berrywr
(Weather Analyst)
Sun Aug 26 2012 06:44 PM
Tropical Storm/Hurricane Issac - 26/12Z Upper Air Analysis

I have a date cutting my yard when I'm done...my apologies for being a bit later than usual..however, it is Sunday! The models continue to be in two camps; with the ECMWF and UKMET being in the east camp and the GFS and it's kissing cousins making LA/MS having Katrina flashbacks. At 500 millibars the upper ridge axis I have talked about over the past 36 hours continues to remain in place and is building and heights have now risen to an average of 5900 meters with a 592 dm center over Southern Alabama; the axis is slightly inland and extends the entire length of the Gulf coast. The upper low over VA has cut itself off further aloft at 300/200 millibar which is evident on water vapor imagery and shear analysis reflecting about 20 to 25 knots from the SSW to NNE out ahead of Issac; it has weakened but nevertheless should inhibit rapid intensification despite ideal conditions in every other way. What the ECMWF and UKMET are picking up is what remains of an earlier in the week longwave trough which has lifted out quite nicely but what remains is this upper low and it's adjoining shortwave trough which lies just west of Charleston, SC southwestward to a position between Tallahassee and Jacksonville where there is a COL in the northeastern GOM where the upper ridge axes and shortwave trough and Issac's inverted trough meet. The other player in all of this is a shortwave trough in the middle part of the country expected to move east and deepens the longwave trough again along the eastern US. I'm still waiting for whether an upper ridge sets up shop in the Inter-Mountain West as models continue to advertise. There is a very small window of opportunity if Issac opts to make its welcome along the Alabama/Florida coast; otherwise it does appear that the narrow ridge axis along the Gulf coast will be strong enough to; one, the trough in the plains states to bypass the cyclone and two, steer the system west and then northward as the models have been advertising with this IM west upper ridge center that has yet to develop. Radar imagery out of Key West has Issac moving generally NW but there has been a bit of wobbling to the NNW. Y'all have fun!


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