WDPN31 PGTW 190300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 09W (WIPHA) WARNING NR 
003//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 20.1N 119.8E
   INITIAL INTENSITY: 50 KTS
   GEOGRAPHIC REFERENCE: 340 NM EAST-SOUTHEAST OF HONG KONG
   MOVEMENT PAST 6 HOURS: WEST-NORTHWESTWARD AT 09 KTS
   SIGNIFICANT WAVE HEIGHT: 20 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS TROPICAL
STORM 09W (WIPHA) WITH A WELL-DEFINED, PARTIALLY EXPOSED LOW-LEVEL
CIRCULATION CENTER (LLCC) AND BROAD SWATHS OF CONVECTION WRAPPING
AROUND THE WESTERN AND SOUTHERN PERIPHERIES OF THE LLCC. AN 182202Z
WSFM 89 GHZ MICROWAVE IMAGE REVEALED THE DEFINED CONVECTIVE BAND
ALONG THE WESTERN SEMICIRCLE AND LOW-LEVEL CLOUDS TIGHTLY WRAPPING
INTO THE ASSESSED CENTER. ENVIRONMENTAL ANALYSIS INDICATES THAT 09W
IS IN A FAVORABLE ENVIRONMENT CHARACTERIZED BY STRONG EQUATORWARD
OUTFLOW ALOFT, LOW (10-15 KTS) EAST-NORTHEASTERLY VERTICAL WIND
SHEAR, AND WARM (29-30 C) SEA SURFACE TEMPERATURES. THE INITIAL
POSITION IS PLACED WITH MEDIUM CONFIDENCE BASED ON EXTRAPOLATION
FROM THE MENTIONED WSFM MICROWAVE IMAGE AND ANIMATED MSI. THE
INITIAL INTENSITY OF 50 KTS IS ASSESSED WITH MEDIUM CONFIDENCE
BASED ON THE AGENCY DVORAK AND OBJECTIVE INTENSITY ESTIMATES LISTED
BELOW.

INITIAL WIND RADII BASIS: OBJECTIVE BEST TRACK 

CURRENT STEERING MECHANISM: SOUTHWESTERN PERIPHERY OF A DEEP-LAYER
SUBTROPICAL RIDGE POSITIONED TO THE NORTHEAST.

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T3.0 - 45 KTS
   RJTD: T2.5 - 35 KTS
   RCTP: T3.5 - 55 KTS
   KNES: T3.5 - 55 KTS
   CIMSS SATCON: 47 KTS AT 190100Z
   CIMSS ADT: 49 KTS AT 190010Z
   CIMSS AIDT: 41 KTS AT 190010Z
   CIMSS DPRINT: 45 KTS AT 190010Z
   CIMSS DMINT: 40 KTS AT 182205Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 10-15 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: STRONG EQUATORWARD

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: TS 09W IS FORECAST TO CONTINUE TRACKING
WEST-NORTHWESTWARD ALONG THE SOUTHWESTERN PERIPHERY OF THE
SUBTROPICAL RIDGE THROUGH TAU 24. NEAR TAU 24, RIDGING WILL EXTEND
OVER TO THE NORTH OF THE VORTEX WHICH WILL GUIDE THE SYSTEM MORE
WESTWARD.  A MIDLATITUDE SHORTWAVE TROUGH IS THEN EXPECTED TO
BRIEFLY BREAK DOWN THE RIDGE AS THE SYSTEM SKIRTS THE SOUTHERN
COAST OF CHINA. AFTER THE TROUGH PROPAGATES EASTWARD, RIDGING WILL
BUILD IN TO THE NORTHWEST, CAUSING 09W TO TAKE A WEST-SOUTHWESTWARD
TRACK THROUGH THE REMAINDER OF THE FORECAST PERIOD. AROUND TAU 60,
AN EMERGENCE OF THE VORTEX BACK OVER WATER WITHIN THE GULF OF
TONKIN IS FORECAST TO OCCUR WITH LANDFALL NEAR TAU 72 IN NORTHERN
VIETNAM. REGARDING INTENSITY, 09W IS FORECAST TO INTENSIFY OVER THE
NEXT 24 HOURS AS THE WIND FIELD FURTHER CONSOLIDATES AND THE
ENVIRONMENT REMAINS FAVORABLE. AS THE SYSTEM SKIRTS THE SOUTHERN
COAST OF CHINA, TERRAIN INTERACTION WILL CAUSE 09W TO WEAKEN. A
BRIEF PERIOD OF INTENSIFICATION IS LIKELY TO OCCUR ONCE THE VORTEX
EMERGES WITHIN THE GULF OF TONKIN DUE TO VERY WARM SEA SURFACE
TEMPERATURES (31 C). AFTER LANDFALL IN VIETNAM, 09W WILL RAPIDLY
WEAKEN WITH DISSIPATION FORECAST TO OCCUR NEAR END OF THE FORECAST
PERIOD (TAU 120).

MODEL DISCUSSION: NUMERICAL MODEL TRACK GUIDANCE IS IN GOOD
AGREEMENT THROUGH TAU 72 WITH A 135 NM CROSS-TRACK SPREAD AT TAU
72. AFTERWARD, MODELS BEGIN TO DIVERGE AS POTENTIAL INTERACTION
WITH THE INCREASED WESTERLIES ASSOCIATED WITH A DEVELOPING TROPICAL
CYCLONE FORECAST TO DEVELOP EAST OF LUZON IN THE 3-4 DAY PERIOD.
THIS WOULD PULL 09W BACK EASTWARD INTO THE GULF OF TONKIN WITH A
POSSIBILITY OF BRIEF REDEVELOPMENT. THIS SCENARIO IS MOSTLY DEPICTED
BY GFS AND THE GEFS AND IS CONSIDERED TO BE AN OUTLIER AT THIS
POINT. THE JTWC TRACK FORECAST IS PLACED WITH MEDIUM CONFIDENCE
THROUGH TAU 72 AND LOW CONFIDENCE THEREAFTER. INTENSITY GUIDANCE
CONTINUES TO BE SPLIT, WITH RAPID INTENSIFICATION (RI) AIDS
TRIGGERING. HAFS-A AND HWRF BOTH SUGGEST WEAKENING STARING AFTER
TAU 12 THROUGH THE APPROACH TO THE COAST OF CHINA. THE JTWC
INTENSITY FORECAST CALLS FOR INTENSIFICATION WITHOUT RI THROUGH TAU
24, BEFORE LAND INTERACTION BECOMES A FACTOR. OVERALL, THERE IS LOW
CONFIDENCE IN THE INTENSITY FORECAST DUE TO THE SPREAD IN MODEL
GUIDANCE.

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