the last few hours: 

This is because it's over some very warm water (sea surface temperatures are warmer than 28 deg C), and also over the teeny little bit of Loop Current where the upper ~125m of the water column is warmer than 26 deg C:

This suggests to me that this is not a weak Tropical Storm anymore, but a strong one, possibly with winds of around 65mph. I think there's a small window for it to become a cat 1 storm before it gets too far into the northern Gulf where it will run into a couple of things that will knock it down a notch. 

You can see from the map of the warm water above that in the northern Gulf, the warm water is be shallower - that's one factor indicating that it should get weaker.  

There is also very little wind shear at the moment, which is why it is developing. However the northern and eastern Gulf has quite a bit of wind shear - another weakening factor as it moves north. 

There is some pretty good vorticity throughout the troposphere at all levels. It's not very well defined as we've seen in all the other Tropical Storms, but it's definitely more confined and distinct than the interloper Theta (see below)!  

For your reference, the vorticity map in the lower troposphere (850mb) is:

The vorticity map in the middle troposphere (500mb) is:

And the vorticity map for the upper troposphere (200mb) is:

This brings me to...

Subtropical Storm Theta

Sigh. I can't believe they think this is tropical in any way and went ahead and named this one at this stage. They must have drunk too much champagne this weekend!

As you can see from the vorticity structure above, there is no part of the troposphere that has a tropical storm signal in any way - it's all a front (an elongated line of vorticity - the long red streak that is stretching to the northeast from the subtropical storm symbol in the middle of the Atlantic). They are calling this a subtropical storm because it's getting it's energy from the atmosphere, not from the ocean.  A tropical storm needs water warmer than 26 deg C to get its energy from the ocean - the water temperature under Theta is too cold for a tropical storm and is around 23 deg C at the surface. You can also see that there is no water warmer than 26 deg C from the water depth map above. 

Still, it's another one that's been named when it shouldn't have been and that's what we have now. It's at 28.8N, 40.3W, heading E at 15mph. 

Officially winds are 50mph, central pressure is 1000mb, which officially makes this a weak Tropical Storm - the same level as Eta actually, even though Eta is clearly stronger! As for looks... 

It also looks nothing like Eta - at least not today. Clearly there is a lot of wind shear and you can see the front - the straight line of clouds. This is really not a Tropical Storm by any means - but we'll see what happens tomorrow. The NHC think that it will develop into a TS by then. Hmm. 

That's it for now!



Twitter:  jyovianstorm

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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