WDPN31 PGTW 220300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 04W (PRAPIROON) WARNING 
NR 010//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 19.6N 109.2E
   INITIAL INTENSITY: 45 KTS
   GEOGRAPHIC REFERENCE: 204 NM EAST-SOUTHEAST OF HANOI, VIETNAM
   MOVEMENT PAST 6 HOURS: NORTHWESTWARD AT 12 KTS
   SIGNIFICANT WAVE HEIGHT: 15 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
TROPICAL STORM (TS) 04W (PRAPIROON) CLEARLY DID NOT GET THE MEMO
ABOUT TROPICAL CYCLONES WEAKENING OVER LAND. AFTER MAKING LANDFALL
PRIOR TO 1800Z, THE SYSTEM RAPIDLY TRAVERSED OVER CENTRAL HAINAN,
MAINTAINING A WELL-DEFINED RADAR EYE AND ACTUALLY IMPROVING IN THE
MICROWAVE DEPICTION. ANIMATED MULTISPECTRAL SATELLITE IMAGERY
(MSI), AND RADAR DATA INDICATE THE LOW LEVEL CIRCULATION CENTER
(LLCC) WAS RIGHT ALONG THE NORTHWEST COAST OF HAINAN AT 0000Z AND
IS ALREADY MOVING OFFSHORE AT A BRISK CLIP. ANALYSIS OF THE MSI,
THE LATEST MICROWAVE IMAGE FROM 2245Z AND THE MOST RECENT RADAR
DATA SUGGESTS THAT THERE MAY BE A BIT OF SOUTHEASTERLY SHEAR
CAUSING SOME VORTEX TILT TO THE NORTHWEST AND A BIT OF SEPARATION
BETWEEN THE TIGHT SWIRL IN THE VISIBLE IMAGERY VERSUS THE RADAR EYE
FEATURE. USING THE RADAR EYE AS GROUND TRUTH, THE INITIAL POSITION
IS ASSESSED WITH HIGH CONFIDENCE. THE INITIAL INTENSITY OF 45 KNOTS
IS ASSESSED WITH MEDIUM CONFIDENCE, BASED ON AVAILABLE AGENCY FIXES
NOTED BELOW, THE DPRINT OF 47 KNOTS. CIMSS ATMOSPHERIC MOTION
VECTORS (AMVS) SUGGEST THE DEVELOPMENT OF A MESOSCALE POINT SOURCE
OVER TOP OF THE SYSTEM AS IT MOVED ACROSS HAINAN, RESULTING A SMALL
BUBBLE OF LOWER SHEAR VALUES. NOW THAT THE SYSTEM IS BACK OVER
WATER, THE ENVIRONMENT IS FAVORABLE FOR INTENSIFICATION, WITH VERY
WARM (30-31C), VERY HIGH OHC (EXCEEDING 110 KJ PER CM2) AND GOOD
WESTWARD AND EQUATORWARD OUTFLOW.

INITIAL WIND RADII BASIS: PERSISTENCE 

CURRENT STEERING MECHANISM: SOUTHWEST PERIPHERY OF A DEEP-LAYER
SUBTROPICAL RIDGE (STR) TO THE NORTHEAST. 

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T3.0 - 45 KTS
   RJTD: T3.0 - 45 KTS
   RCTP: T2.5 - 35 KTS

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 5-10 KTS
   SST: 30-31 CELSIUS
   OUTFLOW: MODERATE EQUATORWARD

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

3. FORECAST REASONING.

SIGNIFICANT FORECAST CHANGES: THERE ARE NO MAJOR CHANGES TO THE
TRACK. HOWEVER, DUE TO THE SYSTEM MAINTAINING A WELL-DEFINED
STRUCTURE DURING ITS TRAVERSE OVER LAND, THE INTENSITY FORECAST HAS
BEEN CHANGED FROM WEAKENING IN THE GULF OF TONKIN TO
INTENSIFICATION. 

FORECAST DISCUSSION: TS 04W HAS IS NOW MOVING BACK OVER THE ZESTY
WATERS OF THE GULF OF TONKIN. THE SYSTEM IS FORECAST TO CONTINUE
TRACKING NORTHWESTWARD AT A BRISK SPEED FOR THE NEXT 12 HOURS
BEFORE BEGINNING TO SLOW DOWN SHARPLY AS IT APPROACHES THE FAR
NORTHEASTERN COAST OF VIETNAM. LANDFALL IN THE VICINITY OF CAM PHA,
VIETNAM IS ANTICIPATED WITHIN THE NEXT 12-18 HOURS. ONCE A BIT
FURTHER AWAY FROM THE COAST OF HAINAN, THE SYSTEM WILL MOVE INTO A
VERY FAVORABLE OCEAN ENVIRONMENT, WITH A HUGE AMOUNT OF POTENTIAL
ENERGY TO TAP INTO. IF THE TRACK SPEED MAINTAINS ITS CURRENT PACE,
THEN INTENSIFICATION WILL BE SOMEWHAT LIMITED, TO AROUND 55 KNOTS.
HOWEVER, IF THE SLOW DOWN STARTS EARLIER THAN EXPECTED, PEAK
INTENSITIES COULD APPROACH TYPHOON STRENGTH BEFORE LANDFALL. SHEAR
VALUES ARE EXPECTED TO REMAIN LOW FOR THE NEXT 18 HOURS AND WILL
PICK UP AS THE SYSTEM IS MAKING LANDFALL. AFTER LANDFALL, THE
COMBINATION OF TERRAIN INTERACTION AND INCREASED SHEAR WILL TEAR
THE SYSTEM APART, WITH THE REMNANT VORTEX TURNING WEST AS IT
DISSIPATES, AND EVENTUALLY TO THE SOUTH AFTER DISSIPATION BELOW
WARNING CRITERIA. 

MODEL DISCUSSION: TRACK GUIDANCE IS IN GOOD AGREEMENT THROUGH THE
DURATION OF THE FORECAST PERIOD, WITH A SPREAD OF JUST 40NM AT
LANDFALL, LENDING HIGH CONFIDENCE TO THE JTWC TRACK FORECAST.
INTENSITY GUIDANCE IS MIXED, WITH HWRF SHOWING NO FURTHER
INTENSIFICATION, WHILE THE REMAINDER OF THE GUIDANCE IS BETWEEN
THAT AND THE HAFS-A WHICH PEAKS THE SYSTEM AT 55 KNOTS IS 12 HOURS.
THE JTWC FORECAST FOLLOWS THE HAFS-A, BUT AS MENTIONED BEFORE,
THERE IS A NON-ZERO CHANCE OF A PERIOD OF RAPID INTENSIFICATION,
WHICH COULD SEE THE PEAK CLOSE TO TYPHOON STRENGTH. WHILE NONE OF
THE MODEL GUIDANCE SUGGESTS SUCH AN OUTCOME, THE ENVIRONMENT IS
SUPPORTIVE, AND EVERYTHING DEPENDS ON THE TRACK SPEED. 

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