Saturday, August 25, 2012

Tropical Storm Isaac: August 25, Update A

Aww… Astronaut Neil Armstrong passed away today. A great inspiration, a great achievement, and a great small step for humankind! Thank you Neil. Alas, a major US news network was a little clueless and didn’t check their facts before releasing the story... dear news network: 1. Neil Armstrong was an astronaut, Neil Young is a musician. 2. Neil Armstrong will not be reading your headline, Neil Young may be surprised to read your headline. 3. Neil Armstrong was the first person to walk on the moon, Neil Young had an album called Harvest Moon.

Coincidentally, Neil Young also has a song called “Like a Hurricane”, and so the link has been made…

Intensity: The islands of Hispaniola and Cuba have taken a bit of toll on TS Isaac and winds are now 60mph, with a central pressure of 997mb. This makes him a mid-range Tropical Storm (range: 36-73mph).  The circulation (vorticity) he had in the upper levels of the troposphere before getting to Haiti has pretty much dissipated, leaving him with good circulation only in the lowest half of the troposphere for now. His convection is also pretty weak compared to before he reached Haiti (where 400, 000 people had to bear the rain and wind in the tents they have been living in for the past 2.5 years (!!), after the 2010 earthquake!).

As you can see in the latest satellite image, there are very few strong thunderstorms or tornadoes at the moment (i.e. no red and gray areas):

This reduced circulation and convection keeps him solidly as a Tropical Storm. The other factors that are currently inhibiting his development are some really good wind shear north of Cuba/Bahamas/Florida and dry air to his west. You can see the impact of this in this satellite image of water vapor, with clouds streaming off to the northeast and east:

The sea surface water is a nice warm 30 deg C, but only the upper 50-60m of the ocean has water warmer than 26 deg C  to help him slowly intensify if he didn’t have other things working against him.

Track: I think Tropical Storm Isaac did head slightly more north of NW last night as he crossed Haiti, via Port-au-Prince, and is now on the northern side of Cuba, right along the coast. That portion (crossing Haiti and Windward passage) of the track shifted a little east and north. His official center is at 21.3N, 76.0W, heading NW at 21mph. I agree with the official track that he will continue to move generally NW.

The models are predicting the high pressure to rebuild (I mentioned this as a possibility in my fourth scenario yesterday), which is why the forecast track takes him westward and into the Gulf. They are not quite sure how much it will rebuild yet or where he will be relative to that, hence there is uncertainty in the landfall. At the moment the pressure fields I’m seeing will allow him clear passage to the eastern side of Florida (so he may even make a personal visit to the NHC in Miami), but the models are all in alignment, so I suspect that high will rebuild. I hope to have updated data later this evening.

The best case scenario for everyone in the entire region (Cuba, Bahamas, Florida) is that he continues to skirt that northern Cuban coastline (or moves onshore a bit). This would be the least impact on Cuba and would also hinder his development. At the moment there is also the wind shear and dry air he is dealing with, which means it will be difficult for him to intensify much until he clears Cuba.

I went and bought some more ice cream. Just in case. ;-)

Until later my friends!

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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.

1 comment:

Gruntled Guy said...

And here I thought Neil Armstrong was the just-busted cyclist who was so performance-enhanced that he could have ridden his bicycle to the moon, never mind the Alps.