Saturday, August 19, 2017

Tropical Storm Harvey: August 18, Update A

A public service announcement: If you like vanilla ice cream (or vanilla anything), you better stock up now. I say this not just because I am an ice-cream pusher (although I have been known to ‘encourage’ my friends to partake) but because the price of vanilla has gone up by ~500% because Madagascar, where 80% of the world’s vanilla is grown, was hit by a category 4 cyclone in March (Cyclone Enawo) resulting in a very poor vanilla harvest this year. A cyclone is a tropical storm so it is the same type of storm as a hurricane; it is called a cyclone because it is in the Indian Ocean, just as a tropical storm in the western Pacific Ocean is called a typhoon. 

As I eat my vanilla ice cream I think that today we’ll just pop in to see how Tropical Storm Harvey is progressing. We are ditching the Atlantic Blobette for now because it is not doing as well as it was yesterday; it has no circulation in the mid-troposphere anymore which is pretty much as expected.

Harvey is currently at 13.7N, 64.1W, heading W at 18mph. Central pressure is 1005mb and winds are still 40mph, which means he is officially barely a Tropical Storm (TS range: 39-73mph). He has crossed the Leeward Islands and is now in the Caribbean, but again as expected, he hasn’t really developed much so far because he was interacting with the islands and because of wind shear.

The convection has improved today, and we can see some very strong thundery weather (in the red and gray areas) in the infrared satellite imagery:

This increase in convection is because he is over some very warm ocean water. The sea surface is 28-29 deg C, and the upper 100-125m of the water is warmer than 26 deg C, which means that even though he is churning the surface, the water underneath is also warm.

But he is still experiencing some wind shear and although there is some good circulation over the entire lower half of the troposphere, you can really see the wind shear because the red splodge at the 850mb (lower troposphere) is definitely offset from the 500mb (mid-troposphere):


So, again, in this case we see a battle between the ocean and atmosphere, with the ocean pushing him to develop and the atmosphere really pulling him back. In my opinion, he will develop but it will be slow until he gets away from that wind shear (sometime tomorrow) and his structure has a chance to improve.

The NHC track takes him more or less westward for another day at least, and then a gradual shift to WNW and NW, and across the Yucatan.

That’s it for today. Time to get back to eating some more vanilla ice cream before it becomes an unaffordable luxury! 

Ciao until tomorrow!
J.

Blogs archived at http://jyotikastorms.blogspot.com/
Twitter @JyovianStorm
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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. 



Friday, August 18, 2017

Ex-Hurricane Gert, Tropical Storm Harvey, the Atlantic Blobette, and the Atlantic Stormling: August 17, Update A

I’m going to start by saying that Jaffa Cakes are yummy. Although there is a serious philosophical discussion on whether they are cakes or biscuits, it doesn’t really matter… they are pretty scrumptious. Just thought I’d make sure my friends on the Gin and Cake podcast (@ginandcakepod) knew my position on Jaffa Cakes! ;-)

And to continue with things I mentioned yesterday… as we saw Gert was winding down and she has now pretty much gone bye-bye. She was last seen somewhere north of 45N, 45W drifting off to the northeast, so this is my last update on well-behaved Gert.

Tropical Storm Harvey
As expected, the Atlantic Blob that we saw yesterday that was heading out of the dry area of the SAL and over an area of warmer ocean waters did slowly develop into a Tropical Storm. Harvey is currently at 13N, 58.1W, heading W at 17mph and is approaching the Leeward Islands:

His central pressure is 1005mb, and the winds are an estimated 40mph so he is barely a Tropical Storm (range: 39-73mph). I would agree with this because the circulation has improved today, as we can see from the vorticity maps. Here are the maps at 850mb (lowest level of the troposphere):

and 500mb (middle of the troposphere):

There is no signal at the highest level of the troposphere (200mb), so we know he is definitely not a hurricane. Interestingly, you can see the offset between the lowest level and mid-level maps in the center of that circulation, which is an indication of wind shear. Because of this, and because he is about to interact with the Leeward Islands (which are a little hilly!), he won’t really develop much very quickly in the next day or so. But he is over warm water, so once he clears the islands, I expect some slow development.

From the NHC track, it looks like he will stay to the south and move across the Caribbean.

Atlantic Blobette
This one is at around 15.5N, 48W, heading WNW at 20mph. She hasn’t really managed to gain too much traction, although from the vorticity maps we see that she has some circulation over the entire lower half of the troposphere. She is struggling a little because of the convection, which is quite weak at the moment because she is in a region of dry and dusty air.

She is about to move over an area of slightly warmer water which will help her to develop some of that convection, but the wind shear will also increase in a couple of days, so it really is a battle between the ocean and atmosphere in this case! Given that she has some circulation, I think the ocean may win out in the short term (a day), and then the atmosphere will take over with the wind shear and dry and dusty air and inhibit her from developing too much more beyond that.

Atlantic Stormling
And then there’s that poor little Stormling, currently at around 13N, 30W moving generally north-westward at around 20mph. The circulation is very weak and it is quite entangled in the Saharan Air Layer:

I don’t expect anything much to happen in the next few days – not until it clears some of that SAL at the very least. I think I’ll hold off on any more on this one until something happens.

And finally, I have to say that the world is definitely on the wobbly side of wonky these days! My condolences to Spain!  

That’s it from me for now. Over and out until tomorrow!
Toodle pip!
J.

Blogs archived at http://jyotikastorms.blogspot.com/
Twitter @JyovianStorm
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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.