Tuesday, September 15, 2020

Hurricanes Paulette and Sally, Tropical Storms Teddy and Vicky, and some Blobs: September 14, Update A

All sorts of storms out there today!

We don't frequently see this (thankfully) but this isn't the worst it's ever been out there. For example, in August 1995, there were five named storms in the Atlantic. As for hurricanes, there are only two today... in 1892 (before satellites or planes) and 1998, there were 4 hurricanes at the same time! We are now in the 'V's already, but we went into the Greek alphabet in 2005, and we probably would have done in 1933 when 20 storms were recorded without using planes or satellites (how many may have been missed?). Still... it's a bit of a long update (with lots of pictures), so I better get on with it. :-) 

Hurricane Paulette

She's currently at 35.7N, 62.3W, heading NE at 17mph and she'll continue in this direction until she hits that invisible force field over the Atlantic and makes a sharp right turn....

She is now well past Bermuda, where she stopped for a quick visit at around 2am local time when the northern eyewall started to make landfall with winds of 90mph which made her a strong cat 1 storm (cat 1 range: 74-95mph). I think they lost power fairly quickly, so it really was a dark'n'stormy night! By 5am, the entire island of Bermuda was within the eye... 

...and by 11am she was leaving the island, although her winds had increased to 100mph by that time.

She is now a cat 2 storm with winds of 105mph, central pressure 965mb (cat 2 range: 96 -110mph). Her circulation is still very strong throughout the troposphere and you can see she has still got some convection, so I'd agree with this category of storm. 

There is some wind shear which we can see as the clouds are pulled towards the northeast. Until that vorticity starts to decline, she'll remain a hurricane. 

Hurricane Sally

That expansion we saw in the satellite imagery from yesterday's post pushed her over the edge and into hurricane land. She's currently at 28.9N, 87.6W heading WNW at a very slow 3mph. 

Her track was shifted to the east, so landfall is now perhaps in Alabama - but this is really tricky to say so assume she's going to make landfall anywhere from FL to MS. Her landfall time has also been shifted to Wednesday morning - partly because of the change in track, but also because she's slowed right down and at 3mph which means she's practically stalled! A stalled storm is not good news for a couple of reasons. First, especially over or near land, it means she'll continue to dump rain and push water onto the coastline. And Second, stalled storms are notoriously difficult to forecast as far as the track goes, alas. 

 <Science Alert!> Why would a storm stall? You have heard of atmospheric high pressure and low pressure, right?  Imagine them as hills and valleys in the atmosphere, except made of air. Now imagine the storm is a ball on this undulating field. If the path ahead is low pressure, it's like a downhill gradient and the ball will happily keep on rolling forward at a decent speed. If the path in front is high pressure, it's an uphill gradient and the ball (storm) will slow down (which is what we are seeing with Sally), or maybe move in a different direction until it finds an easier path downhill. This is why the track of a storm has so many wriggles (technical jargon ;-)). 

But if the ball gets stuck in a 'dip', it is surrounded by high pressure on all sides, and it becomes difficult for the storm to move in any direction, so it will stop where it is until the pressure fields around it change (which they eventually will do). Of course, as pressure fields change, the longer range track forecast will also change, even though the storm may not have moved far. So not only do forecasters need to predict the track of the storm, but they need to predict the entire surrounding pressure field (which means predicting the entire world's atmospheric pressure field as it is all connected) and how it will change before the storm moves again. That's where computer models really kick in - these are massive undertakings. <End Science Alert!>

So, although the track has shifted to the east... landfall could really be anywhere within that cone of uncertainty! 

She's already dumped tonnes of water over FL, AL, GA, MS and will continue to do so for at least another couple of days. Storm surge is getting higher along the eastern side as the winds are pushing water onshore. Looking at the tidesandcurrents website, Pensacola for example, is already over 2.7ft above predicted levels: 

She has good circulation throughout the troposphere as well so I agree she's a hurricane, but not quite as strong as Hurricane Paulette whose circulation is much better. Here are the vorticity maps to show the circulation from the lowest level (850mb): 

the mid-level (500mb): 

and the highest levels of the troposphere (200mb):

You can see that Paulette is definitely the best structured storm - she's white hot in the lower levels compared to Sally. 

As we saw yesterday, she had a LOT of rain and thundery weather in her, most of which she seems to have kindly bestowed upon FL/AL/MS/GA:

She still has quite a bit left in her, but she is over very warm water and she expanded so quickly because it looks like she went over an area where the warm water was deeper. There is some wind shear that is resulting in the clouds being pulled to the northeast and we can see that because there is more convective activity to the north and east of her center. She may get a little stronger, but it does look like there's more wind shear once she finally gets closer to the coast.

You guys up there... it's going to be really really soggy! 

Tropical Storm Teddy 

He is currently at 13.2N, 45W, heading W at 13mph. They expect him to make a move to the WNW any second now... 

... and towards Bermuda. But I'm not sure anyone on Bermuda has power at the moment, so hopefully they aren't too alarmed yet. We'll see if that track holds - too soon to say as the island is over 5 days away. 

Winds are 50mph, central pressure is 1002mb, which means he's officially a weak Tropical Storm (TS range: 39-73mph). However, I think he is a lot stronger than this. I think he's probably at 65-70mph. There is circulation throughout the troposphere as we can see in the vorticity maps. His convection is a little spotty at the moment, so I can see why he's not a fully fledged hurricane, but I think he is close... 

Tropical Storm Vicky

She's at 19.5N, 29.9W, heading NE at 7mph. 

Winds are officially also 50mph (just as they are with Teddy), central pressure is 1000mb, but her circulation is weaker and she is really getting hit by high wind shear:

She's trying, but hasn't quite got the convection. I'm actually surprised that they have her and Teddy at the same level! Clearly they are very different and he's much stronger. They think the wind shear will stop her from developing too much. 

As for the Blob in the Gulf - they should just remove that. It's a non-entity. They should also remove Rene. And that leaves the Blob in the Atlantic that just came off Africa - that has a 30% chance of development. It does have some circulation in the lowest level of the troposphere, so keep that, by all means. 

That'll do for today!

Toodle pip,


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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