Advisories

WDPN32 PGTW 240900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 29W (CHAMPI) WARNING NR 
040//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 26.8N 123.3E
   INITIAL INTENSITY: 55 KTS
   GEOGRAPHIC REFERENCE: 242 NM WEST OF KADENA AB
   MOVEMENT PAST 6 HOURS: NORTHWARD AT 19 KTS
   SIGNIFICANT WAVE HEIGHT: 24 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
TROPICAL STORM (TS) 29W HAS RAPIDLY WEAKENED. ANIMATED
MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS A PARTIALLY EXPOSED
LOW-LEVEL CIRCULATION CENTER (LLCC) WITH SHALLOW CONVECTION
CONFINED TO THE EASTERN PERIPHERY. OVER THE PAST 18 HOURS, THE
INNER CORE OF 29W INTERACTED WITH THE MOUNTAINOUS TERRAIN OF
TAIWAN. A COMPARISON OF THE 231245Z ASCAT-C AND 240112Z ASCAT-C
PASSES INDICATES THAT THE COMPACT CORE OF TYPHOON-FORCE WINDS HAS
GIVEN WAY TO A BROAD AREA OF LIGHT CENTRAL WINDS SURROUNDED BY
STORM-FORCE WINDS. A 232144Z SAR PASS BY SENTINEL-1C REVEALED THAT
THE INNER CORE WAS OPEN IN THE WESTERN SEMICIRCLE. SINCE THESE
PASSES, THE CIRCULATION HAS BECOME SOMEWHAT MORE SYMMETRICAL ON MSI
AS STRONG NORTHEASTERLY WINDS OFFSHORE OF CENTRAL CHINA CONVERGE
WITH STRONG SOUTHWESTERLY WINDS IMPACTING ISHIGAKIJIMA AND
MIYAKOJIMA. THE ENVIRONMENT IS UNFAVORABLE, WITH DRY AIR FROM
DOWNSLOPING WINDS OVER THE TAIWAN MOUNTAINS AND FROM THE ASIAN
CONTINENT ENTRAINING INTO THE CIRCULATION. MODERATE VERTICAL WIND
SHEAR (VWS), UPPER-LEVEL CONVERGENCE ALONG THE NORTHWEST PERIPHERY,
AND MARGINALLY WARM SEA SURFACE TEMPERATURES (SST) OF 26-27 DEGREES
CELSIUS FURTHER LIMIT REDEVELOPMENT. A POLEWARD OUTFLOW CHANNEL
PERSISTS BUT IS INSUFFICIENT TO OFFSET THESE NEGATIVE FACTORS. THE
INITIAL POSITION IS PLACED WITH MEDIUM CONFIDENCE BASED ON THE
PARTLY EXPOSED LLCC IN MSI. THE INITIAL INTENSITY IS SET AT A
POSSIBLY GENEROUS 55 KTS WITH MEDIUM CONFIDENCE, PRIMARILY BASED ON
THE SCATTEROMETER DATA. THIS ESTIMATE IS SIGNIFICANTLY LOWER THAN
THE AVERAGE OF THE SUBJECTIVE DVORAK FIXES AND FALLS WITHIN THE
RANGE OF THE CIMSS AUTOMATED INTENSITY ESTIMATES.

INITIAL WIND RADII BASIS: SCATTEROMETER DATA 

CURRENT STEERING MECHANISM: WESTERN FLANK OF A STR CENTERED
SOUTHEAST OF HONSHU

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T4.5 - 77 KTS
   RJTD: T4.5 - 77 KTS
   RCTP: T3.5 - 55 KTS
   CIMSS SATCON: 59 KTS AT 240457Z
   CIMSS ADT: 74 KTS AT 240540Z
   CIMSS AIDT: 61 KTS AT 240540Z
   CIMSS D-MINT: 40 KTS AT 240458Z
   CIMSS D-PRINT: 45 KTS AT 240540Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: UNFAVORABLE
   VWS: 15-20 KTS
   SST: 26-27 CELSIUS
   OUTFLOW: STRONG POLEWARD
   OTHER FACTORS: DRY AIR ENTRAINMENT

ANALYSIS CONFIDENCE:
   INITIAL POSITION: MEDIUM
   INITIAL INTENSITY: MEDIUM
   INITIAL WIND RADII: MEDIUM

3. FORECAST REASONING.

SIGNIFICANT FORECAST CHANGES: THE FORECAST HAS BEEN TRUNCATED TO 60
HOURS.

FORECAST DISCUSSION: TS 29W WILL TURN NORTHEASTWARD AS IT CROSSES
THE STR AXIS AND COMES UNDER THE INFLUENCE OF THE MID-LATITUDE
WESTERLY FLOW. THE SYSTEM WILL PASS OVER KYUSHU AROUND TAU 48. THE
ENVIRONMENT WILL BECOME INCREASINGLY HOSTILE, WITH SST DECREASING
TO BELOW 26 DEGREES CELSIUS, VWS INCREASING TO 20-30 KTS, AND DRY
AIR ERODING THE CORE STRUCTURE. THEREFORE, STEADY WEAKENING WILL
CONTINUE AS THE SYSTEM ENTERS THE BAROCLINIC ZONE AND UNDERGOES
EXTRATROPICAL TRANSITION (ETT). ETT WILL COMPLETE AROUND TAU 48 AS
THE SYSTEM APPROACHES KYUSHU. HOWEVER, IF THE SHALLOW SURFACE
CIRCULATION DEGENERATES MORE QUICKLY, IT MAY DISSIPATE INTO A
TROUGH BEFORE PASSING OVER KYUSHU.

MODEL DISCUSSION: BOTH PHYSICS-BASED AND AI MODELS ARE IN GOOD
AGREEMENT IN DEPICTING A RECURVING TRACK THAT BRINGS THE SYSTEM
CENTER OVER KYUSHU. A CROSS-TRACK SPREAD OF 105 NM EXISTS AT THE
FORECAST KYUSHU LANDFALL. THE BULK OF THE DYNAMICAL MODELS FAVOR A
LANDFALL POINT OVER NORTHERN KYUSHU, WHILE ECMWF AND THE AI MODELS
FAVOR A LANDFALL CORRIDOR ACROSS CENTRAL OR SOUTHERN KYUSHU. THE
JTWC FORECAST TRACK IS PLACED NEAR THE AI-MODEL MEAN, WHICH IS
CLOSEST TO GOOGLE DEEPMIND. ECMWF IS THE SOUTHERNMOST SOLUTION.
INTENSITY AIDS AGREE ON A GENERAL WEAKENING TREND. THE JTWC
INTENSITY FORECAST ALIGNS WITH HAFS-A AND DEEPMIND THROUGH TAU 12
AND THEN LEANS TOWARD GFS AND ECMWF FROM TAU 24 TO TAU 60.

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