Advisories

WDPN32 PGTW 251500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 29W (CHAMPI) WARNING NR 
045//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 30.7N 126.3E
   INITIAL INTENSITY: 40 KTS
   GEOGRAPHIC REFERENCE: 225 NM SOUTHWEST OF SASEBO, JAPAN
   MOVEMENT PAST 6 HOURS: NORTHEASTWARD AT 09 KTS
   SIGNIFICANT WAVE HEIGHT: 18 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
TROPICAL STORM (TS) 29W REMAINS DEVOID OF CONVECTION WITH
WIDESPREAD CIRRUS OVER THE NORTHERN PERIPHERY ASSOCIATED WITH A JET
STREAM TO THE NORTH. ANIMATED ENHANCED INFRARED (EIR) SATELLITE
IMAGERY DEPICTS A PARTIALLY EXPOSED LOW-LEVEL CIRCULATION CENTER
THAT CONTINUES TO ELONGATE ALONG A NORTH-NORTHEAST TO
SOUTH-SOUTHWEST AXIS. AN ASCAT-B PASS AT 251144Z AND AN RCM-1 SAR
PASS AT 250932Z INDICATE A HIGHLY ASYMMETRIC WIND FIELD CONSISTING
OF A LONG FETCH OF GALE-FORCE WINDS ALONG THE NORTHERN PERIPHERY AS
LOW-LEVEL AIR IS FUNNELED EQUATORWARD FROM THE KOREA STRAIT. TS 29W
IS TRAVERSING A HIGHLY UNFAVORABLE ENVIRONMENT OF SEA SURFACE
TEMPERATURES (SST) COOLER THAN 26 DEGREES CELSIUS IN A DRY, STABLE
AIRMASS WITH MODERATE TO HIGH VERTICAL WIND SHEAR. THE INITIAL
POSITION IS PLACED WITH HIGH CONFIDENCE NEAR THE PGTW FIX BASED ON
THE SCATTEROMETER DATA. THE INITIAL INTENSITY HAS BEEN LOWERED TO
40 KTS WITH HIGH CONFIDENCE BASED ON THE SCATTEROMETER DATA.

INITIAL WIND RADII BASIS: SCATTEROMETER DATA 

CURRENT STEERING MECHANISM: NORTHWESTERN FLANK OF A LOW- TO
MID-LEVEL SUBTROPICAL RIDGE CENTERED SOUTHEAST OF HONSHU

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: NO CURRENT ESTIMATE
   RJTD: T2.0 - 30 KTS
   RCTP: T1.5 - 25 KTS
   CIMSS ADT: 39 KTS AT 251140Z
   CIMSS AIDT: 58 KTS AT 251140Z
   CIMSS D-MINT: 30 KTS AT 250859Z
   CIMSS D-PRINT: 28 KTS AT 251140Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: HIGHLY UNFAVORABLE
   VWS: 20-25 KTS
   SST: 25-26 CELSIUS
   OUTFLOW: STRONG POLEWARD
   OTHER FACTORS: DRY AIRMASS AND STABLE ATMOSPHERE

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 29W WILL CONTINUE TO TURN EASTWARD AS IT
BECOMES EMBEDDED IN DEEP-LAYER WESTERLY FLOW, MAKING LANDFALL OVER
SOUTHERN KYUSHU BETWEEN TAU 12 AND TAU 24 IF THE LOW-LEVEL
CIRCULATION REMAINS COHERENT. IT IS BECOMING INCREASINGLY LIKELY
THAT THE CIRCULATION WILL DEGENERATE INTO A TROUGH AS IT APPROACHES
OR JUST AFTER IT PASSES OVER KYUSHU. SST WILL REMAIN COOL, AND
VERTICAL WIND SHEAR WILL INCREASE TO 30-40 KTS BY TAU 12.
BAROCLINIC INTENSIFICATION IS ALSO UNLIKELY, GIVEN THE WEAK THERMAL
ADVECTION AND LACK OF STRONG UPPER-LEVEL SUPPORT. EXTRATROPICAL
TRANSITION (ETT) WILL CONTINUE AS THE SYSTEM APPROACHES KYUSHU. IF
THE LOW LEVEL CIRCULATION REMAINS COHERENT, THE SYSTEM IS EXPECTED
TO COMPLETE ETT WITHIN 24 HOURS. OTHERWISE, THE CIRCULATION MAY
DEGENERATE INTO A TROUGH AS IT APPROACHES OR PASSES OVER KYUSHU.

MODEL DISCUSSION: TRACK GUIDANCE IS IN EXCELLENT AGREEMENT THROUGH
THE KYUSHU LANDFALL, WITH ALL SOLUTIONS DEPICTING LANDFALL OVER
SOUTHERN KYUSHU. ALL BUT NAVGEM KEEP THE SYSTEM CENTER OFFSHORE
AFTER PASSING OVER KYUSHU. THE JTWC FORECAST TRACK IS POSITIONED
NEAR THE CENTER OF THE GUIDANCE ENVELOPE, CLOSE TO THE MULTI-MODEL
CONSENSUS. THE INTENSITY GUIDANCE IS ALSO TIGHT, WITH GFS, HAFS-A,
AND GOOGLE DEEPMIND SHOWING CONTINUED DECAY. THE JTWC INTENSITY
FORECAST FOLLOWS THIS TREND AND IS SET NEAR THE CENTER OF THE
GUIDANCE ENVELOPE, SLIGHTLY BELOW HAFS-A BUT ABOVE DEEPMIND.

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