18Z (2pm EDT) Streamline Maps

[wxman57]

Here's a streamline map with a satellite image. The streamlines are at 200mb (39,000 ft):

http://home.houston.rr.com/wx/isabel42.gif

And here's one for the mid levels (500mb = 18,000 ft)

http://home.houston.rr.com/wx/isabel43.gif

Note at 500 mb that Isabel is nearing the SW periphery of the ridge. Also note the position of the ridge over Florida and mid to upper level winds coming from west to east across Florida. That's good news for Florida. Isabel is approaching the weakness in the ridge. But I would caution you that even though the models are in excellent agreement, just a slightly more west course could yet threaten SC or NC.

[mike01205]

why a High Pressure where Isabel is?

[Deenac813]

Thanks wxman for the link.. I am new at this but beginning to see the turn everyone is talking about.... Please let me know if I am thinking right.. Isabel cannot go thru the high over Florida right?? she will take the path basically were the low is??

[Stormsfury]

A high pressure at the 200mb level is the anticyclone that is venting Isabel.

[Superstorm]

Because of the anticyclone over the hurricane?

[wxman57]

Good question, Mike. Rmember, you're looking at the TOP of the hurricane on that 200mb (39,000ft) chart. At the surface, hurricanes spin cyclonically (counter-clockwise in the northern hemisphere), and pressure is lowest. Winds are streaming in toward Isabel's eye at almost 200 mph, and that air has to go up. But aloft, all that rising warm air would be trapped in the storm without a good exhause mechanism - i.e., a high pressure center. In high pressure centers, winds blow outward from the center in a clockwise direction. All well-developed hurricanes have a high center overhead. The high helps to spread the rising air out in all quadrants of the top of the storm.

Here are a few web sites with hurricane structure info:

http://www.comet.ucar.edu/nsflab/web/hurricane/321.htm

Here's an even better site:
http://www.planearthsci.com/products/Hu ... truct.html

[mike01205]

thank you wxman57 that makes alot of sense