Advisories

WDPN32 PGTW 020300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 26W (CHOI-WAN) WARNING NR 
009//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 17.0N 144.7E
   INITIAL INTENSITY: 55 KTS
   GEOGRAPHIC REFERENCE: 68 NM WEST-NORTHWEST OF ANATAHAN
   MOVEMENT PAST 6 HOURS: WEST-NORTHWESTWARD AT 04 KTS
   SIGNIFICANT WAVE HEIGHT: 25 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS TROPICAL
STORM (TS) 26W (CHOI-WAN) IMPROVING IN STRUCTURE WITH A MORE
SYMMETRICAL AND PARTIALLY OBSCURED LOW LEVEL CIRCULATION CENTER 
(LLCC). VORTEX PRECESSION HAS CAUSED THE UPPER LEVEL CIRCULATION TO 
ORBIT AROUND THE LLCC, WITH THE CDO CURRENTLY DISPLACED TO THE 
SOUTHEAST. 26W DOES SEEM TO BE VERTICALLY ALIGNING, AS EVIDENCED IN A
012158Z GPM MICROWAVE PASS WHICH DEPICTS A PARTIAL MICROWAVE EYE
FEATURE IN THE 36 GHZ IMAGE, WITH THE UPPER-LEVEL CIRCULATION 
REFLECTED IN THE 89 GHZ IMAGE ONLY SLIGHTLY DISPLACED TO THE 
SOUTHEAST. THE MICROWAVE DATA ALSO DEPICTS A WELL-DEFINED CONVECTIVE 
BAND EXTENDING TO THE SOUTHWEST FROM THE LLCC, WHILE 26W STILL LACKS 
ANY STRONG CONVECTION WRAPPING AROUND ON THE NORTHERN SEMICIRCLE.
ENVIRONMENTAL CONDITIONS ARE ASSESSED AS FAVORABLE, WITH LOW TO
MODERATE (15-20 KTS) OF VERTICAL WIND SHEAR, WARM (29-30 C) SEA
SURFACE TEMPERATURES, AND STRONG EQUATORWARD OUTFLOW ALOFT. THE
INITIAL POSITION IS PLACED WITH HIGH CONFIDENCE BASED ON THE
MICROWAVE AND MSI IMAGERY. THE INITIAL INTENSITY IS ASSESSED WITH
MEDIUM CONFIDENCE, MORE IN LINE WITH AGENCY DVORAK FIXES AND ABOVE
THE MAJORITY OF CIMSS OBJECTIVE ESTIMATES, SUPPORTED BY SURFACE
OBSERVATIONS OF 30-35 KTS FROM ACROSS THE MARIANA ISLANDS.

INITIAL WIND RADII BASIS: PERSISTENCE 

CURRENT STEERING MECHANISM: THE WESTERN EXTENSION OF A SUBTROPICAL 
RIDGE CENTERED TO THE NORTHEAST

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T3.5 - 55 KTS
   RJTD: T2.5 - 35 KTS
   RCTP: T3.5 - 55 KTS
   PHFO: T3.0 - 45 KTS
   CIMSS SATCON: 52 KTS AT 011959Z
   CIMSS ADT: 43 KTS AT 012340Z
   CIMSS AIDT: 41 KTS AT 012310Z
   CIMSS D-MINT: 50 KTS AT 012113Z
   CIMSS D-PRINT: 45 KTS AT 012310Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 15-20 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: STRONG EQUATORWARD

ANALYSIS CONFIDENCE:
   INITIAL POSITION: HIGH
   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: TS 26W HAS SLOWED IN TRACK SPEED AND BEGUN A
POLEWARD TURN AS IT ENTERS AN AREA OF WEAKER STEERING INFLUENCE AS
A SHORTWAVE TROUGH TO THE NORTH PROPAGATES EASTWARD, WEAKENING THE
WESTERN EXTENSION OF THE SUBTROPICAL RIDGE (STR) CENTERED TO THE
NORTHEAST. OUT TO TAU 24, 26W WILL BE PRIMARILY STEERED
NORTH-NORTHEASTWARD BY THE NEAR-EQUATORIAL RIDGE (NER) CENTERED TO
THE SOUTHEAST. BY TAU 24, THE STR TO THE NORTHEAST IS EXPECTED TO 
REORIENT AND REGAIN STEERING INFLUENCE, CAUSING AN INCREASE IN TRACK 
SPEED AND A SLIGHT NORTH-NORTHWESTWARD TRACK BETWEEN TAUS 48 AND 96, 
AFTER WHICH POINT 26W IS EXPECTED TO BEGIN RECURVING THE STR AND TURN
NORTHEASTWARD, ACCELERATING ONCE POLEWARD OF THE STR AXIS. REGARDING 
INTENSITY, 26W IS FORECAST TO CONTINUE INTENSIFYING OUT TO A PEAK OF 
105 KTS BETWEEN TAUS 48 AND 60, WITH A PERIOD OF RAPID INTENSIFICATION 
(RI) EXPLICITLY FORECAST FROM TAU 12 TO 36 AS 26W GAINS A POLEWARD 
OUTFLOW CHANNEL AND VWS CONTINUES TO ABATE. AFTER TAU 60, 26W IS 
EXPECTED TO GRADUALLY WEAKEN FOR THE REMAINDER OF THE FORECAST PERIOD 
AS IT ENTERS AN AREA OF LOWER OCEAN HEAT CONTENT OF LESS THAN 100 KJ 
PER CM SQUARED AND  OUTFLOW DECREASES. 

MODEL DISCUSSION: MODEL GUIDANCE REMAINS IN GENERALLY GOOD
AGREEMENT ON THE OVERALL SHAPE OF THE TRACK OF 26W AS IT TRACKS
POLEWARD WITH ALL GUIDANCE DEPICTING AN INITIALLY NORTH-NORTHEASTWARD 
TRACK FOLLOWED BY A NORTH-NORTHWESTWARD TURN AND A NORTHEASTWARD 
RECURVE BY TAU 96 UNDER THE STEERING SCENARIO DESCRIBED ABOVE. 
HOWEVER, THERE IS A INCREASING SPREAD IN TRACK SPEED AS A MAJORITY OF 
AI GUIDANCE CONTINUES TO ACCELERATE 26W AHEAD OF PHYSICS-BASED MODELS 
BEGINNING AT TAU 72, CAUSING AN ALONG TRACK SPREAD OF 700 NM BY TAU 
120 BETWEEN THE FASTEST GUIDANCE OF THE AIFS DETERMINISTIC AND THE 
SLOWEST, GFS ENSEMBLE MEAN. THE OFFICIAL JTWC FORECAST TRACK IS THUS 
LAID WITH MEDIUM CONFIDENCE OUT TO TAU 72, IN BETWEEN THE MULTI-MODEL 
CONSENSUS AND AI CONSENSUS, AND LOW CONFIDENCE THEREAFTER, HEDGING THE 
TRACK AND TRACK SPEED IN BETWEEN THE DIVERGING MULTI-MODEL AND AI
CONSENSUS. INTENSITY GUIDANCE REMAINS IN GOOD AGREEMENT ON
INTENSIFICATION OUT TO TAU 60 AND GRADUAL WEAKENING THEREAFTER,
WITH SEVERAL RI AIDS CONTINUING TO POPULATE. THE MAIN OUTLIERS ARE
THE GFS AND GFS-DERIVED COAMPS-TC SOLUTIONS, WHICH LIE ON THE LOWER
END OF GUIDANCE, LIKELY DUE TO THE ASSOCIATED SLOWER TRACK SPEED OF
THE GFS DETERMINISTIC SOLUTION. THE OFFICIAL JTWC INTENSITY FORECAST 
IS ASSESSED WITH MEDIUM CONFIDENCE FOR THE ENTIRETY OF THE FORECAST 
PERIOD, CLOSELY IN LINE WITH THE MULTI-MODEL CONSENSUS AND GOOGLE 
DEEPMIND. 

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