WDIO32 PGTW 240900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 06B (HAMOON) WARNING 
NR 005//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 20.4N 90.4E
   INITIAL INTENSITY: 80 KTS
   GEOGRAPHIC REFERENCE: 138 NM SOUTHWEST OF CHITTAGONG
   MOVEMENT PAST 6 HOURS: EAST-NORTHEASTWARD AT 13 KTS
   SIGNIFICANT WAVE HEIGHT: 33 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
TROPICAL CYCLONE (TC) 06B (HAMOON) HAS REACHED PEAK INTENSITY AND
WILL NOW BEGIN TO WEAKEN AS IT APPROACHES THE COAST OF MYANMAR.
EARLIER ENHANCED INFRARED IMAGERY (EIR) SHOWS THAT THE SYSTEM
DEVELOPED A PINHOLE EYE FEATURE AROUND 0000Z, WHICH WAS RELATIVELY
SHORT-LIVED, FILLING IN COMPLETELY BY 0500Z. A 240001Z GMI PASS
REVEALED A WELL-DEFINED MICROWAVE EYE FEATURE IN BOTH THE 37GHZ AND
89GHZ BANDS BUT UNFORTUNATELY THAT IS THE LAST MICROWAVE IMAGE
AVAILABLE FOR THIS SYSTEM. THUS THE INITIAL POSITION IS ASSESSED
WITH MEDIUM CONFIDENCE USING THE ANIMATED MULTISPECTRAL SATELLITE
IMAGERY (MSI) FROM BOTH METEOSAT-9 AND HIMAWARI-9. THE INITIAL
INTENSITY IS SET AT 80 KNOTS WITH MEDIUM CONFIDENCE. REANALYSIS OF
THE 0000Z POSITION RESULTED IN AN INCREASE OF THE INITIAL INTENSITY
AT 0000Z TO 80 KNOTS, AND THUS THERE IS NO CHANGE TO THE INITIAL
INTENSITY AT 0600Z. THE INITIAL INTENSITY IS SUPPORTED BY THE
AGENCY FIXES BETWEEN T4.0 AND T5.0, AS WELL AS THE CIMSS ADT. THE
SYSTEM HAS PICKED UP SPEED OVER THE PAST 12 HOURS AND IS NOW
TRACKING EAST-NORTHEAST AT 13 KNOTS, ALONG THE WESTERN SIDE OF A
DEEP-LAYER SUBTROPICAL RIDGE (STR) CENTERED NEAR HONG KONG.
CONDITIONS ARE NOT FAVORABLE FOR ADDITIONAL DEVELOPMENT, WITH THE
SYSTEM NOW UNDER A REGION OF HIGH WESTERLY WIND SHEAR, OFFSET
SOMEWHAT BY EXTREMELY STRONG POLEWARD OUTFLOW AND VERY WARM SSTS.
THE CIRA ADVECTED LAYER PRECIPITABLE WATER PRODUCT REVEALS VERY LOW
MOISTURE VALUES ABOVE 500MB AND ONLY MODERATE LEVELS ABOVE 700MB,
INDICATING THE SYSTEM IS ALREADY SHALLOWING OUT.

INITIAL WIND RADII BASIS: SCATTEROMETER DATA 

CURRENT STEERING MECHANISM: WESTERN PERIPHERY OF A DEEP-LAYER
SUBTROPICAL RIDGE (STR) CENTERED NEAR HONG KONG.

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T4.5 - 77 KTS
   KNES: T5.0 - 90 KTS
   DEMS: T4.0 - 65 KTS
   CIMSS SATCON: 87 KTS AT 240300Z
   CIMSS ADT: 77 KTS AT 240530Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY
UNFAVORABLE
   VWS: 25-30 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: STRONG POLEWARD
   OTHER FACTORS: EXTREMELY DRY AIR ABOVE 500MB. 

ANALYSIS CONFIDENCE:
   INITIAL POSITION: MEDIUM
   INITIAL INTENSITY: MEDIUM
   INITIAL WIND RADII: HIGH

3. FORECAST REASONING.

SIGNIFICANT FORECAST CHANGES: THERE ARE NO SIGNIFICANT CHANGES TO
THE FORECAST FROM THE PREVIOUS WARNING.

FORECAST DISCUSSION: TC 06B (HAMOON) WILL CONTINUE TRACKING TOWARDS
THE EAST-NORTHEAST THROUGH THE NEXT 12 TO 18 HOURS ALONG THE
WESTERN SIDE OF THE STEERING RIDGE TO THE EAST. TRACK SPEEDS ARE
EXPECTED TO SLOW DOWN A BIT OVER THE NEXT 12 HOURS AS THE STEERING
GRADIENT IS ANTICIPATED TO WEAKEN SLIGHTLY. LANDFALL IS CURRENTLY
EXPECTED IN THE VICINITY OF COXS BAZAAR AROUND THE 1800Z HOUR,
HOWEVER, IT REMAINS POSSIBLE THAT THE SYSTEM KEEPS UP ITS CURRENT
SPEED OF ADVANCE, WHICH WOULD RESULT IN AN EARLIER LANDFALL. IN
TERMS OF INTENSITY, AS DISCUSSED ABOVE, THE SYSTEM HAS ALREADY
REACHED ITS PEAK INTENSITY AND IS NOW ON THE DECLINE. DEEP-LAYER
SHEAR VALUES ALREADY EXCEED 30 KNOTS, WITH THE HIGH-RESOLUTION
MODELS SUGGESTING EVEN HIGHER MID-LEVEL SHEAR. ADDITIONALLY, THE
PRESENCE OF A VERY DRY MID- TO UPPER-LEVEL AIR MASS WHICH IS
ALREADY MOVING IN FROM THE WEST, WILL SERVE TO BOTH DECOUPLE THE
VORTEX AND SMOTHER ANY DEEP CONVECTION THAT MANAGES TO FORM. THIS
COMBINATION WILL LEAD TO A WEAKENING TREND FROM NOW THROUGH
LANDFALL. HOWEVER, THE WIND FIELD WILL TAKE SOME TIME TO SPIN DOWN,
AND THUS THE SYSTEM IS EXPECTED TO MAKE LANDFALL AS A 70 KNOT
TROPICAL CYCLONE. AFTER LANDFALL, THE RUGGED TERRAIN ALONG THE
INDIA-MYANMAR BORDER WILL TEAR THE REMNANT VORTEX APART AS IT
TRACKS TOWARDS THE NORTHEAST. FULL DISSIPATION IS EXPECTED NO LATER
THAN TAU 48. 

MODEL DISCUSSION: TRACK GUIDANCE IS IN GOOD CROSS-TRACK SPREAD
THROUGH THE ENTIRETY OF THE SHORT FORECAST PERIOD. ALONG-TRACK
SPREAD PICKS UP EVEN AS EARLY AS TAU 12, AS THE MODELS ARE
STRUGGLING WITH THE SPEED OF THIS SYSTEM AS IT TRACKS TOWARDS THE
COAST. THE GFS AND NAVGEM ARE THE PACK LEADERS, WHILE THE REMAINDER
OF THE GUIDANCE LAGS BEHIND, SHOWING THE SYSTEM REMAINING OFFSHORE
BY TAU 12. ALONG-TRACK SPREAD INCREASES FURTHER AS THE SYSTEM MOVES
INLAND IN THE LATER PORTION OF THE FORECAST. THE JTWC TRACK LIES
CLOSE TO THE CONSENSUS MEAN THROUGH THE FORECAST PERIOD, WITH
MEDIUM CONFIDENCE. INTENSITY GUIDANCE IS IN GOOD AGREEMENT THAT THE
SYSTEM WILL WEAKEN SLIGHTLY PRIOR TO LANDFALL, WITH THE BULK OF THE
GUIDANCE SHOWING A 60-70 KNOT SYSTEM AT TAU 12. ALL AVAILABLE
GUIDANCE SHOWS A RAPID WEAKENING AFTER LANDFALL WITH DISSIPATION
BETWEEN TAU 36 AND TAU 48. 

FORECAST CONFIDENCE:
   TRACK 0 - 72 HR: MEDIUM
   INTENSITY 0 - 72 HR: MEDIUM//
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