Advisories

WDPN32 PGTW 022100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 26W (CHOI-WAN) WARNING NR 012//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 18.1N 144.7E
   INITIAL INTENSITY: 75 KTS
   GEOGRAPHIC REFERENCE: 185 NM NORTH-NORTHWEST OF SAIPAN
   MOVEMENT PAST 6 HOURS: NORTHWARD AT 05 KTS
   SIGNIFICANT WAVE HEIGHT: 29 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS TYPHOON
(TY) 26W (CHOI-WAN) WITH A COMPACT CORE AND A CENTRAL DENSE
OVERCAST (CDO) THAT CONTINUES TO SLIGHTLY ORBIT THE OBSCURED LOW
LEVEL CIRCULATION CENTER (LLCC). ALTHOUGH THE WESTERN FLANK OF THE
LOWER-LEVEL CIRCULATION REMAINS PARTIALLY EXPOSED IN AN AREA OF
DRIER AIR, THE INNER CORE IS ASSESSED TO BE WELL COCOONED FROM DRY
AIR ENTRAINMENT AS 26W CONTINUES TO BUILD STRONGER CONVECTIVE
BANDING ON THE EASTERN AND NORTHERN FLANKS. ENVIRONMENTAL
CONDITIONS ARE ASSESSED TO BE HIGHLY FAVORABLE WITH HIGH (140 KJ
PER CM SQUARED) OCEAN HEAT CONTENT (OHC), LOW (10-15 KTS) VERTICAL 
WIND SHEAR (VWS), AND EXTREMELY FAVORABLE OUTFLOW ALOFT AS 26W 
DEVELOPS A POLEWARD OUTFLOW CHANNEL IN ADDITION TO ITS ALREADY STRONG
EQUATORWARD OUTFLOW. THE INITIAL POSITION IS PLACED WITH LOW
CONFIDENCE BASED ON THE OBSCURED LLCC IN EIR. THE INITIAL INTENSITY IS
ASSESSED WITH MEDIUM CONFIDENCE, ON THE HIGHER END OF THE AGENCY
DVORAK FIXES AND OBJECTIVE ESTIMATES LISTED BELOW.

INITIAL WIND RADII BASIS: PERSISTENCE 

CURRENT STEERING MECHANISM: COMBINATION OF A NEAR-EQUATORIAL RIDGE
CENTERED TO THE SOUTHEAST AND A SUBTROPICAL RIDGE CENTERED TO THE
NORTHEAST

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T4.0 - 65 KTS
   RJTD: T4.0 - 65 KTS
   RCTP: T4.0 - 65 KTS
   CIMSS SATCON: 67 KTS AT 021557Z
   CIMSS ADT: 57 KTS AT 021730Z
   CIMSS AIDT: 51 KTS AT 021730Z
   CIMSS D-MINT: 64 KTS AT 021803Z
   CIMSS D-PRINT: 72 KTS AT 021730Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: HIGHLY FAVORABLE
   VWS: 10-15 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: STRONG POLEWARD AND EQUATORWARD

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

3. FORECAST REASONING.

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

FORECAST DISCUSSION: TY 26W IS FORECAST TO CONTINUE NORTH-
NORTHEASTWARD OUT TO TAU 36 UNDER THE PRIMARY INFLUENCE OF
THE NEAR-EQUATORIAL RIDGE (NER) CENTERED TO THE SOUTHEAST AS THE
PASSAGE OF A SHORTWAVE TROUGH TO THE NORTH IS CURRENTLY WEAKENING
THE WESTERN PERIPHERY OF A SUBTROPICAL RIDGE (STR) CENTERED TO THE
NORTHEAST. BY TAU 36, THE STR IS EXPECTED TO REORIENT AND BECOME
THE PRIMARY STEERING INFLUENCE, CAUSING A SLIGHT NORTH-NORTHWESTWARD 
TRACK UNTIL TAU 72, AT WHICH POINT 26W WILL ROUND THE STR AXIS AND 
ACCELERATE NORTHEASTWARD FOR THE REMAINDER OF THE FORECAST PERIOD. 
EXTRATROPICAL TRANSITION (ETT) IS EXPECTED TO BEGIN NO LATER THAN TAU 
96 AND COMPLETE BY TAU 120 AS CHOI-WAN CROSSES THE 26 C ISOTHERM AND 
BEGINS INTERACTING WITH THE UPPER-LEVEL WESTERLIES. REGARDING 
INTENSITY, 26W IS EXPECTED TO INTENSIFY OUT TO A PEAK OF 110 KTS 
BETWEEN TAUS 36 AND 48, WITH RAPID INTENSIFICATION (RI) OUT TO TAU 12 
AS 26W REMAINS IN A HIGHLY FAVORABLE ENVIRONMENT OF HIGH OHC, STRONG 
POLEWARD AND EQUATORWARD OUTFLOW ALOFT, AND LOW VWS. AFTER TAU 48, A 
GENERAL WEAKENING TREND IS FORECAST FOR THE REMAINDER OF THE FORECAST 
PERIOD AS OHC VALUES DECLINE AND VWS AND RESULTANT DRY AIR ENTRAINMENT 
BECOME INCREASINGLY HOSTILE AS 26W APPROACHES THE STRONG UPPER-LEVEL
WESTERLIES AND BEGINS ETT. THE WIND FIELD IS EXPECTED TO REMAIN
EXPANSIVE AT THIS POINT OF TRANSITION.

MODEL DISCUSSION: MODEL TRACK GUIDANCE HAS COME INTO BETTER
AGREEMENT WITH THE EXCEPTION OF THE GFS AND GEFS MEAN LAG BEHIND
IN TRACK SPEED IN COMPARISON TO THE REMAINDER OF PHYSICS AND AI
BASED GUIDANCE OUT TO TAU 96. BETWEEN TAUS 96 AND 120, GUIDANCE
DISAGREES GREATLY ON THE TRACK SPEED OF 26W AS IT COMPLETES ETT,
WITH AN ALONG TRACK SPREAD OF 650 NM AND NO CLEAR DISTINCTION
BETWEEN AI AND PHYSICS-BASED MODELS AS ECMWF AND JGSM OUTPACE THE
AI GFS, AI GFS ENSEMBLE, AND EXPERIMENTAL WINDBORNE WEATHER MESH
ENSEMBLE, BUT REMAIN SLOWER THAN THE GOOGLE DEEPMIND SOLUTION. THE
OFFICIAL JTWC FORECAST TRACK IS THUS LAID WITH HIGH CONFIDENCE OUT
TO TAU 72, IN GOOD AGREEMENT BETWEEN THE MULTI-MODEL AND AI
CONSENSUS, AND WITH LOW CONFIDENCE THEREAFTER DUE TO THE SPREAD IN
TRACK SPEED. INTENSITY GUIDANCE CONTINUES TO AGREE ON AN
INTENSIFICATION OUT TO TAU 48 FOLLOWED BY A GRADUAL WEAKENING, BUT
THERE REMAINS A SPREAD OF 45 KTS AT THIS POINT BETWEEN THE LOWEST
OUTLIER OF GFS-DERIVED COAMPS-TC AND THE RI AID DTOP, WHICH PREDICTS
SUPERTYPHOON INTENSITY AT THIS POINT. THE OFFICIAL JTWC INTENSITY
FORECAST IS ASSESSED WITH MEDIUM CONFIDENCE OUT TO TAU 72, IN GOOD
AGREEMENT WITH THE MULTI-MODEL CONSENSUS AND GOOGLE DEEPMIND, WITH
SOME UNCERTAINTY REMAINING IN THE ULTIMATE PEAK 26W WILL REACH AS
IT UNDERGOES RI. PAST TAU 72, THE INTENSITY FORECAST IS ASSESSED
WITH LOW CONFIDENCE, BELOW THE MULTI-MODEL CONSENSUS DUE TO HIGHER
UNCERTAINTY REGARDING THE EFFECT OF ETT ON THE RATE OF WEAKENING.

FORECAST CONFIDENCE:
   TRACK 00-72 HR: HIGH
   TRACK 72-120 HR: LOW
   INTENSITY 00-72 HR: MEDIUM
   INTENSITY 72-120 HR: LOW//
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