Advisories

WDPN32 PGTW 242100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 29W (CHAMPI) WARNING NR 
042//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 28.3N 123.8E
   INITIAL INTENSITY: 50 KTS
   GEOGRAPHIC REFERENCE: 419 NM SOUTHWEST OF SASEBO, JAPAN
   MOVEMENT PAST 6 HOURS: NORTH-NORTHEASTWARD AT 11 KTS
   SIGNIFICANT WAVE HEIGHT: 23 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS TROPICAL
STORM (TS) 29W AS A FULLY EXPOSED, SHALLOW, AND RAGGED CIRCULATION,
OVERWHELMED BY HIGH VERTICAL WIND SHEAR (VWS) AND DRY AIR. THE
241226Z ASCAT DATA REVEALS THE SYSTEM IS HIGHLY ASYMMETRICAL AND
FRONTAL, WITH ELEVATED WINDS CONFINED TO THE COLD SIDE OF THE
CIRCULATION. ENVIRONMENTAL ANALYSIS REVEALS A HOSTILE ENVIRONMENT,
CHARACTERIZED BY HIGH (30-35 KTS) VWS, COLD (25-26 C) SEA SURFACE
TEMPERATURES (SST), SIGNIFICANT DRY AIR ELIMINATING ANY CONVECTION,
NEGLIGIBLY OFFSET BY THE STRONG POLEWARD OUTFLOW PROVIDED BY THE
UPPER-LEVEL JET. THE INITIAL POSITION IS PLACED WITH MEDIUM
CONFIDENCE BASED ON THE RAGGED, PARTIALLY EXPOSED LOW-LEVEL
CIRCULATION CENTER. THE INITIAL INTENSITY OF 50 KTS IS ASSESSED
WITH MEDIUM CONFIDENCE BASED ON THE EARLIER ASCAT DATA, SUPPORTED
BY THE AGENCY DVORAK FIXES AND CIMSS AUTOMATED INTENSITY ESTIMATES
LISTED BELOW.

INITIAL WIND RADII BASIS: 241226Z ASCAT DATA

CURRENT STEERING MECHANISM: WESTERN FLANK OF A DEEP-LAYER
SUBTROPICAL RIDGE (STR) CENTERED SOUTHEAST OF HONSHU

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T3.0 - 45 KTS
   RJTD: T3.5 - 55 KTS
   RCTP: T2.5 - 35 KTS
   DEMS: T3.5 - 55 KTS
   CIMSS SATCON: 50 KTS AT 241710Z
   CIMSS ADT: 45 KTS AT 241910Z
   CIMSS AIDT: 46 KTS AT 241910Z
   CIMSS D-MINT: 54 KTS AT 241718Z
   CIMSS D-PRINT: 58 KTS AT 241840Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: HIGHLY UNFAVORABLE
   VWS: 30-35 KTS
   SST: 25-26 CELSIUS
   OUTFLOW: STRONG POLEWARD
   OTHER FACTORS: DRY AIR

ANALYSIS CONFIDENCE:
   INITIAL POSITION: MEDIUM
   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 (CHAMPI) IS FORECAST TO CONTINUE
TRACKING POLEWARD AS IT ROUNDS THE NORTHWESTERN PERIPHERY OF THE
STEERING STR FOR THE DURATION OF THE FORECAST PERIOD. 29W WILL
BEGIN EXTRATROPICAL TRANSITION IMMINENTLY. TRANSITION IS EXPECTED
TO BE COMPLETE NO LATER THAN TAU 36, BUT LIKELY MUCH EARLIER. THE
ENVIRONMENT IS EXPECTED TO BECOMING INCREASINGLY HOSTILE AS 29W
TRACKS POLEWARD, WITH SSTS CONTINUOUSLY DROPPING, VWS INCREASING AS
PROXIMITY TO THE UPPER-LEVEL JET DECREASES, AND CONTINUED COPIOUS
AMOUNTS OF DRY AIR INUNDATING THE SYSTEM. THE DEGRADING ENVIRONMENT
IS EXPECTED TO WEAKEN THE SYSTEM THROUGH TAU 36. BETWEEN TAU 36-48,
29W IS FORECAST TO MAINTAIN INTENSITY AS IT BECOMES A FULLY
EXTRATROPICAL SYSTEM. BETWEEN TAU 12-36, IT IS POSSIBLE THAT 29W
WILL DEGRADE INTO A TROUGH AND THEREFORE DISSIPATE PRIOR TO
COMPLETING EXTRATROPICAL TRANSITION.

MODEL DISCUSSION: DETERMINISTIC MODEL TRACK GUIDANCE IS IN GOOD
AGREEMENT THROUGH TAU 48, WITH THE EXCEPTION OF NAVGEM AND GALWEM,
WHICH ARE FARTHER POLEWARD THAN THE BULK OF GUIDANCE. DISCOUNTING
THOSE MODEL SOLUTIONS, THE JTWC TRACK FORECAST IS PLACED WITH HIGH
CONFIDENCE NEAR THE MULTI-MODEL CONSENSUS. RELIABLE INTENSITY AIDS
ARE IN STRONG AGREEMENT IN A STEADY WEAKENING THROUGH TAU 36, WITH
SEVERAL MODELS ALSO DEPICTING A FLAT INTENSITY BETWEEN TAU 36-48.
AS A RESULT, THE JTWC INTENSITY FORECAST IS ASSESSED WITH HIGH
CONFIDENCE. 

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