Friday, August 24, 2012

Tropical Storm Isaac: August 24, Update B

What a dilemma… vanilla ice cream and raspberries, pretzels with nutella, or wine and cheese? Hmm. It’s Friday. Maybe a light liquid dessert is called for... a yummy bourbon cream perhaps.  

Tropical Storm Isaac
Officially he is at 17.3N, 72W, heading NW at 10mph. Observations from a plane found the central pressure to be 992mb and winds of 65mph, making him a strong Tropical Storm (TS range: 39-73mph). After many days of grumbling, it is so nice to be able to say that I think this is almost absolutely spot on! ;-) (the only thing I’m not sure about is the NW motion… he might be heading more NNW, but that could just be a temporary thing).

Although the wind speed has increased to being almost a border-line hurricane, his convection has decreased. Here are two infra-red satellite images that show the level of convective activity in him – one I grabbed at 3.45pm (EST) and one I just saved at 8.45pm (EST):

You can see the decrease in his convection over the last 5 hours (red is a lot of rain and thundery weather, yellow is just rain, and blue are mostly just clouds). Unfortunately parts of Haiti got a lot of rain earlier (as well as some windy weather), which they really don’t need given that people are still living in tents and they are prone to mudslides! It looks like the rain has lessened for the moment though.

His center is still over water, just south of Haiti, but it seems unlikely that he will get much stronger given the reduced convection. There are a number of reasons for this. He is interacting with Haiti, Cuba, and of course any other landmass that dares to be in his rather large grasp. There is wind shear on his northern and eastern side, and a bit on his south side too. He has dry air on his west, which is also being brought into the system.

The forecast has him crossing the southwest tip of Haiti by tomorrow morning, reaching the southern tip of Cuba by tomorrow afternoon. The track has shifted eastwards, so we are moving towards my earlier scenarios 2 and 3. At the moment the center of the cone track takes him across Cuba, the Straits of Florida, over the middle Keys and into the Gulf. I think this will shift even farther eastward.

The caveat to all of this is that if that NNW movement I’m seeing lasts, then he will make landfall earlier and is heading towards Port-Au-Prince. He will be over Haiti for a little longer before getting over to Cuba, which may result in a decrease in his intensity. And it makes scenario 3 (that he’ll cross into the Bahamas and to the east of Florida) more possible. (N.C., you ready? I’m just saying.)

Tom says that there’s a new equation for conditions on St. Thomas: “When electrical power is on = every ting on de island does be irie”. I understood most of that (be irie? behave?). I completely understood his next message though: “Storm overall did not produce more than about 25mph winds for St. Thomas with heavy gusts coming with rain band squalls when they passed through. Center was misplaced and forced us to be over prepared and worry more. St. Croix lost some power but not all. Center was forecast to be 53 miles south of Stx but it passed over 160 miles south. Heaviest rain was last night but not constant. Still overcast this morning by hardly any wind. Tail of storm still around so more rain most likely to come.”

Lisa T. from the Keys said it was raining there this afternoon. Not quite the outer bands, but kind of connected.

Ah, yes, there is a little blob out in the Atlantic. Convection is ok but terrible circulation at the moment. I’ll report on that when/if it improves.

Oops… my pretzel stick broke off in the nutella jar. Maybe I can fish it out with another pretzel stick. Oops…that one broke in there too. Umm… maybe I’ll switch to something else and get back to my book (The Hunger Games).

That’s all for now folks!

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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.


Jonathan Welker said...

The forecast track has it curving to the east down the road. Could we may be seeing another Charlie incident if it slows down? Right now Isaac looks to be driven by the High Pressure in the West, but if the Eastern High weakens any further, could that scenario happen?

Jyotika said...

Hello Jonathan, We have had storms curve back into the west coast of Florida, like Charley did, because they are being steered around that high pressure system. However, in this case, the high is building over southern Florida (it is still building), so the storm is being moved more westward with a northward component. If that high blocks it's northward component and also it's westward movement, it would slow down (or stall) until there was a weakness in that high pressure. Those weaknesses this far north usually come from the north as a low pressure moves across the northern US. So the most likely case if it slowed down would be that it would resume moving to the NW, then N, not take a sharp turn to the northeast and into Florida.