Re: Models All Over
Posted by Jackstraw on 9/4/2009, 1:10 am
Midlevel wind.  That is the one layer that can't be sampled over water.  They use math to estimate the midlevels using 850mb and 200mb level winds which they can pretty much see with the satellites.  2 days ago it looked like upper level shear was blowing the convection east.  From Dr. Masters blog that day .....

Wind shear analyses from the University of Wisconsin diagnose a moderate 10 - 15 knots of shear over Erika, a decrease from yesterday. SSTs are warm, 29°C. Why, then, is Erika so disorganized? The trouble with the various wind shear analyses we use is that they take a crude average of winds over a thick layer to arrive at an average shear, and this large-scale average shear does not capture thin layers of shear that can dramatically affect a tropical cyclone. Upper air data from Guadeloupe and Saint Martin from last night show a complicated shear pattern in Erika's region, with 30 knot winds out of the south to southwest at 200 mb height, nearly calm winds between 300 - 500 mb, and northeasterly winds of 10 - 20 knots from the surface to 500 mb. Some extremely dry air with humidities near 10% was present in a thin layer near 600 mb on the Guadeloupe sounding, so dry air from the Saharan Air Layer is probably being injected by a northeasterly jet of wind into the core of Erika. The shear of 30 knots at the top of the storm is ripping away the heat and moisture Erika's thunderstorms are lifting there, and the result of the shear and dry air is a very disorganized tropical storm.


The models don't handle this mid level shear as well.  We have seen this with several storms.

When you look at the shortwave IR tonight....

http://www.ssd.noaa.gov/goes/flt/t2/flash-ir2.html

It is definitely decoupled as they like to say.  The LLC looks open as there are no west winds visible.  But that intense mid level cyclone over the Islands certainly gets my attention.  Unfortunately it hasn't gotten the NHC's.  So the 12Z GFDL will probably initialize with nothingness and present us with nothingness...or will it?  

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Models All Over - DougInBrevardForce10, 9/4/2009, 12:37 am
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