[Tropical] Tropical Cyclone Discussion

[EMWIN Server]

WTNT42 KNHC 302059
TCDAT2
HURRICANE GUSTAV DISCUSSION NUMBER  25
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   AL072008
500 PM EDT SAT AUG 30 2008

THE CENTER OF THE EYE OF GUSTAV HAD BEEN HUGGING THE EASTERN COAST
OF THE ISLE OF YOUTH EARLIER THIS AFTERNOON...BUT IS NOW OVER WATER
IN BETWEEN THAT ISLAND AND MAINLAND WESTERN CUBA.  AIRCRAFT FIXES
CONTINUE TO COME IN JUST ABOUT RIGHT ALONG THE PREVIOUS FORECAST
TRACK.  VISIBLE SATELLITE IMAGERY SUGGESTS GUSTAV HAS BEEN WOBBLING
SLIGHTLY...BUT THE INITIAL MOTION APPEARS RELATIVELY
WELL-ESTABLISHED AT 315/13...WITH STEERING PROVIDED BY A MID-LEVEL
RIDGE OVER THE WESTERN ATLANTIC.  THE VARIOUS MODELS HAVE COME INTO
BETTER AGREEMENT ON A TRACK INTO THE NORTH-CENTRAL GULF COAST
WITHIN THE NEXT COUPLE OF DAYS.  THE HWRF...UKMET...AND
NOGAPS...WHICH HAD PREVIOUSLY FORECAST A STALL JUST OFFSHORE...HAVE
COME INTO THE FOLD WITH THE GFS...GFDL...AND ECMWF...RESULTING IN A
CONSENSUS TRACK THAT FALLS VERY CLOSE TO THE PATH OF THE PREVIOUS
ADVISORY.  THIS AGREEMENT HAS ALSO RESULTED...HOWEVER...IN A
CONSENSUS TRACK THAT REACHES THE COAST A LITTLE FASTER.  THE NEW
OFFICIAL TRACK IS ALMOST EXACTLY ALONG THE PATH OF THE PREVIOUS
ADVISORY...BUT MAINTAINS THE CURRENT HEADING AND SPEED ALL THE WAY
TO THE COAST...ARRIVING THERE A LITTLE SOONER THAN BEFORE.  WHILE
THERE IS INCREASED CONFIDENCE IN BOTH THE PATH AND SPEED OF THE
TRACK THROUGH ABOUT 48 HOURS...THE MODEL SPREAD IS STILL
SUFFICIENTLY LARGE TO SERVE AS A REMINDER THAT WE CANNOT SPECIFY
EXACTLY WHERE OR WHEN THE CENTER OF GUSTAV WILL MAKE FINAL
LANDFALL.  AFTER LANDFALL...ALL OF THE MODELS RESPOND TO WEAKENING
STEERING CURRENTS...WELL TO THE SOUTHWEST OF THE HIGH OVER THE
NORTHEASTERN UNITED STATES...BY FORECASTING A DRAMATIC SLOWING OF
THE FORWARD SPEED OVER LOUISIANA AND EASTERN TEXAS...AND THE
OFFICIAL FORECAST AGAIN FOLLOWS SUIT.

THE RECON CENTRAL PRESSURES HAVE CONTINUED TO STEADILY FALL...WITH
THE MOST RECENT VALUE BEING 942 MB.  A FLIGHT-LEVEL WIND OF 143 KT
AT 700 MB WAS JUST REPORTED IN THE NORTHEASTERN EYEWALL...WHICH
SUPPORTS INCREASING THE ADVISORY INTENSITY TO 130 KT.  MODEST
ADDITIONAL STRENGTHENING DURING THE NEXT FEW HOURS COULD LEAD TO
CATEGORY FIVE INTENSITY AS GUSTAV CROSSES WESTERN CUBA...BUT THE
OFFICIAL FORECAST DOES NOT EXPLICITLY CALL FOR CATEGORY FIVE STATUS
UNTIL 24 HOURS.  AFTER DEPARTING CUBA...THE HURRICANE WILL PASS
OVER THE WARM LOOP CURRENT IN THE SOUTHEASTERN GULF OF MEXICO...AND
VERTICAL WIND SHEAR IS NOT FORECAST BY THE MODELS TO BECOME
PROHIBITIVELY STRONG DURING THE NEXT COUPLE OF DAYS...SO THE
OFFICIAL FORECAST MAINTAINS A MAJOR HURRICANE ALL THE WAY TO FINAL
LANDFALL.  THIS FORECAST IS VERY CLOSE TO THE SHIPS MODEL AND ALSO
NOT TOO DIFFERENT FROM THE GFDL AND HWRF.

THE NHC WIND SPEED PROBABILITIES...INCLUDED IN THIS ADVISORY PACKAGE
IN BOTH TEXT AND GRAPHICAL FORMATS...DEPICT A RELATIVELY SIMILAR
RISK OF HURRICANE-FORCE WINDS AT INDIVIDUAL LOCATIONS ALONG A WIDE
STRETCH OF THE NORTHERN GULF COAST.  GIVEN THAT THESE VALUES ARE
SUFFICIENTLY HIGH...AND CONSIDERING THE SLIGHTLY FASTER TRACK
TOWARD THE COAST...IT IS TIME TO ISSUE HURRICANE AND TROPICAL STORM
WATCHES ALONG THE NORTHERN GULF COAST.


FORECAST POSITIONS AND MAX WINDS

INITIAL      30/2100Z 22.1N  82.9W   130 KT
 12HR VT     31/0600Z 23.4N  84.4W   135 KT
 24HR VT     31/1800Z 25.3N  86.5W   140 KT
 36HR VT     01/0600Z 27.2N  88.6W   135 KT
 48HR VT     01/1800Z 29.0N  90.7W   125 KT
 72HR VT     02/1800Z 31.0N  93.0W    70 KT...INLAND
 96HR VT     03/1800Z 32.0N  94.5W    35 KT...INLAND
120HR VT     04/1800Z 32.0N  96.0W    30 KT...INLAND

$$
FORECASTER KNABB

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