WDPN31 PGTW 182100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 09W (WIPHA) WARNING NR 
002//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 19.8N 120.8E
   INITIAL INTENSITY: 45 KTS
   GEOGRAPHIC REFERENCE: 399 NM EAST-SOUTHEAST OF HONG KONG
   MOVEMENT PAST 6 HOURS: WEST-NORTHWESTWARD AT 13 KTS
   SIGNIFICANT WAVE HEIGHT: 20 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS TROPICAL
STORM 09W (WIPHA) WITH IMPROVED CENTRAL CONVECTION NOW FULLY
OBSCURING THE LOW-LEVEL CIRCULATION CENTER (LLCC) AND AN OVERALL
CONSOLIDATED APPEARANCE COMPARED TO 6 HOURS AGO. AN 181726Z AMSR2
37 GHZ MICROWAVE IMAGE REVEALED A BROAD MICROWAVE EYE FEATURE AND
CONVECTIVE BANDING TIGHTLY WRAPPING INTO THE CENTER. ENVIRONMENTAL
ANALYSIS INDICATES THAT 09W IS IN A FAVORABLE ENVIRONMENT
CHARACTERIZED BY MODERATE EQUATORWARD OUTFLOW ALOFT, LOW TO
MODERATE (15-20 KTS) EASTERLY VERTICAL WIND SHEAR, AND WARM (29-30
C) SEA SURFACE TEMPERATURES. THE INITIAL POSITION IS PLACED WITH
HIGH CONFIDENCE BASED ON THE MENTIONED AMSR2 MICROWAVE IMAGE. THE
INITIAL INTENSITY OF 45 KTS IS ASSESSED WITH MEDIUM CONFIDENCE
BASED ON THE AGENCY DVORAK AND OBJECTIVE INTENSITY ESTIMATES LISTED
BELOW.

INITIAL WIND RADII BASIS: PERSISTENCE FROM THE 181255Z AND 181346Z
ASCAT PASSES

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

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T3.5 - 55 KTS
   RJTD: T2.5 - 35 KTS
   RCTP: T3.0 - 45 KTS
   KNES: T3.0 - 45 KTS
   CIMSS SATCON: 37 KTS AT 181750Z
   CIMSS ADT: 41 KTS AT 181800Z
   CIMSS AIDT: 36 KTS AT 181800Z
   CIMSS DPRINT: 38 KTS AT 181800Z
   CIMSS DMINT: 37 KTS AT 181750Z
   

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 15-20 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: MODERATE EQUATORWARD

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

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 TURN THE TRAJECTORY MORE
WESTWARD. AN INITIAL LANDFALL IS CURRENTLY FORECAST TO OCCUR AROUND
TAU 36, NEAR HONG KONG. AFTER LANDFALL, A MIDLATITUDE SHORTWAVE
TROUGH IS THEN EXPECTED TO BRIEFLY BREAK DOWN THE RIDGE OVER
CENTRAL CHINA 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. NEAR TAU 72, AN EMERGENCE OF
THE VORTEX BACK OVER WATER WITHIN THE GULF OF TONKIN IS FORECAST TO
OCCUR WITH A SECOND LANDFALL SOON AFTER IN NORTHERN VIETNAM.
REGARDING INTENSITY, 09W IS FORECAST TO INTENSIFY OVER THE NEXT 24
HOURS AS TERRAIN INTERACTION WITH NORTHERN LUZON DECREASES AND THE
WIND FIELD FURTHER CONSOLIDATES. 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 (30-31 C). AFTER THE SECOND LANDFALL IN VIETNAM, 09W
WILL RAPIDLY WEAKEN WITH DISSIPATION NEAR END OF THE FORECAST
PERIOD (TAU 120).

MODEL DISCUSSION: NUMERICAL MODEL TRACK GUIDANCE IS IN GOOD
AGREEMENT THROUGH TAU 72 WITH AN 80 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 SCENARIO IS MOSTLY DEPICTED BY GFS AND THE GEFS AND IS
CONSIDERED TO BE AN OUTLIER AT THIS POINT. INTENSITY GUIDANCE IS IN
POOR AGREEMENT WITH SOME RAPID INTENSIFICATION (RI) AIDS TRIGGERING
ON THIS MODEL RUN. HAFS-A AND HWRF, ON THE OTHER HAND, HAVE A MUCH
MORE NORTHWARD TRACK WITH SIGNIFICANT MORE LAND INTERACTION WITH
EASTERN CHINA. AS SUCH, THEY QUICKLY DISSIPATE 09W BY TAU 72. THE
JTWC INTENSITY FORECAST CALLS FOR INTENSIFICATION, SIMILAR TO THE
RI AIDS, THROUGH TAU 24. OVERALL, THE JTWC INTENSITY FORECAST IS
PLACED WITH LOW CONFIDENCE.

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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