Tuesday, August 24, 2010

Tropical Storm Danielle and Atlantic Blob: August 24, Update A

Tropical Storm Danielle:
Hee hee... I knew today was going to be a fun storm-filled day! and I also knew I shouldn't have written that girls are well-behaved because that was just asking for trouble, wasn't it? Well I always was more inclined towards the phrase "well-behaved women rarely make history" (Laurel Thatcher Ulrich). ;-)
Today Danielle threw the hurricane forecasting community a curve-ball and everyone is running around trying to work it out. Don't you love it when that sort of thing happens? She was developing quite nicely and even had moments where we could see a lovely eye earlier today, and then something changed. No-one knows exactly what (yet), but it resulted in her falling apart quite drastically! Isn't it cool that there are still such big mysteries out there waiting to be solved? :-)
Apparently the dry air that I thought yesterday wouldn't have much of an impact was the culprit. Over a handful of hours, it brought her down from a Cat 2 hurricane with winds of 100mph (cat 2 range: 96-110mph) to a Tropical Storm with winds of 70mph. We've seen dry air destroy storms before, but the unusual thing here was that her center was so well insulated by moist air (or so it seemed) that it didn't seem likely to have this much of a punch. Clearly something went on in the layers within a storm that we can't see with a satellite. Or (and I'm speculating here), maybe it was something to do with her forward motion, which was really really fast for a cat 2 storm. I'll have to do some digging on this. Oh I do like a good real-life mystery. :-)  
Before I carry on, her vital statistics from the NHC 5pm advisory: she's at around 16.5N, 48.2W with a central pressure of 993mb. Winds are at about 70 mph (so she's a strong Tropical Storm) and she's moving WNW at 18mph.
Although she's a TS again, there's a very good chance she'll regain strength. Her vorticity is strong throughout the entire troposphere. In fact it's strengthened since yesterday which means that the basic storm structure is good, even if she's struggling with the convection issue a little because of surrounding dry air. This is the sort of structure I'd expect to see with a major cat 3 hurricane. She's over water that's warm enough to sustain her (over 29 deg C) and there is only a little in the way of wind shear. Assuming whatever conditions that caused her to fall apart don't re-appear, I think she'll restrengthen. This is in agreement with the NHC. Having said that, there is still some dry air in front of her, to her north and west. So restrengthening depends a bit on if she can again wrap herself in a blanket of water vapor or whether the dry air will continue to get into the center. I suspect she'll re-strengthen.   
As for track, as I said yesterday she had two options - to move towards to west or to slow down. She certainly didn't slow down but has, indeed, been moving on the western side of the center of the cone, so the forecast track has shifted westward and as of today Bermuda is within the cone. I hope you guys are getting ready for a visit! Hopefully you'll just get some light rain and a bit of breezy weather.
Atlantic Blob:
This little blob is still just out of sight for most of my maps. Although I can now see the vorticity properly, I can't see how strong the convection is yet. The circulation is good in the lower half of the troposphere, but nothing in the higher levels. The NHC have had it at a 90% chance of developing into a Tropical Depression for the past couple of advisories! I think it's already a TD, so I don't know what they are waiting for. It doesn't mean it's a named Tropical Storm yet, but it looks like it has closed circulation.
What an interesting day! (if you are a stormaholic like me). Can't wait to see what she'll do tomorrow... oh... er... I'm supposed to be telling you what she'll do tomorrow, aren't I? ;-)
Ciao for now!
p.s. meant to say this a few entries ago, but if you have any questions please let me know. I assume people have been reading this for a while, so I throw in jargon words like 'troposphere' and er 'storm' ;-), having explained them in earlier entries. But if you missed it, please ask.
Blog archives at http://jyotikastorms.blogspot.com/

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 was there and was going to "run away, run away" (Monty Python), I'll let you know.

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