Saturday, July 25, 2020

Tropical Storm Gonzalo, Tropical Storm Hanna, Hurricane Douglas: July 24, Update A

Aww, bless him! Dr. Fauci really doesn't want anyone to catch anything this year...  

(adapted from a tweet I saw) ;-) 

Tropical Storm Gonzalo
He continues to behave - continuing to weaken from his interactions with the Saharan Air Layer. He is officially still a TS with winds of 40mph, central pressure 1009mb, but officially he's barely one as the wind range is 39-73 mph. There is a plane in the system at the moment investigating, so he could be downgraded to a Tropical Depression before even getting to the Caribbean. However, he still has some strong convection, which we can see from the satellite imagery: 
And there is still some circulation in the lower half of the troposphere. 

He currently at 10N, 57.1W (finally, making that WNW move), so as he gets close to land (or island), he will weaken even more and the NHC have now downgraded his forecast and expect him to dissipate over the weekend:
Not much more to say on him for today other than there will be a bit of rain, maybe a light breeze if you are in that neck of the woods. 

Tropical Storm Hanna
She's currently at 27.1N, 94.8W, heading W at 8mph. She's certainly got stronger since yesterday and now has winds of 65mph, central pressure at a low 992mb, which makes her a strong Tropical Storm (TS range: 39-73mph). 

I've been going with the NHC forecast track for this one and it's pretty consistent - making landfall in southern Texas somewhere near Padre Island on Saturday (tomorrow): 
I do think they have the center slightly too far to the east and it should be closer to 27.1N, 95.5W but I'm sure they'll fix that soon enough.

The NHC intensity forecast is now in alignment with my thinking - she'll be a hurricane at landfall. In my opinion, she is already a hurricane, so she may even make it to cat 2 before she makes landfall! There is very little wind shear and the water is warm. There is some dry air in the lower and middle levels of the troposphere, so that may keep her as a cat 1 storm before landfall, but that's about all I see.  
Her circulation (vorticity) is really strong throughout the entire troposphere, which is a signal of a hurricane. You know, I think it's time for a <Science Alert!>.... 

<Science Alert!> Vorticity: I keep dropping this magical word that tells me all about the storm structure, but what is it? Well, a storm has 'circulation', and it's pretty obvious what that is, right? It simply means that a storm is going around a central point, like a carousel. Vorticity, is essentially the way we measure the amount of circulation that a storm has. It's a very useful tool and I've used it for ages - next to a corkscrew for opening yummy wine bottles, it's my favourite (with a 'u') tool during hurricane season. ;-)

Although satellite imagery is one piece of the puzzle, the biggest clue about what sort of storm we have is the vorticity and what it looks like in different levels of the troposphere, because that gives us a glimpse into the structure of the storm. 

All types of stormy weather have a recognizable vorticity signal in the troposphere. Like a fingerprint, you can figure out what sort of storm system you have if you know what and where the vorticity is. The vorticity for low pressure fronts looks different compared to tropical storms. For low pressure fronts, the vorticity stretches out in a long line. For proper, grown-up, tropical cyclones, the vorticity is confined and generally circular. 

You can also tell how strong a tropical storm is depending on how strong the vorticity is and how high into the troposphere that signal can be seen. A Tropical Storm ALWAYS has a vorticity signal that reaches the middle of the troposphere (around 500mb) because this indicates that there is some deep convection (aka big thundery clouds). A Hurricane ALWAYS has a vorticity that reaches the upper level of the troposphere (around 200mb) because this indicates even strong convection and activity<End Science Alert!> 

We have a couple of storms out there, so let's have a look at the vorticity signals for TS Gonzalo and TS Hanna.

<Technical Alert!> Vorticity Maps:

Here is the vorticity map for 850 mb (almost the lowest level of the troposphere): 

You can see the signal of TS Gonzalo just off South America - the orange splodge (technical term), very conveniently covered by a Tropical Storm symbol. And you can also see the signal for TS Hanna in the Gulf, which is a big red (almost white hot) splodge - also conveniently covered by a Tropical Storm symbol (whoever is dropping those symbols has very good aim, don't they? ;-)) Green is very mild vorticity, yellow is a little stronger, orange is fairly decently strong, red is very strong, and white is really super-duper strong! Already you can tell that Hanna's circulation (vorticity) is stronger in the lowest levels of the troposphere compared to Gonzalo's circulation. 

Now let's look a little higher in the troposphere. Here's the map for 500mb (the middle level of the troposphere):

Again, you can see the difference between TS Gonzalo and TS Hanna - actually, in this case Gonzalo's mid-level vorticity isn't in alignment with his lower level. This indicates that the vortex isn't quite in alignment, and is frequently (but not always) associated with wind shear. TS Hanna meanwhile still has almost white hot vorticity at the mid-levels, meaning she has strong circulation. 

And here's the map for 200mb (the upper levels of the troposphere):

In this upper level map, you don't see any signal for Gonzalo. That's because he's not a hurricane, or even close to being a hurricane - there is no upper level circulation. However, Hanna is already at a yellow level, which means she's already a hurricane.  And the stronger the signal is at these lofty high levels of the troposphere, the stronger the hurricane. 

These amazing maps are produced by the University of Wisconsin-Madison's Cooperative Institute for Meteorological Satellite Studies - and a jolly good job they do too! To see them for yourselves in the future, click on the link above. If you followed my instructions on how to find data on the SAL a few days ago, this page should look awfully familiar. As before, go to the second map on the page (Regional Real Time Products) and click on the area of the world you are interested in. For the examples above, I clicked over the North Atlantic. From the drop-down menu, chose 'Winds & Analyses'. In the top panel, you'll see a whole array of buttons - including the 850mb, 500mb, and 200mb Vorticity. Clicking on those will give you maps like the ones above. This is definitely one of my favourite websites! You can even go back in 3-hour chunks of time and see the vorticity for a storm evolve or move around. It'll provide you with hours of fun and entertainment - all from the comfort of your own living room! :-) <End Technical Alert!>

For those who live north of the point of landfall, the storm surge will be high as she pushes water on shore. NOAA's Tides & Currents website: will give you storm surge information for your local area. To see instructions on how to navigate this, read the Technical Alert in this TS Cristobal post. For Corpus Christi, the storm surge is already almost 1.5 ft above normal... 

More on this one tomorrow. 

Hurricane Douglas
Meanwhile, over in the Pacific, Hurricane Douglas has calmed down a wee bit. He is now 'just' a major cat 3 storm with winds of 115mph, central pressure of 971 mb, which makes him a weak cat 3 storm (cat 3 range: 111-129mph). He still has a strong eye, but his convection is a lot lighter than yesterday's deep red and orange cold cloud tops:

This is because he has moved over colder water now - temperatures are around 25 deg C. There isn't much wind shear, but there is some drier air ahead of him which is also playing into his weakening as you can see from the south and southeastern side of the storm, which is pulling that dry air into his system. 

He is currently at 18.2N, 145.9W. He's heading WNW at a very rapid 20mph and will reach the Hawaiian Islands on Sunday: 
He'll remain over cooler waters as he approaches Hawaii, and if that dry air continues, he may be a cat 1 as he gets close to the islands on Sunday. There is some wind shear ahead of him - closer to the Big Island - so if that persists, that will also help bring him down a notch. By the time he gets to Oahu, he may just be a Tropical Storm - but let's see whether he gets downgraded to a cat 2 tomorrow first. A Hurricane Hunter plane is currently gathering data from the system so that will help really get a handle on his intensity. 

Now you've learned about vorticity maps...  in the mid-level (500mb) and upper level (200mb) of the troposphere for the vorticity map for Hurricane Douglas, you can also see the vorticity for Hanna (unmarked on these Pacific Ocean maps): 

See the stronger vorticity signal for Douglas compared to Hanna's in the upper troposphere? An indication of a stronger hurricane. Easy, right? 

Until tomorrow!

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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