WDPN31 PGTW 091500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 07W (LAN) WARNING NR 
008//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 24.7N 145.3E
   INITIAL INTENSITY: 55 KTS
   GEOGRAPHIC REFERENCE: 218 NM EAST OF IWO TO
   MOVEMENT PAST 6 HOURS: WEST-NORTHWESTWARD AT 07 KTS
   SIGNIFICANT WAVE HEIGHT: 25 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS MULTIPLE
DEEP CONVECTIVE BANDS SURROUNDING THE CENTER AND OBSCURING THE
LOW-LEVEL CIRCULATION CENTER (LLCC). WATER VAPOR IMAGERY ALSO
INDICATES EQUATORWARD OUTFLOW AND EASTWARD OUTFLOW INTO A TUTT CELL
TO THE EAST. THUS, ENVIRONMENTAL CONDITIONS REMAIN FAVORABLE. THE
INITIAL POSITION IS PLACED WITH MEDIUM CONFIDENCE BASED ON THE
GROUPING OF AGENCY POSITION FIXES. THE INITIAL INTENSITY OF 55 KTS
IS ASSESSED WITH MEDIUM CONFIDENCE BASED ON A CONSENSUS OF
SUBJECTIVE DVORAK AND AUTOMATED SATELLITE INTENSITY DATA AS WELL AS
A 090817Z SAR WIND SPEED IMAGE. ENVIRONMENTAL CONDITIONS REMAIN
FAVORABLE FOR INTENSIFICATION DUE TO WARM (30-31C) SEA SURFACE
TEMPERATURES (SST), LOW (0-5 KNOTS) VERTICAL WIND SHEAR (VWS), AND
GOOD OUTFLOW ALOFT.

INITIAL WIND RADII BASIS: PERSISTENCE 

CURRENT STEERING MECHANISM: DEEP-LAYERED SUBTROPICAL RIDGE (STR)
POSITIONED TO THE NORTHEAST. 


AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T3.5 - 55 KTS
   RCTP: T3.5 - 55 KTS
   KNES: T3.5 - 55 KTS
   CIMSS ADT: 49 KTS AT 091140Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 0-5 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: MODERATE EQUATORWARD
   OTHER FACTORS: MODERATE EASTWARD OUTFLOW INTO A TUTT CELL.

ANALYSIS CONFIDENCE:
   INITIAL POSITION: HIGH
   INITIAL INTENSITY: HIGH
   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 07W (LAN) WILL TRACK NORTHWESTWARD ALONG
THE SOUTHWESTERN PERIPHERY OF THE DEEP-LAYERED SUBTROPICAL RIDGE
(STR) POSITIONED TO THE NORTHEAST THROUGH TAU 24. BY TAU 36, THE
STR WILL SHIFT EAST AND ERODE SLIGHTLY AS A MID-LATITUDE TROUGH
PROPAGATES EASTWARD NORTH OF HOKKAIDO. BY TAU 48, THE STR WILL
REORIENT WHICH WILL GENERALLY ACCELERATE THE SYSTEM 
NORTH-NORTHWESTWARD WITHIN THE ENHANCED FLOW ON THE WESTERN
PERIPHERY OF THE RIDGE. BY TAU 72, THE STR IS EXPECTED TO EXTEND
WESTWARD WHICH WILL THEN STEER 07W NORTHWESTWARD TOWARD YOKOSUKA,
JAPAN THROUGH THE END OF THE FORECAST. IN TERMS OF INTENSITY, THE
FAVORABLE ENVIRONMENT WILL FUEL A STEADY INTENSIFICATION TO A PEAK
OF 85KTS BETWEEN TAUS 48-72. AFTERWARD, COOLING SSTS DUE TO
UPWELLING IN RELATIVELY SHALLOW WATERS NEAR THE COAST OF HONSHU
WILL GRADUALLY WEAKEN THE SYSTEM, DOWN TO 65 KNOTS BY TAU 120.

MODEL DISCUSSION: NUMERICAL MODEL GUIDANCE REMAINS IN GOOD
AGREEMENT WITH A 135NM SPREAD IN SOLUTIONS AT TAU 72. AFTER TAU 72,
GUIDANCE GRADUALLY DIVERGES WITH A 233 NM SPREAD IN SOLUTIONS AND 
RESULTS IN SOME CROSS-TRACK UNCERTAINTY BY TAU 120. BOTH THE
090600Z ECMWF (EPS) AND GFS (GEFS) ENSEMBLES DEPICT A SIMILAR
SPREAD WITH MODERATE UNCERTAINTY (MEDIUM CONFIDENCE IN THE JTWC
FORECAST TRACK) IN THE EXACT TRACK NEAR HONSHU. THIS LENDS OVERALL
HIGH CONFIDENCE TO THE JTWC TRACK FORECAST THROUGH TAU 72, WITH
MEDIUM CONFIDENCE BY TAU 120. THE INTENSITY GUIDANCE REMAINS IN
FAIR AGREEMENT WITH A STEADY INTENSIFICATION TO A PEAK OF 85 KNOTS.
ADDITIONALLY, AS INDICATED IN THE 091200Z COAMPS-TC ENSEMBLE, RAPID
INTENSIFICATION (RI) IS POSSIBLE WITHIN THE NEXT 36-48 HOURS WITH
PEAK PROBABILITIES OF 60 TO 80 PERCENT. OVERALL, THE JTWC INTENSITY
FORECAST IS ASSESSED WITH MEDIUM CONFIDENCE AND FOLLOWS CLOSELY TO
THE MULTI-MODEL CONSENSUS. 


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