Advisories

WDPN33 PGTW 100300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 14W (CHAN-HOM) WARNING NR 
013//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 33.7N 149.7E
   INITIAL INTENSITY: 40 KTS
   GEOGRAPHIC REFERENCE: 503 NM EAST OF YOKOSUKA, JAPAN
   MOVEMENT PAST 6 HOURS: NORTHWESTWARD AT 07 KTS
   SIGNIFICANT WAVE HEIGHT: 16 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS TROPICAL
STORM (TS) 14W (CHAN-HOM) GAINING SOME CONVECTION OVER ITS
NORTHEASTERN QUADRANT OVER THE PAST SIX HOURS, WHILE THE LOW LEVEL
CIRCULATION CENTER (LLCC) REMAINS FULLY EXPOSED. ENHANCED POLEWARD
OUTFLOW IS ALSO VISIBLE IN MSI AS THE PREVIOUS UPPER LEVEL LOW
POSITIONED TO THE NORTH OF TS 14W RETREATS, AND OUTFLOW BECOMES
DOMINATED BY AN UPPER LEVEL LOW CENTERED OVER HONSHU. OTHERWISE,
ENVIRONMENTAL CONDITIONS ARE ASSESSED AS MARGINAL AS THE SYSTEM IS
IN AN AREA OF LOW TO MODERATE (15-20 KTS) VERTICAL WIND SHEAR
(VWS), BORDERLINE (26-27 C) SEA SURFACE TEMPERATURES, AND DRY AIR
ENTRAINMENT ON THE SOUTHWESTERN FLANK. THE INITIAL POSITION AND
INTENSITY ARE ASSESSED WITH HIGH CONFIDENCE BASED ON A BULLSEYE
092356Z METOP-B ASCAT IMAGE DEPICTING A WELL DEFINED SWATH OF 35 TO
40 KTS IN THE NORTHEASTERN QUADRANT.

INITIAL WIND RADII BASIS: 092356Z METOP-B ASCAT DATA

CURRENT STEERING MECHANISM: SUBTROPICAL RIDGE (STR) CENTERED TO THE
NORTHEAST NEAR THE ALEUTIAN ISLANDS

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T2.0 - 30 KTS
   RJTD: T2.0 - 30 KTS
   RCTP: T2.0 - 30 KTS
   CIMSS ADT: 30 KTS AT 092330Z
   CIMSS AIDT: 31 KTS AT 092330Z
   CIMSS D-PRINT: 31 KTS AT 092330Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINAL
   VWS: 15-20 KTS
   SST: 26-27 CELSIUS
   OUTFLOW: STRONG POLEWARD
   OTHER FACTORS: UPPER LEVEL LOW CENTERED OVER NORTHERN HONSHU AND
DRY AIR ENTRAINMENT

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 14W IS FORECAST TO TRACK NORTHWESTWARD OUT
TO TAU 12 AND THEN SUBSEQUENTLY TURNING WESTWARD UNDER THE STEERING
INFLUENCE OF THE SUBTROPICAL RIDGE (STR) CENTERED TO THE NORTHEAST
OVER THE ALEUTIAN ISLANDS. TS 14W IS FORECAST TO MAKE LANDFALL OVER
CENTRAL HONSHU JUST BEFORE TAU 36 AND REEMERGE OVER THE SEA OF
JAPAN (SOJ) BY TAU 48. TS 14W IS EXPECTED TO CONTINUE ON A WESTWARD
TRACK FOR THE REMAINDER OF THE FORECAST PERIOD, AT A SLOWER TRACK
SPEED ONCE ENTERING THE SOJ AS IT ENCOUNTERS INCREASED SHEAR.
REGARDING INTENSITY, TS 14W IS FORECAST TO INTENSIFY IN THE
SHORT-TERM AS IT APPROACHES A STRONG UPPER LEVEL LOW CENTERED OVER
NORTHERN HONSHU, ENHANCING OUTFLOW ALOFT. INTENSITY IS FORECAST TO
DECREASE JUST PRIOR TO LANDFALL AS THE POSITION OF THE UPPER LEVEL
LOW MOVES SOUTHEASTWARD OFF THE COAST OF JAPAN, DECREASING OUTFLOW
ALOFT IN ADDITION TO COLD (23-24 C) SSTS JUST OFF THE COAST OF
HONSHU AND INCREASED DRY AIR ENTRAINMENT. INTENSITY IS EXPECTED TO
FURTHER DECREASE AS TS 14W INTERACTS WITH THE TERRAIN OF JAPAN,
REEMERGING OVER THE SOJ BELOW TROPICAL STORM LEVELS. THE
INCREASINGLY HOSTILE CONDITIONS IN THE SOJ OF DRY AIR AND HIGH
(OVER 30 KTS) VWS RESULT IN FORECAST SUBTROPICAL TRANSITION (STT)
BEGINNING NO LATER THAN TAU 60 AND COMPLETING BY TAU 72 AS TS 14W
DISSIPATES OVER WATER.

MODEL DISCUSSION: TRACK MODEL GUIDANCE IS IN GOOD AGREEMENT OF
LANDFALL OVER HONSHU AROUND TAU 36 FOLLOWED BY REEMERGENCE INTO THE
SOJ WITH THE NOTABLE OUTLIER OF GOOGLE DEEPMIND, WHICH HAS SHIFTED
SOUTH AFTER TAU 24, TRACKING DIRECTLY OVER TOKYO AND KEEPING TS 14W
OVER THE WESTERN COAST OF HONSHU FOR THE REMAINDER OF THE FORECAST
PERIOD. THE OFFICIAL JTWC FORECAST IS THUS PLACED WITH MEDIUM
CONFIDENCE, ON THE SOUTHERN SIDE OF THE BULK OF MODEL GUIDANCE.
INTENSITY GUIDANCE IS IN GOOD AGREEMENT FOR THE REMAINDER OF THE
FORECAST PERIOD, WITH GOOGLE DEEPMIND IN LINE WITH THE INITIAL
INTENSIFICATION TREND FOLLOWED BY WEAKENING UPON LANDFALL, ALTHOUGH
IT DOES SHOW DISSIPATION BY TAU 60. THE OFFICIAL JTWC FORECAST
INTENSITY IS ASSESSED WITH HIGH CONFIDENCE, CLOSELY IN LINE WITH
THE MULTI-MODEL CONSENSUS. 

FORECAST CONFIDENCE:
   TRACK 00-72 HR: MEDIUM
   INTENSITY 00-72 HR: HIGH//
NNNN