WDPN31 PGTW 230900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 02W (SEPAT) WARNING NR 
004//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 25.9N 143.9E
   INITIAL INTENSITY: 35 KTS
   GEOGRAPHIC REFERENCE: 604 NM SOUTH-SOUTHEAST OF YOKOSUKA, JAPAN
   MOVEMENT PAST 6 HOURS: NORTH-NORTHWESTWARD AT 15 KTS
   SIGNIFICANT WAVE HEIGHT: 15 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS TROPICAL
STORM (TS) 02W (SEPAT) WITH A PARTIALLY EXPOSED LOW-LEVEL
CIRCULATION CENTER (LLCC) AND VIGOROUS BURSTS OF CONVECTION WITHIN
THE NORTHERN PERIPHERY OF THE SYSTEM. A 230345Z AMSR2 89 GHZ
MICROWAVE IMAGE REVEALED THE EXPOSED LOW-LEVEL CLOUD LINES AND
FRAGMENTED CONVECTIVE BANDING ALONG THE EASTERN FLANK OF THE
CIRCULATION. ENVIRONMENTAL ANALYSIS INDICATES THAT 02W IS IN A
MARGINALLY FAVORABLE ENVIRONMENT CHARACTERIZED BY MODERATE POLEWARD
OUTFLOW ALOFT, MODERATE SOUTHERLY VERTICAL WIND SHEAR, AND WARM
(28-29 C) SEA SURFACE TEMPERATURES. THE TROPICAL UPPER TROPOSPHERIC
TROUGH (TUTT) CELL IS NOW POSITIONED TO THE SOUTHWEST OF THE SYSTEM
AND IS THE CAUSE OF THE ELEVATED SHEAR AND SIGNIFICANT VORTEX TILT.
THE INITIAL POSITION IS PLACED WITH HIGH CONFIDENCE BASED ON THE
PARTIALLY EXPOSED LLCC IN ANIMATED MSI. THE INITIAL INTENSITY OF 35
KTS IS ALSO ASSESSED WITH HIGH CONFIDENCE BASED ON THE CLOSE
AGREEMENT BETWEEN THE AGENCY DVORAK AND OBJECTIVE INTENSITY
ESTIMATES LISTED BELOW.

INITIAL WIND RADII BASIS: PERSISTENCE FROM THE 222330Z AND 230019Z
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: T2.5 - 35 KTS
   KNES: T2.5 - 35 KTS
   CIMSS ADT: 35 KTS AT 230600Z
   CIMSS AIDT: 37 KTS AT 230600Z
   CIMSS DPRINT: 30 KTS AT 230600Z
   CIMSS DMINT: 28 KTS AT 230347Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY FAVORABLE
   VWS: 15-20 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: MEDIUM

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 AS THE SYSTEM
ACCELERATES AND BEGINS TO DISSIPATE THROUGH THE REMAINDER OF THE
FORECAST PERIOD. REGARDING INTENSITY, 02W IS FORECAST TO BRIEFLY
AND MARGINALLY INTENSIFY OVER THE NEXT 12 HOURS AS THE VORTEX
TRACKS AWAY FROM THE EFFECTS OF THE TUTT CELL. HOWEVER, THE
POLEWARD OUTFLOW CHANNEL WILL SIMULTANEOUSLY WEAKEN, PUTTING A CAP
ON THE INTENSIFICATION TREND. BY TAU 24, SEA SURFACE TEMPERATURES
WILL BECOME BORDERLINE, AND BY TAU 36 THEY WILL BECOME UNFAVORABLY
COOL (25 C). SEA TEMPERATURES WILL ONLY BECOME COOLER, WHICH WILL
CAUSE 02W TO WEAKEN AS IT CLOSES IN ON THE COAST OF HONSHU. BY TAU
72, SHEAR WILL BEGIN TO RAPIDLY INCREASE AND THE SYSTEM TO
DISSIPATE NEAR TAU 72. 

MODEL DISCUSSION: NUMERICAL MODEL TRACK GUIDANCE IS IN GOOD
AGREEMENT WITH A 75 NM CROSS-TRACK SPREAD AT TAU 48 WITH MINIMAL
ALONG-TRACK SPREAD. AFTER TAU 48, TRACKERS BEGIN TO DIVERGE DUE TO
THE SHALLOW NATURE OF THE VORTEX AND INCREASING TRACK SPEEDS.
INTENSITY GUIDANCE IS SLIGHTLY SPLIT WITH HWRF AND COAMPS-TC (GFS
BASED) BOTH DEPICTING INTENSIFICATION OVER THE NEXT 12 HOURS WHILE
HAFS-A AND GFS BOTH DEPICT WEAKENING OVER THE SAME TIME PERIOD.
AFTER TAU 12, ALL MODELS AGREE ON STEADY WEAKENING THROUGH THE
REMAINDER OF THE FORECAST. OVERALL, THE JTWC INTENSITY FORECAST IS
PLACED WITH MEDIUM CONFIDENCE.

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