Advisories

WDPN33 PGTW 110300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 14W (CHAN-HOM) WARNING NR 017//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 36.8N 143.7E
   INITIAL INTENSITY: 50 KTS
   GEOGRAPHIC REFERENCE: 173 NM EAST-NORTHEAST OF NARITA AIRPORT
   MOVEMENT PAST 6 HOURS: WESTWARD AT 18 KTS
   SIGNIFICANT WAVE HEIGHT: 29 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS A FULLY
EXPOSED LOW-LEVEL CIRCULATION CENTER (LLCC) MOVING BRISKLY WESTWARD
TOWARD CENTRAL HONSHU. THE ARRANGEMENT OF CONVECTION AND DRY AIR
AROUND THE CIRCULATION HAS ROTATED COUNTERCLOCKWISE OVER THE PAST
SIX HOURS, WITH LIMITED CONVECTION NOW CONFINED SOUTHWEST AND SOUTH
OF THE LLCC, WHILE A DEEP-LAYER DRY SLOT HAS ENVELOPED THE EASTERN
SEMICIRCLE AND IS NOW ROTATING INTO THE NORTHERN SEMICIRCLE. AFTER
PASSING OVER A COLD OCEAN EDDY EARLIER, THE STORM IS NOW OVER A
WARMER EDDY OF 26C TO 27C SEA SURFACE TEMPERATURES, YET CONVECTIVE
COVERAGE HAS NOT IMPROVED. THE STORM CONTINUES TO DEGRADE OVERALL
IN TERMS OF CONVECTIVE STRUCTURE. THE CIRCULATION REMAINS VIGOROUS,
HOWEVER, AND A RECENT 102359Z ASCAT-C SCATTEROMETER PASS REVEALED
THAT THE WIND FIELD REMAINS PERSISTENT DESPITE THE STORM'S
DEGRADING SATELLITE APPEARANCE, WITH 45 TO 50 KT WINDS ARCING
THROUGH THE NORTHERN SEMICIRCLE OF THE CIRCULATION. THE INITIAL
INTENSITY IS THUS BUMPED TO 50 KT. GALE-FORCE WIND RADII HAVE
EXPANDED RELATIVE TO SIX HOURS AGO, AND ARE NOW APPROACHING COASTAL
AREAS OF NORTHERN HONSHU.

INITIAL WIND RADII BASIS: SCATTEROMETER DATA 

CURRENT STEERING MECHANISM: SUBTROPICAL RIDGE TO THE NORTH AND A
DEEP UPPER LOW TO THE SOUTH

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T3.0 - 45 KTS
   RJTD: T2.5 - 35 KTS
   RCTP: T2.5 - 35 KTS
   CIMSS D-MINT: 40 KTS AT 102031Z
   CIMSS D-PRINT: 37 KTS AT 102330Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINAL
   VWS: 25-30 KTS
   SST: 26-27 CELSIUS
   OUTFLOW: MODERATE WESTWARD
   OTHER FACTORS: DEEP-LAYER DRY AIR WRAPPING AROUND THE EASTERN
AND NORTHERN SEMICIRCLES

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: TROPICAL STORM 14W (CHAN-HOM) CONTINUES TO
MARCH TOWARD CENTRAL HONSHU WITH PACE AS IT PINWHEELS AROUND THE
NORTHERN PERIPHERY OF A DEEP UPPER-LEVEL LOW TO ITS SOUTH. THIS
UPPER LOW IS IMPOSING STRONG EASTERLY WIND SHEAR AND INJECTING
DEEP-LAYER DRY AIR INTO THE CIRCULATION, WHICH SHOULD PREVENT
INTENSIFICATION IN THE FINAL HOURS PRIOR TO LANDFALL IN JAPAN. THE
CURRENTLY BARREN CONVECTIVE STRUCTURE SUPPORTS THIS CONCLUSION,
THOUGH A POTENT WIND FIELD WILL NEVERTHELESS MOVE ASHORE. LANDFALL
IN IBARAKI PREFECTURE, JAPAN IS EXPECTED IN LESS THAN 12 HOURS,
FOLLOWED BY A GENERALLY WESTWARD TRACK ACROSS THE MOUNTAINOUS
TERRAIN OF CENTRAL HONSHU, WHICH WILL RESULT IN QUICK WEAKENING
BELOW TROPICAL STORM INTENSITY. EMERGENCE OVER THE SOUTHERN SEA OF
JAPAN IS EXPECTED IN ABOUT 24 HOURS, WHERE HOSTILE ENVIRONMENTAL
CONDITIONS CONSISTING OF STRONG WIND SHEAR AND DRY AIR ARE EXPECTED
TO PREVENT REDEVELOPMENT. INDEED, MODELS AGREE THAT 14W WILL ARRIVE
IN THE SEA OF JAPAN IN A STATE OF SUCH DISREPAIR THAT ITS STRUCTURE
WILL UNRAVEL, RESULTING IN DISSIPATION IN AROUND 48 HOURS WITHIN AN
UNFAVORABLE ENVIRONMENT.

MODEL DISCUSSION: PHYSICS-BASED AND AI-BASED MODEL TRACK GUIDANCE
HAS COME INTO TIGHTER AGREEMENT OVER THE PAST SIX HOURS AND
CONNOTES HIGH CONFIDENCE IN THE TRACK FORECAST. THE JTWC FORECAST
TRACK LEANS TOWARD THE SOUTHERN HALF OF THE GUIDANCE ENVELOPE
THROUGH 12 HOURS, THEN CLOSE TO THE MULTI-MODEL CONSENSUS
THEREAFTER. INTENSITY GUIDANCE IS ALSO IN TIGHT AGREEMENT, AND THE
JTWC INTENSITY FORECAST IS MADE WITH HIGH CONFIDENCE.

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