Sunday, August 05, 2012

Tropical Storms Ernesto and Florence: August 5, Update A

Dear NBC Olympic commentator for the equestrian sports, when it is raining the British say “it’s chucking it down” not “it’s shucking it down”. It is rain, not corn. Thank goodness I am now watching the civilized sport of tennis (my favourite) with proper commentary by John McEnroe. Wimbledon final déjà vu… Murray versus Federer at the All England Club! Murray leads by 2 games in the 1st set. Come on Murray!!

TS Ernesto
Ernesto is officially at 15N, 76W, moving W at 22mph. Winds are 50mph, central pressure 1006mb.

The good news is that I was wrong! J Ernesto has weakened since yesterday, not intensified as I thought he would (although I still maintain he was a borderline cat 1 storm during a portion of the day). Having looked at all the data, here’s why I think this happened. (Murray wins first set! J). From the oceanic perspective, sea surface temperatures are still warm (27-28 deg C), but he did pass over a small region where the sub-surface waters only had water warmer than 26 deg C in the upper 50m which would have slowed down his intensification a bit. He has now passed this and is back in an area where the warm 26 deg C waters are in the upper 150-175m. From the atmospheric perspective, he still has dry air in front him which would inhibit his development. Wind shear has been and continues to be quite low, so this wouldn’t have hindered him. He is interacting a little with land which may have inhibited him a bit, however I think the biggest factor is that the circulation that was developing in the upper troposphere was suppressed. (Woohoo… Andy Murray won the second set!!)

<science alert> A storm is a low pressure system at the bottom of the atmosphere (close to the ground). Air flows from high to low pressure, so it flows into the center. We call this low level air flow inflow or convergence (converging to the middle). But if it flows in from all sides, then where can it go? It can only go one way, and that is up. At the top of a tropical storm it has room to flow outwards… so, interestingly, a tropical storm with a good structure actually has high pressure at the top because the air is flowing out horizontally from that point. We call this outflow or divergence. A good storm has low pressure at the bottom and high pressure at the top. But to set this up there has to be ‘room’ around the top of a storm for the air to flow out, which depends on the conditions of the surrounding atmosphere at the top. With Ernesto, it looks like the conditions in the upper troposphere were not good enough to continue setting up the outflow circulation and that suppressed the entire storm from intensifying. You can look at the lower level convergence here: and the upper level divergence here: For a good storm structure, both would show concentric circles. The more (closer and circular) the circles, the better the structure. <end science alert>

<taking a break for English Breakfast in keeping with the flavor of the morning> (YES! Murray just broke Federer’s serve in the 3rd set, 3 games to 2!). Gold Medal Point … and… he WON! Hurray! Hurray! Is it too early for Champagne? ;-) J J (I knew this was a momentous day!). J

The really good news is that because the atmosphere is not playing along, the ocean will not make Ernesto as strong as he could have been so he will remain a Tropical Storm (at the most a cat 1) all the way to landfall.

Because Ernesto’s structure is so wishy-washy, it is difficult to figure out exactly where his center is at the moment. The NHC did have it too far north yesterday at 15.4N. Since then they have moved it south, and it is now at 15N (actually 15.1N since I started writing). I was also correct in the track which they have moved a little farther south again. It is now going to make landfall in Belize on Tues night/Weds morning.

TS Florence
Meanwhile, little Florence out there in the Atlantic is officially at 16.5N, 35.6W moving W at 14mph. Her winds are currently estimated to be 60mph, central pressure 1001mb. She isn’t doing very well at the moment. The circulation and convection have deteriorated, as  you can see in this satellite image:

I don’t think the winds are as strong as 60mph, her center is somewhere around 16.8N, 36W, and she is moving more in a WNW direction. I’d estimate winds to be closer to 40-50mph – so a very weak storm. Although there is low wind shear, she is actually passing over a region of colder sea surface temperatures of less than 26 deg C (colder than what we need to sustain a tropical storm). Depending on her track, if she continues westward she may head back to warmer waters soon and put on a new coat then.  However, if she continues WNW/NW, she may stay over cooler waters and just fizzle out in the Atlantic.

That’s it for now. I have a very busy day ahead… celebrating Andrew Murray’s win and then watching him in the mixed doubles later! J

Toodle pip and tally ho!

Blogs archived at
Twitter @JyovianStorm

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.

No comments: