Advisories

WDPN32 PGTW 240300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 29W (CHAMPI) WARNING NR 039//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 24.8N 123.3E
   INITIAL INTENSITY: 65 KTS
   GEOGRAPHIC REFERENCE: 100 NM EAST OF TAIPEI, TAIWAN
   MOVEMENT PAST 6 HOURS: EAST-NORTHEASTWARD AT 10 KTS
   SIGNIFICANT WAVE HEIGHT: 30 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
TY 29W HAS RAPIDLY WEAKENED OVER THE PAST SIX HOURS DUE PRIMARILY
TO LAND INTERACTION WITH TAIWAN. THE SYSTEM HAS COMPLETED A LOOP TO
THE EAST OF TAIWAN AND IS RETURNING TO A POLEWARD TRAJECTORY.
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS A PARTIALLY
EXPOSED LOW-LEVEL CIRCULATION WITH LIMITED AND RELATIVELY SHALLOW
CONVECTION ALONG THE EASTERN PERIPHERY. THE INITIAL POSITION IS
PLACED WITH MEDIUM CONFIDENCE BASED ON A GROUPING OF SUBJECTIVE
GEOSTATIONARY SATELLITE POSITION AND RADAR FIXES FROM VARIOUS
REPORTING AGENCIES. THE INITIAL INTENSITY OF 65 KTS IS ASSESSED
WITH MEDIUM CONFIDENCE BASED ON THE LOW END OF SUBJECTIVE DVORAK
AND AUTOMATED INTENSITY ESTIMATES LISTED BELOW, AS WELL AS A 232143Z
SENTINEL-1 SAR PASS INDICATING A LARGE BAND OF 60-65 KNOT WINDS
SOUTHEAST OF THE CIRCULATION CENTER.

INITIAL WIND RADII BASIS: OBJECTIVE BEST TRACK 

CURRENT STEERING MECHANISM: DEEP-LAYER SUBTROPICAL RIDGE (STR) TO
THE EAST

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T4.5 - 77 KTS
   RJTD: T4.5 - 77 KTS
   RCTP: T4.0 - 65 KTS
   CIMSS ADT: 92 KTS AT 232330Z
   CIMSS AIDT: 77 KTS AT 232330Z
   CIMSS D-MINT: 70 KTS AT 232053Z
   CIMSS D-PRINT: 60 KTS AT 232330Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: UNFAVORABLE
   VWS: 10-15 KTS
   SST: 26-27 CELSIUS
   OUTFLOW: STRONG POLEWARD

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

3. FORECAST REASONING.

SIGNIFICANT FORECAST CHANGES: FORECAST INTENSITIES HAVE DECREASED
AND THE INITIAL PORTION OF THE FORECAST TRACK HAS SHIFTED EASTWARD
SLIGHTLY FROM THE PREVIOUS FORECAST DUE TO OBSERVED POSITION AND
STRUCTURAL CHANGES.

FORECAST DISCUSSION: AFTER INITIALLY POLEWARD MOTION, TY 29W WILL
TURN NORTH-NORTHEASTWARD AROUND THE PERIPHERY OF THE CURRENT
SUBTROPICAL STEERING RIDGE THROUGH THE FORECAST PERIOD. EXTRATROPICAL 
TRANSITION WILL BEGIN BY TAU 36 AS THE SYSTEM INTERACTS WITH A 
DEVELOPING MID-LATITUDE TROUGH TO THE NORTHWEST. TY 29W WILL MERGE 
WITH THE TROUGH AND BECOME FULLY EMBEDDED BY TAU 60. STEADY WEAKENING 
WILL OCCUR PRIOR TO EXTRATROPICAL TRANSITION DUE TO ONGOING 
ENTRAINMENT OF DRIER AIR FROM THE WEST, PASSAGE OVER MARGINAL (25-26C) 
SEA SURFACE TEMPERATURES, AND INCREASING VERTICAL WIND SHEAR. 

MODEL DISCUSSION: NUMERICAL MODEL TRACK FORECAST GUIDANCE REMAINS
IN GOOD AGREEMENT REGARDING THE OVERALL SCENARIO. THE PHYSICS-BASED
AND AI MODEL CONSENSUSES ARE SPREAD BY ABOUT 50 NM FROM TAU 24
ONWARD, WITH THE AI CONSENSUS SITUATED TO THE SOUTH AND BOTH DEPICTING
SIMILAR TRACK SPEEDS. THE CURRENT JTWC FORECAST MAINLY SPLITS THE
DIFFERENCE BETWEEN THE TWO CONSENSUS SOLUTIONS AND, ALTHOUGH LYING
A BIT TO THE EAST EARLY ON DUE TO RECENT STORM MOTION, IS
CONSISTENT WITH THE PREVIOUS JTWC TRACK FORECAST AFTER TAU 24.
INTENSITY FORECAST GUIDANCE IS IN VERY GOOD AGREEMENT REGARDING A
CONTINUED STEADY WEAKENING TREND AND FLATLINE TREND FOLLOWING
EXTRATROPICAL TRANSITION AS THE SYSTEM MERGES INTO A MID-LATITUDE
TROUGH AND LIKELY BECOMES INDISTINGUISHABLE AS A SEPARATE
CIRCULATION.

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