Hurricane GUSTAV

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HURRICANE GUSTAV DISCUSSION NUMBER  31
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   AL072008
500 AM EDT MON SEP 01 2008
 
OBSERVATIONS FROM AN AIR FORCE HURRICANE HUNTER AIRCRAFT INDICATE
THAT GUSTAV IS NOT STRENGTHENING.  THE CENTRAL PRESSURE HAS RISEN
SLIGHTLY AND...BASED ON RECENT FLIGHT-LEVEL AND SFMR SURFACE WIND
MEASUREMENTS...100 KT IS A GENEROUS ESTIMATE FOR THE CURRENT
INTENSITY.  WSR-88D RADAR IMAGES SHOW THAT THE EYE WALL IS OPEN
OVER THE SOUTHERN SEMICIRCLE...PERHAPS DUE TO THE MID- TO
UPPER-LEVEL DRY AIR INTRUSION FROM THE SOUTH THAT WAS DISCUSSED
EARLIER.  IN FACT...THE AIR FORCE HURRICANE HUNTERS DID NOT REPORT
AN EYEWALL.  WATER VAPOR IMAGERY ALSO SUGGESTS A DRY INTRUSION AND
A RESTRICTION OF THE UPPER-LEVEL OUTFLOW OVER THE SOUTHERN PORTION
OF THE HURRICANE.  ALSO THE CLOUD PATTERN HAS BECOME A BIT MORE
RAGGED ON GEOSTATIONARY SATELLITE PICTURES.  BASED ON CURRENT
TRENDS AND THE PROXIMITY TO THE COAST...NO SIGNIFICANT INCREASE IN
STRENGTH APPEARS LIKELY PRIOR TO LANDFALL.
 
GUSTAV CONTINUES MOVING BRISKLY TOWARD THE NORTHWEST...315/14. THE
HURRICANE CONTINUES TO BE STEERED BY THE FLOW TO THE SOUTH AND
SOUTHWEST OF A MID-TROPOSPHERIC ANTICYCLONE/HIGH OVER THE EASTERN
UNITED STATES.  GLOBAL MODELS SHOW THE HIGH WEAKENING OVER THE NEXT
DAY OR SO AND THEREFORE GUSTAV'S FORWARD SPEED IS LIKELY TO SLOW
LATER TODAY AND TOMORROW...I.E. AFTER THE SYSTEM HAS MOVED INLAND.
THE STEERING PATTERN BECOMES ILL-DEFINED LATER IN THE FORECAST
PERIOD AND THE TRACK MODELS BECOME HIGHLY DIVERGENT.  IF GUSTAV
REMAINED A VERTICALLY-COHERENT CYCLONE IT WOULD PROBABLY RESPOND TO
AN INCREASING SOUTHWESTERLY UPPER-LEVEL FLOW AS FORECAST BY THE
GLOBAL MODELS.  HOWEVER IT IS QUITE POSSIBLE THAT THE UPPER-LEVEL
PART OF GUSTAV WILL BE SHEARED OFF TO THE NORTHEAST...LEAVING THE
LOW-LEVEL CIRCULATION BEHIND IN THE EAST TEXAS AREA.  THAT IS
BASICALLY WHAT WE ARE INDICATING IN THIS OFFICIAL TRACK FORECAST
WHICH SHOWS GUSTAV OR ITS REMNANTS SLOWING TO A CRAWL IN DAYS 3 TO
5.  SUCH SLOW MOTION WOULD EXACERBATE THE THREAT OF HEAVY RAINS AND
INLAND FLOODING.
 
 
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      01/0900Z 28.4N  89.5W   100 KT
 12HR VT     01/1800Z 29.5N  91.1W   100 KT...INLAND
 24HR VT     02/0600Z 30.7N  92.8W    55 KT...INLAND
 36HR VT     02/1800Z 31.4N  93.9W    35 KT...INLAND
 48HR VT     03/0600Z 31.8N  94.7W    25 KT...INLAND
 72HR VT     04/0600Z 32.0N  95.5W    20 KT...INLAND
 96HR VT     05/0600Z 32.0N  96.0W    20 KT...INLAND
120HR VT     06/0600Z 32.0N  96.5W    20 KT...REMNANT LOW
 
$$
FORECASTER PASCH
 
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