WDPN31 PGTW 220900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 04W (PRAPIROON) WARNING 
NR 011//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 20.1N 108.7E
   INITIAL INTENSITY: 55 KTS
   GEOGRAPHIC REFERENCE: 166 NM EAST-SOUTHEAST OF HANOI, VIETNAM
   MOVEMENT PAST 6 HOURS: NORTHWESTWARD AT 07 KTS
   SIGNIFICANT WAVE HEIGHT: 18 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS TROPICAL
STORM 04W (PRAPIROON) AS HAVING A WELL-DEFINED AND SYMMETRIC CDO
OVER THE CENTER OF THE OBSCURED LOW-LEVEL CIRCULATION CENTER
(LLCC). ENVIRONMENTAL ANALYSIS INDICATES THAT 04W IS CURRENTLY IN A
FAVORABLE ENVIRONMENT FOR INTENSIFICATION CHARACTERIZED BY MODERATE
RADIAL OUTFLOW ALOFT, LOW VERTICAL WIND SHEAR, AND VERY WARM (30-31
C) SEA SURFACE TEMPERATURES. HOWEVER, AS 04W APPROACHES LAND, THE
ENVIRONMENT WILL VERY RAPIDLY WORSEN. THE INITIAL POSITION IS
PLACED WITH HIGH CONFIDENCE BASED ON A 220518Z GMI 37 GHZ MICROWAVE
IMAGE SHOWING A DEFINED MICROWAVE EYE FEATURE. THE INITIAL
INTENSITY OF 55 KTS IS ASSESSED WITH MEDIUM CONFIDENCE BASED ON THE
OBJECTIVE AND SUBJECTIVE INTENSITY ESTIMATES LISTED BELOW.

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
   KNES: T3.5 - 55 KTS
   CIMSS SATCON: 62 KTS AT 220600ZZ
   CIMSS ADT: 55 KTS AT 220600ZZ
   CIMSS DPRINT: 48 KTS AT 220600Z
   CIMSS DMINT: 49 KTS AT 220539Z
   CIMSS MW SOUNDERS: 65 KTS AT 220629Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 10-15 KTS
   SST: 30-31 CELSIUS
   OUTFLOW: MODERATE RADIAL

ANALYSIS CONFIDENCE:
   INITIAL POSITION: HIGH
   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: TS 04W IS FORECAST TO CONTINUE TRACKING ALONG
THE SOUTHWESTERN PERIPHERY OF THE STR FOR THE REMAINDER OF THE
FORECAST PERIOD. LANDFALL IS FORECAST TO OCCUR BETWEEN TAU 12 AND
24 ABOUT 100 NM EAST OF HANOI, VIETNAM. AFTER MAKING LANDFALL 04W
IS EXPECTED TO QUICKLY WEAKEN, AND AROUND TAU 36, MAKE A
SOUTHWESTWARD TURN AS THE LOWER-LEVEL STEERING PATTERN COMES INTO
EFFECT, WITH DISSIPATION FORECAST TO OCCUR NEAR TAU 48. THE CURRENT
55 KNOT INTENSITY IS FORECAST TO CONTINUE FOR THE NEXT 12 HOURS AS
THE VERY WARM AND HIGH OHC PROVIDE AMPLE ENERGY TO THE SYSTEM. IF
THE TRACK SPEED SLOWS TOO MUCH, THERE MAY BE ENOUGH TIME FOR
FURTHER INTENSIFICATION, BUT IF TRACK SPEEDS ARE MAINTAINED THEN
THERE WILL NOT BE ENOUGH TIME FOR THE SYSTEM TO TAP INTO THE
AVAILABLE ENERGY OF THE ENVIRONMENT BEFORE MAKING LANDFALL. 

MODEL DISCUSSION: NUMERICAL MODEL GUIDANCE IS IN VERY GOOD
AGREEMENT IN THE NEAR TERM WITH A 60 NM CROSS-TRACK SPREAD AT TAU
24. MANY MODELS BECOME ERRATIC AFTERWARDS THOUGH AS THE VORTEX
WEAKENS, BUT MOST CALL FOR A WESTWARD TURN WITH VARYING DEGREES.
OVERALL, THE JTWC TRACK FORECAST IS PLACED WITH HIGH CONFIDENCE.
THE INTENSITY GUIDANCE IS ALSO IN GOOD AGREEMENT, WITH THE
EXCEPTION OF HWRF, WHICH HAS A PEAK INTENSITY OF 70 KTS AT TAU 12.
THE REST OF CONSENSUS EITHER STARTS A WEAKENING TREND OR MAINTAINS
THE 55 KNOT INTENSITY AS 04W CROSSES THE GULF OF TONKIN. THE JTWC
INTENSITY FORECAST IS PLACED WITH MEDIUM CONFIDENCE DUE IN PART TO
THE POSSIBILITY OF INTENSIFICATION IF TRACK SPEEDS SLOW TOO MUCH. 

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