WDPN31 PGTW 251500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 22W (TRAMI) WARNING NR 
021//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 17.6N 115.9E
   INITIAL INTENSITY: 55 KTS
   GEOGRAPHIC REFERENCE: 298 NM SOUTH-SOUTHEAST OF HONG KONG
   MOVEMENT PAST 6 HOURS: WESTWARD AT 11 KTS
   SIGNIFICANT WAVE HEIGHT: 22 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS AN
ASYMMETRIC SYSTEM, WITH THE NORTHERN SIDE RELATIVELY CLEAR OF
SIGNIFICANT CONVECTION, WHILE TO THE SOUTH LIES AN IMPRESSIVE
CONVECTIVE MASS, WITH CLOUD TOPS COLDER THAN -91C. A 250946Z
SSMIS 37GHZ MICROWAVE IMAGE REVEALED A BROAD CENTER OUTLINED BY A
LARGE LOW EMISSIVITY REGION (LER) WITH SHALLOW BANDING FEATURES TO
THE EAST AND NORTH AND MORE ROBUST BANDING FEATURES TO THE WEST AND
SOUTH. THE INITIAL POSITION WAS PLACED ON THE NORTHERN EDGE OF THE
CONVECTION USING EXTRAPOLATION OF THE LER SEEN IN THE MICROWAVE
IMAGERY. THE INITIAL INTENSITY REMAINS SET AT 55 KNOTS, CONSISTENT
WITH THE PGTW DVORAK CURRENT INTENSITY ESTIMATE AND THE AIDT,
DPRINT AND SATCON VALUES NOTED BELOW. THE SYSTEM CONTINUES TO
STRUGGLE AGAINST PERSISTENTLY HIGH (25-30 KNOTS) EASTERLY SHEAR
AND CONTINUES TO WIN THAT BATTLE, AS EVIDENCED BY THE IMPRESSIVE
TRANSVERSE BANDING SEEN TO THE EAST OF THE SYSTEM. HOWEVER, THE
DEEP CONVECTION IS FAILING TO WRAP UPSHEAR AT THE PRESENT TIME.
WITH THE EXCEPTION OF THE SHEAR, AND SOME DRY MID-LEVEL AIR TO THE
NORTHEAST, THE ENVIRONMENT REMAINS GENERALLY FAVORABLE WITH WARM
SSTS AND STRONG EQUATORWARD OUTFLOW.

INITIAL WIND RADII BASIS: PERSISTENCE 

CURRENT STEERING MECHANISM: SOUTHERN SIDE OF A SUBTROPICAL RIDGE
(STR) COMPLEX EXTENDING FROM MYANMAR TO SOUTHEAST OF HONSHU. 

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T3.5 - 55 KTS
   RJTD: T3.0 - 45 KTS
   KNES: T3.0 - 45 KTS
   CIMSS SATCON: 58 KTS AT 251124Z
   CIMSS ADT: 41 KTS AT 251130Z
   CIMSS AIDT: 56 KTS AT 251230Z 
   CIMSS DPRINT: 57 KTS AT 251210Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY FAVORABLE
   VWS: 25-30 KTS
   SST: 28-29 CELSIUS
   OUTFLOW: STRONG EQUATORWARD
   OTHER FACTORS: DRY MID-LEVEL AIR TO THE NORTHEAST.

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

3. FORECAST REASONING.

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

FORECAST DISCUSSION: TROPICAL STORM (TS) 22W (TRAMI) IS FORECAST TO
TRACK WESTWARD ALONG THE SOUTHERN SIDE OF THE EXTENSIVE RIDGE
COMPLEX OVER THE FIRST 24 HOURS OF THE FORECAST. NO SIGNIFICANT
CHANGES TO THE INTENSITY ARE EXPECTED AS THE FAVORABLE SSTS AND
OUTFLOW CONDITIONS ARE OFFSET BY PERSISTENT MODERATE TO HIGH
EASTERLY SHEAR AND INCREASING DRY AIR FLOWING INTO THE EASTERN
HEMISPHERE OF THE CIRCULATION. BY TAU 24, SHEAR IS EXPECTED TO
INCREASE EVEN MORE, AND USHER IN WITH IT AN INFLUX OF VERY DRY
MID-LEVEL AIR WHICH WILL INHIBIT DEEP CONVECTIVE ACTIVITY, 
PARTICULARLY
IN THE EASTERN PORTION OF THE CIRCULATION. LACKING STRONG UPSHEAR
CONVECTION, THE SYSTEM WILL SUCCUMB TO THE INFLUX OF DRY AIR AND
CAP THE VORTEX IN THE MID-LEVELS, MARKING THE START OF A WEAKENING
TREND AFTER TAU 24. THE SYSTEM IS FORECAST TO BEGIN TURNING
SOUTHWESTWARD AFTER TAU 36 AS THE VORTEX SHALLOWS OUT AND THE
SYSTEM COMES UNDER THE INFLUENCE OF LOW-LEVEL NORTHERLY FLOW
FLOWING OUT OF CHINA. THE CURRENT FORECAST DOES NOT ANTICIPATE A
LANDFALL ON THE COAST OF CENTRAL VIETNAM, BUT MULTIPLE MODELS SHOW
THE SYSTEM MOVING INLAND NEAR HUE CITY OR DA NANG, VIETNAM AND A
LANDFALL CANNOT BE RULED OUT. LANDFALL OR NOT, THE SYSTEM WILL
CONTINUE TO RAPIDLY WEAKEN AS IT APPROACHES THE COASTLINE, WITH THE
WEAKENING BEING ACCELERATED IF IT DOES MOVE INLAND. A SHARP TURN TO
THE EAST IS FORECAST BY TAU 72 AS THE NOW MUCH WEAKENED VORTEX
COMES UNDER THE INFLUENCE OF A SURGE IN THE LOW-LEVEL SOUTHWESTERLY
MONSOONAL FLOW AND IS PULLED TOWARDS WHAT WILL BE TYPHOON 23W IN
THE PHILIPPINE SEA AT THAT TIME. THE SYSTEM WILL CONTINUE TRACKING
EASTWARD INTO THE CENTRAL SOUTH CHINA SEA WHILE CONTINUING TO
WEAKEN THROUGH THE END OF THE FORECAST PERIOD. IF THE SYSTEM MAKES
LANDFALL, IT WILL LIKELY DISSIPATE WELL BEFORE TAU 120. 

MODEL DISCUSSION: TRACK GUIDANCE REMAINS IN GOOD AGREEMENT ON THE
OVERALL SCENARIO, AND THE OUTLIERS (GFS AND GEFS) HAVE MOVED CLOSER
TO THE MULTI-MODEL CONSENSUS MEAN SINCE THE LAST RUN. GFS REMAINS
ON THE NORTHERN SIDE OF THE GUIDANCE ENVELOPE AND REMAINS THE ONLY
MODEL SHOWING A LANDFALL IN CENTRAL VIETNAM, THOUGH THE ECMWF IS
GETTING CLOSER TO THE COAST WITH EACH RUN. THE JTWC FORECAST IS
PLACED CLOSE TO THE CONSENSUS MEAN WITH MEDIUM TO LOW CONFIDENCE.
INTENSITY GUIDANCE IS IN GOOD AGREEMENT THAT THE SYSTEM WILL
MAINTAIN A FLAT INTENSITY OR SLIGHTLY WEAKEN IN THE FIRST 24 HOURS,
FOLLOWED BY A GENERAL WEAKENING TO TAU 48 AND A MORE RAPID
WEAKENING THEREAFTER. THE JTWC FORECAST LIES ABOUT 5 KNOTS ABOVE
THE CONSENSUS MEAN THROUGH THE FORECAST PERIOD WITH MEDIUM
CONFIDENCE. 

FORECAST CONFIDENCE:
   TRACK 0 - 72 HR: MEDIUM
   TRACK 72-120 HR: MEDIUM
   INTENSITY 0 - 72 HR: MEDIUM
   INTENSITY 72-120 HR: MEDIUM//
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