WDPN31 PGTW 231500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 02W (SEPAT) WARNING NR 
005//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 27.0N 143.0E
   INITIAL INTENSITY: 40 KTS
   GEOGRAPHIC REFERENCE: 526 NM SOUTH-SOUTHEAST OF YOKOSUKA, JAPAN
   MOVEMENT PAST 6 HOURS: NORTHWESTWARD AT 14 KTS
   SIGNIFICANT WAVE HEIGHT: 18 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS TROPICAL
STORM (TS) 02W (SEPAT) TUCKING UNDERNEATH THE PERSISTENT
CONVECTION, DISPLAYING AN IMPROVED APPEARANCE COMPARED TO 6 HOURS
AGO. THE VORTEX SEEMS TO BE BECOMING MORE VERTICALLY ALIGNED AS THE
SYSTEM DISTANCES ITSELF FROM THE EFFECTS OF THE TROPICAL UPPER
TROPOSPHERIC TROUGH (TUTT) CELL TO THE SOUTHWEST. A 231213Z GMI 89
GHZ MICROWAVE IMAGE SHOWS THE COMPACT CIRCULATION WITH TIGHTLY
WRAPPING LOW-LEVEL CLOUD LINES AND DEEP CONVECTION OBSCURING THE
CENTER. ENVIRONMENTAL ANALYSIS INDICATES THAT 02W IS IN A
MARGINALLY FAVORABLE ENVIRONMENT CHARACTERIZED BY MODERATE POLEWARD
OUTFLOW ALOFT, LOW (10-15 KTS) VERTICAL WIND SHEAR, AND WARM (28-29
C) SEA SURFACE TEMPERATURES. THE INITIAL POSITION AND INTENSITY ARE
BOTH PLACED WITH HIGH CONFIDENCE BASED ON A 231132Z METOP-B ASCAT
IMAGE. THE ASCAT IMAGE CONTINUES TO SHOW THE ASYMMETRIC NATURE OF
THE WIND FIELD, WITH THE STRONGEST WINDS CONFINED TO THE
NORTHEASTERN QUADRANT. AGENCY DVORAK FIXES AND OBJECTIVE INTENSITY
ESTIMATES FROM CIMSS ALSO SUPPORT THE INITIAL INTENSITY ASSESSMENT.

INITIAL WIND RADII BASIS: 231132Z METOP-B ASCAT SCATTEROMETER DATA 

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

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T2.5 - 35 KTS
   RJTD: T2.0 - 30 KTS
   RCTP: T2.0 - 30 KTS
   KNES: T2.5 - 35 KTS
   CIMSS SATCON: 44 KTS AT 231300Z
   CIMSS ADT: 34 KTS AT 231230Z
   CIMSS AIDT: 37 KTS AT 231230Z
   CIMSS DPRINT: 36 KTS AT 231230Z
   CIMSS DMINT: 33 KTS AT 231208Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY FAVORABLE
   VWS: 10-15 KTS
   SST: 28-29 CELSIUS
   OUTFLOW: MODERATE POLEWARD
   OTHER FACTORS: PRESSURE FROM THE TUTT CELL POSITIONED TO THE
SOUTHWEST

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

3. FORECAST REASONING.

SIGNIFICANT FORECAST CHANGES: THERE ARE NO SIGNIFICANT CHANGES TO
THE FORECAST FROM THE PREVIOUS WARNING.

FORECAST DISCUSSION: TS 02W IS FORECAST TO CONTINUE TRACKING
NORTH-NORTHWESTWARD ALONG THE SOUTHWESTERN PERIPHERY OF THE
SUBTROPICAL RIDGE THROUGH TAU 48 AS THE VORTEX APPROACHES THE
EASTERN COAST OF HONSHU. NEAR TAU 48, 02W WILL BEGIN TO ROUND THE
RIDGE AXIS AND TURN NORTHEASTWARD, SKIRTING THE COAST. AFTERWARD,
02W WILL ACCELERATE IN A NORTHEASTWARD DIRECTION THROUGH TAU
72 AS THE SYSTEM DISSIPATES. REGARDING INTENSITY, 02W IS FORECAST
TO MAINTAIN ITS CURRENT INTENSITY OVER THE NEXT 12 HOURS AS SHEAR
STAYS LOW AND SEA SURFACE TEMPERATURES REMAIN CONDUCIVE. HOWEVER,
THE POLEWARD OUTFLOW CHANNEL THAT IS CURRENTLY BEING TAPPED INTO
WILL QUICKLY DIMINISH AFTER TAU 12. ADDITIONALLY, SEA SURFACE
TEMPERATURES ARE EXPECTED TO BECOME BORDERLINE BY TAU 24 AND THEN
UNFAVORABLY COOL (25 C) BY TAU 36. SEA TEMPERATURES WILL ONLY
BECOME COOLER ALONG THE TRACK OF 02W, WHICH WILL CAUSE THE SYSTEM
TO WEAKEN AS IT APPROACHES THE COAST OF HONSHU, SOUTH OF YOKOSUKA.
SHEAR WILL THEN RAPIDLY INCREASE AND CAUSE THE SYSTEM TO ERODE AND
DISSIPATE NEAR TAU 72 AS THE VORTEX ACCELERATES OFF TO THE
NORTHEAST. IF THE VORTEX IS ABLE TO STAY A SUFFICIENT DISTANCE FROM
THE COAST, AN EXTRATROPICAL TRANSITION VICE DISSIPATION SCENARIO
COULD OCCUR.

MODEL DISCUSSION: NUMERICAL MODEL TRACK GUIDANCE IS IN GOOD
AGREEMENT WITH AN 80 NM CROSS-TRACK SPREAD AT TAU 48. ALONG-TRACK
SPREAD HAS NOTABLY INCREASED COMPARED TO 6 HOURS AGO. ALONG-TRACK
SPREAD AT TAU 48 IS AROUND 120 NM WITH GFS DETERMINISTIC BEING THE
SLOWEST WHILE NAVGEM IS THE FASTEST. AFTER TAU 48, TRACKERS BEGIN
TO DIVERGE DUE TO THE SHALLOW NATURE OF THE VORTEX AND INCREASING
TRACK SPEEDS. OVERALL, THE JTWC TRACK FORECAST IS PLACED WITH
MEDIUM CONFIDENCE, IN LINE WITH THE MULTI-MODEL CONSENSUS.
INTENSITY GUIDANCE IS IN MODERATE AGREEMENT WITH MODELS SUGGESTING
WEAKENING THROUGH TAU 48. HOWEVER, THERE IS SOME DISAGREEMENT AFTER
TAU 48. SOME MODELS ARE NOW HAVING THE SYSTEM MOMENTARILY
INTENSIFYING AFTER MAKING THE RECURVE VICE WEAKENING. THE JTWC
INTENSITY FORECAST CONTINUES WITH THE INITIAL PHILOSOPHY OF
DISSIPATION, BUT A CHANGE TO EXTRATROPICAL TRANSITION COULD OCCUR
DEPENDING ON FUTURE MODEL GUIDANCE. 

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