WDPN31 PGTW 121500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 01W (WUTIP) WARNING NR 
009//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 17.4N 109.2E
   INITIAL INTENSITY: 50 KTS
   GEOGRAPHIC REFERENCE: 99 NM NORTH-NORTHEAST OF DA NANG, VIETNAM
   MOVEMENT PAST 6 HOURS: WEST-NORTHWESTWARD AT 07 KTS
   SIGNIFICANT WAVE HEIGHT: 21 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS TROPICAL
STORM 01W (WUTIP) WITH PERSISTENT CONVECTION NOW MORE ALIGNED WITH
THE LOW-LEVEL CIRCULATION CENTER (LLCC). THE CLOUD TOPS JUST SOUTH
OF THE CENTER ARE EXTREMELY COLD, MEASURING COLDER THAN -90 C.
ENVIRONMENTAL ANALYSIS INDICATES THAT 01W IS IN A FAVORABLE
ENVIRONMENT CHARACTERIZED BY STRONG EQUATORWARD OUTFLOW ALOFT,
MODERATE (15-20 KTS) NORTHEASTERLY VERTICAL WIND SHEAR, AND WARM
(29-30 C) SEA SURFACE TEMPERATURES. THE INITIAL POSITION IS PLACED
WITH MEDIUM CONFIDENCE BASED ON THE ANIMATED EIR SATELLITE IMAGERY.
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: PERSISTENCE 

CURRENT STEERING MECHANISM: A SUBTROPICAL RIDGE (STR) 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: T3.5 - 55 KTS
   CIMSS ADT: 39 KTS AT 121200Z
   CIMSS AIDT: 36 KTS AT 121200Z
   CIMSS DPRINT: 44 KTS AT 121200Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 15-20 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: 01W IS FORECAST TO TRACK NORTHWESTWARD THROUGH
TAU 12 BEFORE BEGINNING TO ROUND THE RIDGE AXIS AND COMMENCING A
NORTHWESTWARD TURN. THE TRACK HAS SHIFTED SLIGHTLY TO THE WEST WHEN
COMPARED TO THE PREVIOUS FORECAST AND NOW HAS THE VORTEX CENTER
PASSING JUST TO THE WEST OF HAINAN FROM TAU 12 TO 24. AFTER TAU 24,
01W IS FORECAST TO TRACK NORTHWESTWARD AND HEAD TOWARD THE WESTERN
EXTENT OF THE LEIZHOU PENINSULA. LANDFALL ALONG THE SOUTHERN COAST
OF MAINLAND CHINA IS FORECAST TO OCCUR BETWEEN TAU 36 AND 48.
REGARDING INTENSITY, 01W IS FORECAST TO SLIGHTLY INTENSIFY TO 55
KTS AT TAU 12 IN RESPONSE TO THE OVERALL FAVORABLE ENVIRONMENT. AFTER 
TAU 12, LAND INTERACTION WITH WESTERN COAST OF HAINAN WILL
DISRUPT THE SYSTEM AND CAUSE GRADUAL WEAKENING THROUGH TAU 48. AFTER 
MAKING LANDFALL, 01W WILL RAPIDLY WEAKEN DUE TO SIGNIFICANT TERRAIN 
INTERACTION. THE VORTEX IS THEN FORECAST TO COMPLETELY DISSIPATE BY 
TAU 72. 

MODEL DISCUSSION: NUMERICAL MODEL TRACK GUIDANCE IS IN GOOD
AGREEMENT WITH A 70 NM CROSS TRACK SPREAD AT TAU 48. THE GFS
DETERMINISTIC TRACKER IS A BIT OF AN OUTLIER, DEPICTING THE VORTEX
JUST OFF THE COAST AT TAU 48, WHICH IS NOTABLY SLOWER THAN THE
REMAINDER OF GUIDANCE. AS A RESULT, ALONG-TRACK SPREAD IS HIGHER,
AT AROUND 100 NM. AFTER TAU 48, ALONG TRACK SPREAD INCREASES
SIGNIFICANTLY DUE TO THE VERY SHALLOW AND WEAK VORTEX SIGNATURE AS
THE SYSTEM DISSIPATES. OVERALL, THE JTWC TRACK FORECAST IS PLACED
WITH MEDIUM CONFIDENCE. INTENSITY GUIDANCE IS IN MODERATE
AGREEMENT, WITH ALL MODELS SUGGESTING WEAKENING AFTER TAU 12. THE
JTWC INTENSITY FORECAST IS ALSO PLACED WITH MEDIUM CONFIDENCE,
CLOSE TO THE MULTI-MODEL CONSENSUS.

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