[Tropical] Tropical Cyclone Discussion

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WTNT42 KNHC 300301
TCDAT2
HURRICANE GUSTAV DISCUSSION NUMBER  21
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   AL072008
1100 PM EDT FRI AUG 29 2008

REPORTS FROM AIR FORCE RESERVE AND NOAA HURRICANE HUNTER AIRCRAFT
SHOW THAT GUSTAV HAS A 25 NM WIDE EYE THAT IS BECOMING BETTER
DEFINED IN RECENT SATELLITE IMAGERY.  RECENT TRMM AND SSM/I IMAGERY
ALONG WITH CUBAN RADAR DATA SUGGESTS THAT AN OUTER EYEWALL WITH A
DIAMETER OF ABOUT 100 N MI IS FORMING...AND THE NOAA PLANE REPORTED
88 KT FLIGHT-LEVEL WINDS AT 770 MB IN THE CORRESPONDING OUTER WIND
MAXIMUM.  RELIABLE-LOOKING DATA FROM THE SFMR SHOWS 65-70 KT
SURFACE WINDS IN BOTH THE INNER AND OUTER WIND MAXIMA...BUT THE
HURRICANE FORCE WINDS ARE CURRENTLY CONFINED TO THE NORTHEASTERN
QUADRANT.  THE INITIAL INTENSITY IS SET TO 70 KT IN AGREEMENT WITH
THE AIRCRAFT DATA.

THE INITIAL MOTION IS 305/9.  THERE IS NO CHANGE TO THE FORECAST
PHILOSOPHY FROM THE PREVIOUS PACKAGE...WITH GUSTAV EXPECTED TO MOVE
GENERALLY NORTHWESTWARD ON THE SOUTHWEST SIDE OF A LOW/MID-LEVEL
RIDGE OVER THE EASTERN UNITED STATES.  THERE HAS ALSO BEEN LITTLE
CHANGE IN THE GUIDANCE...WITH SOME CONTINUING DISAGREEMENT ON HOW
MUCH RIDGING WILL EXTEND WESTWARD TO THE NORTH OF GUSTAV AND HOW
GUSTAV WILL INTERACT WITH AN UPPER-LEVEL TROUGH OVER THE GULF OF
MEXICO.  THE GUIDANCE IS TIGHTLY CLUSTERED THROUGH 48 HR AND THEN
SHOWS SOME SPREAD.  THE GFDL REMAINS ON THE EASTERN SIDE OF THE
GUIDANCE ENVELOPE AND CALLS FOR LANDFALL IN SOUTHEASTERN
LOUISIANA...WHILE THE UKMET CALLS FOR A WESTWARD TURN AND LANDFALL
ON THE MIDDLE TO UPPER TEXAS COAST.  THE REMAINDER OF THE GUIDANCE
LIES BETWEEN THESE EXTREMES.  THE NEW FORECAST TRACK IS AN UPDATE
OF THE PREVIOUS FORECAST FOR THE FIRST 72 HR...THEN IS SLOWER AND A
LITTLE TO THE LEFT OF THE PREVIOUS FORECAST THEREAFTER.  IT LIES IN
THE EASTERN SIDE OF THE GUIDANCE ENVELOPE.

THE INTENSITY FORECAST REMAINS PROBLEMATIC.  WHILE GUSTAV HAS GOOD
OUTFLOW IN ALL QUADRANTS...WATER VAPOR IMAGERY SUGGESTS WESTERLY
FLOW ASSOCIATED WITH THE GULF OF MEXICO TROUGH UNDERCUTTING THE
OUTFLOW.  THIS...COMBINED WITH THE CONCENTRIC WIND MAXIMA...MAY BE
SLOWING INTENSIFICATION.  GUSTAV IS OVER WARM WATER WITH HIGH
OCEANIC HEAT CONTENT...AND SHOULD REMAIN OVER SUCH WATER UNTIL IS
PASSES NORTH OF THE LOOP CURRENT IN 48-60 HR.  THUS...THERE IS A
DISTINCT POSSIBILITY OF RAPID INTENSIFICATION IF THE STORM
STRUCTURE AND THE INTERACTION WITH THE TROUGH PERMIT.  THE SHIPS
MODEL CALLS FOR A PEAK INTENSITY OF 104 KT...THE LGEM 97 KT...THE
HWRF 114 KT...THE FLORIDA STATE SUPERENSEMBLE 114 KT...AND THE GFDL
129 KT.  BASED ON THIS AND THE PREMISE THAT THE INTERACTION WITH
THE TROUGH WILL ALLOW STEADY STRENGTHENING...THE FORECAST PEAK
INTENSITY IS INCREASED TO 115 KT.  GUSTAV COULD GET STRONGER THAN
THAT IF RAPID INTENSIFICATION OCCURS.  THE INTENSITY FORECAST SHOWS
A SLIGHT WEAKENING AT 72 HR AS GUSTAV REACHES LOWER OCEANIC HEAT
CONTENT AND POSSIBLE ENCOUNTERS SOME WESTERLY SHEAR.  HOWEVER...
GUSTAV IS EXPECTED TO MAKE LANDFALL AS A MAJOR HURRICANE.  THE
FINAL FLY IN THE OINTMENT IS THE POSSIBILITY OF EYEWALL REPLACEMENT
CYCLES... WHICH COULD SIGNIFICANTLY AFFECT THE INTENSITY.

FORECAST POSITIONS AND MAX WINDS

INITIAL      30/0300Z 19.5N  80.4W    70 KT
 12HR VT     30/1200Z 20.6N  81.8W    85 KT
 24HR VT     31/0000Z 22.3N  83.7W   100 KT...INLAND
 36HR VT     31/1200Z 24.0N  85.6W   105 KT
 48HR VT     01/0000Z 25.7N  87.6W   115 KT
 72HR VT     02/0000Z 28.5N  90.5W   110 KT
 96HR VT     03/0000Z 30.5N  93.0W    80 KT...INLAND
120HR VT     04/0000Z 31.5N  94.0W    45 KT...INLAND

$$
FORECASTER BEVEN



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