Thursday, July 30, 2020

Tropical Storm Isaias: July 29, Update A

Tomorrow is a big day - the third launch to Mars in as many weeks (ish). It'll be NASA's turn with Perseverance. Ah, I still remember the first image from the Curiosity Rover... 
I was not overly surprised. ;-) 

So, they finally tossed this storm to the pterodactyls and took him from 'Potential' to 'IRL' (In Real Life). He's now finally achieved Tropical Storm Isaias (pronounced: ees-ah-EE-ahs) status. He is currently 'centered' at 15.8N, 76W, officially heading WNW at 20mph. 
They have consistently been moving his center south, which is why he didn't head to Puerto Rico, as they expected he would yesterday: 
Instead, in fact, his current center is directly south of Puerto Rico and quite far outside yesterday's Cone of Uncertainty - making this one of the worst track forecasts we've seen in a very long time (years). As I said, I think that's because they had his center too far north by at least 2 degrees latitude in the first place. 

However, for some reason they are still insisting that his track will head to Florida, which means that if he is to keep within his Cone of Uncertainty for today, he's going to have to move NW within the next few hours, not WNW. Clearly there is still some confusion on the track for this storm. From the NHC: 

"Since the cyclone is expected to move over Hispaniola on Thursday  some weakening is likely within the next 24 hours.... Also, a re-formation of the center to the north of Hispaniola may occur. 

The scatterometer data show that the center of the system is south of the previously estimated track, so there is a lot of uncertainty in the initial motion estimate of 285/17 kt." 

(285 is the degrees on a compass... where 270 deg is due W, so 285 is WNW). 

I'm not sure how the storm is expected to move over Hispaniola AND re-form to the north. Some form of Klein tunnel, perhaps? ;-)  

I'm still not convinced he's going to head NW - I think he'll stay a little more to the south and on the WNW track, but we'll know this in the next few hours. But I do think they finally have a relatively good general area for the center - so today I agree that 'x' marks the spot. 

As for the intensity... he is currently a relatively weak Tropical Storm with winds of 50mph, central pressure estimated to be 1004mb (Ts range: 39-73mph). He does have a few buckets of rain (with some thundery weather) that he's pouring over the islands - cleaning the cars, washing the Saharan Dust away...

Interestingly, his intensity is based on consistent winds in the Atlantic! Not in the Caribbean, near his center? From the NHC:

"The current intensity is estimated to be 45 kt, but these winds are currently occurring over the Atlantic waters well to the north and northeast of the center."

But there is no doubt he would be a fully fledged Tropical Storm and from the size of him, if there wasn't any Saharan Air Layer or wind shear keeping him in check, he would be a big boy! Here's the SAL image, which really brings home how large of an area his clouds actually cover:

I estimate from south to north, those clouds cover around 1400 miles! 

But what about his intensity? His vorticity (circulation) has been improving over the past couple of days. Officially, he is a weak TS, however there is now a vorticity signal (circulation) in the upper troposphere, which indicates that he is actually quite a bit stronger than the 50mph that they have him at. Another indication of strengthening is that we see some deep convection solidifying in the center from the satellite imagery - that's because he's over very warm water (warmer than 29 deg C) with the upper ~125m now warmer than 26 deg C. His center is also quite far from the dry, dusty Saharan Air Layer, so that isn't stopping the gooey marshmallow center from developing. 

So, the bouncy ball I'd like to leave you with is that today, for the first time, I agree with the NHC on the location of his center. I think he'll continue on a more WNW track for at least another day or so. If, in the next 12 hours, he doesn't move more sharply NW then he won't be moving over Hispaniola, but instead he'll intensify further as he stays over that deliciously warm water in the Caribbean.

Regardless, everyone should be ready anyway - I have my wine and cheese so I'm ready!

Until the 'morrow!

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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