Advisories

WDPN32 PGTW 250900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 29W (CHAMPI) WARNING NR 
044//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 30.1N 125.5E
   INITIAL INTENSITY: 45 KTS
   GEOGRAPHIC REFERENCE: 248 NM NORTH-NORTHWEST OF KADENA AB
   MOVEMENT PAST 6 HOURS: NORTHEASTWARD AT 14 KTS
   SIGNIFICANT WAVE HEIGHT: 24 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS A FULLY
EXPOSED LOW-LEVEL CIRCULATION CENTER (LLCC) LARGELY DEVOID OF
CONVECTION. A 250028Z ASCAT-B PASS REVEALED 45-KT WINDS CONFINED TO
THE WESTERN PERIPHERY, ASSOCIATED WITH A TIGHT SURFACE PRESSURE
GRADIENT BETWEEN TROPICAL STORM (TS) 29W AND A RIDGE OVER CHINA.
WINDS ALONG THE EASTERN PERIPHERY ARE BARELY GALE-FORCE, AND THE
CIRCULATION IS BECOMING STRETCHED ALONG A NORTH-NORTHEAST TO
SOUTH-SOUTHWEST AXIS. THE ENVIRONMENT IS HIGHLY UNFAVORABLE FOR
TROPICAL CYCLONE REDEVELOPMENT, CHARACTERIZED BY COOL SEA SURFACE
TEMPERATURES (SST) OF 25-26 DEGREES CELSIUS, MODERATE VERTICAL WIND
SHEAR (VWS), DRY SURROUNDING AIR, AND INCREASING ATMOSPHERIC
STABILITY. THE INITIAL POSITION IS PLACED WITH HIGH CONFIDENCE
BASED ON THE EXPOSED LLCC IN ANIMATED MSI. THE INITIAL INTENSITY IS
SET AT 45 KTS WITH MEDIUM CONFIDENCE BASED ON EARLIER SCATTEROMETER
DATA.

INITIAL WIND RADII BASIS: PERSISTENCE 

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

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T3.0 - 45 KTS
   RJTD: T2.5 - 35 KTS
   RCTP: T2.0 - 30 KTS
   CIMSS SATCON: 40 KTS AT 250439Z
   CIMSS ADT: 25 KTS AT 250540Z
   CIMSS AIDT: 34 KTS AT 250540Z
   CIMSS D-MINT: 29 KTS AT 250440Z
   CIMSS D-PRINT: 28 KTS AT 250540Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: HIGHLY UNFAVORABLE
   VWS: 15-20 KTS
   SST: 25-26 CELSIUS
   OUTFLOW: STRONG POLEWARD
   OTHER FACTORS: DRY AIRMASS AND HIGHER ATMOSPHERIC STABILITY

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

3. FORECAST REASONING.

SIGNIFICANT FORECAST CHANGES: THERE ARE NO SIGNIFICANT CHANGES TO
THE FORECAST FROM THE PREVIOUS WARNING.

FORECAST DISCUSSION: TS 29W IS ACCELERATING NORTHEASTWARD ALONG THE
NORTHWEST PERIPHERY OF THE STR. THE SYSTEM WILL CONTINUE TO TURN
EASTWARD AS IT BECOMES INCREASINGLY EMBEDDED IN THE MID-LATITUDE
WESTERLY FLOW, MAKING LANDFALL OVER KYUSHU BY TAU 24. THE
ENVIRONMENT DOES NOT SUPPORT TROPICAL REDEVELOPMENT. CONDITIONS
WILL BE HOSTILE DUE TO COOL SST, DRY AIR, AND A STABLE ATMOSPHERE.
BAROCLINIC INSTABILITY WILL BE QUITE LOW, WITH WEAK THERMAL
ADVECTION AND MINIMAL UPPER-LEVEL SUPPORT. THEREFORE, THE
CIRCULATION WILL CONTINUE TO SPIN DOWN, WITH THE WIND FIELD AND
INTENSITY PRIMARILY GOVERNED BY THE TIGHT PRESSURE GRADIENT BETWEEN
ADJACENT SYNOPTIC-SCALE SYSTEMS. A TEMPERATURE PROFILE FROM A
241700Z ATMS PASS INDICATES THAT THE SYSTEM RETAINS A WEAK WARM
CORE. COMPARED WITH PREVIOUS PASSES, THE CORE IS COOLING.
EXTRATROPICAL TRANSITION (ETT) WILL PROGRESS AS THE SYSTEM
APPROACHES KYUSHU AND MAY COMPLETE BY TAU 24 IF THE CIRCULATION
REMAINS COHERENT. OTHERWISE, THE VORTEX MAY DEGENERATE INTO A
TROUGH PRIOR TO THAT TIME.

MODEL DISCUSSION: TRACK GUIDANCE IS IN TIGHT AGREEMENT, WITH THE
CORE CLUSTER CONCENTRATED ON THE SOUTHERN SIDE OF THE GUIDANCE
ENVELOPE. DYNAMICAL MODELS OCCUPY THE POLEWARD SIDE OF THE
ENVELOPE, WHILE AI MODELS ARE MORE EQUATORWARD. THE JTWC TRACK
FORECAST IS NEARLY IDENTICAL TO THE PREVIOUS FORECAST. IT IS
POSITIONED NEAR THE AI-MODEL MEAN AND GOOGLE DEEPMIND AND SHOWS
LANDFALL OVER SOUTHERN KYUSHU FOLLOWED BY A TRACK SOUTH OF HONSHU.
THE INTENSITY GUIDANCE IS TIGHT AS WELL, WITH A SPREAD OF 5 KTS.
THE JTWC INTENSITY FORECAST IS ALIGNED WITH DEEPMIND THROUGH TAU 12
AND THEN HEDGES TOWARD GFS AND ECMWF FROM TAU 24 TO TAU 36. WITH
THE SYSTEM BECOMING LESS TROPICAL IN NATURE, THE WIND FIELD IS
EVOLVING, WITH THE STRONGEST WINDS NOT NECESSARILY LOCATED NEAR THE
CENTER OF THE CIRCULATION.

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