Tuesday, August 28, 2012

Hurricane Isaac and TD11: August 28, Update A

Hurricane Isaac
Landfall in Louisiana is imminent! Actually, from the New Orleans radar (http://radar.weather.gov/ridge/radar.php?product=N0Z&rid=lix&loop=yes) and the visible satellite image (below) it looks like he is moving on-shore on the squiggly bit that sticks out into the Gulf (the Mississippi Delta)!

He was officially upgraded to a hurricane in a special 11.20am (CDT) advisory this morning… although I saw an eye when I was watching him at 6.30am (EST) this morning (I had turned on the computer to see what he was up to before I even had a cup of tea this morning. It was quite uncivilized! ;-)). Here is the infrared satellite image of him that I grabbed at that time – - the eye is clearly visible, even though he looks like a half-eaten (orange and red) biscuit (or cookie if you are in the US):

The northern half of him was all dry dry air, with convection only on the southern side, over warm water.

The NHC issued a second special advisory at 6pm CDT (i.e when I grabbed the top satellite image) to let us know that the center was nearing the coast of LA. At 7pm CDT, he was officially at 29.0N, 89.4W, moving NW at 8mph. The NHC increased his winds to 80mph, which makes him a weak-to-middling category 1 storm (range: 74-95mph). Central pressure 970mb.

Although this increase in wind speed is an estimate they made, I agree with it because his convection has improved. Here's the latest infrared satellite image of him, but this time it is a view of the entire eastern side of the US:

You can see three things from this: first, the red areas (and thundery weather) has increased since this morning; second, the dry air is not chopping him in half anymore – the convection has spread around to all sides; and three, Isaac is still causing convection over eastern and central Florida, as well as parts of Georgia and the Carolinas (because of wind shear). The long arm of Isaac!

Given that he is almost half on land, it is unlikely that he will get much stronger. The circulation (vorticity) data I normally look at seems to be a little outdated at the moment, so I can’t see if his circulation has started to deteriorate yet or not.

Now for the surge. Shell Beach in Lake Borgne, LA, is now 9ft above normal and New Canal Station in Lake Ponchartrain is about 3-3.5ft above. Grand Isle (LA) on the Gulf Coast is about 2 feet above, Bay Waveland Yacht Club in MS is 6ft above normal, Pascagoula (MS) and Dauphin Island in Alabama are both 4ft above, and most of Mobile Bay is 3.5 ft above (but it looks like its dropping now). In Florida, Pensacola reached a maximum of 3.5 ft above normal.

Tropical Depression 11
This guy has some circulation in the lowest half of the troposphere, but it is not very cohesive yet. He is officially at 23.8N, 43.9W, moving WNW at 10mph. Winds are 35mph, central pressure 1008mb. There is some decent convection, which looks like it is nearer to 25N, which shows that there is some wind shear impacting this system. They think he will be a Tropical Storm tomorrow. If the circulation improves, this is quite possible. The next name is Kirk.

Good luck to all those who still have to deal with Isaac! (including the east coast of Florida – I heard there was flooding in Stuart, Florida).

I might be back later with the official word on landfall.


Blogs archived at http://jyotikastorms.blogspot.com/
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: