Advisories

WDPN32 PGTW 011500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 26W (CHOI-WAN) WARNING NR 
007//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 16.5N 145.8E
   INITIAL INTENSITY: 50 KTS
   GEOGRAPHIC REFERENCE: 91 NM NORTH OF TINIAN
   MOVEMENT PAST 6 HOURS: WESTWARD AT 10 KTS
   SIGNIFICANT WAVE HEIGHT: 23 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS TROPICAL
STORM (TS) 26W BEGINNING TO TUCK UNDER THE CENTRAL DEEP CONVECTION
AND REDUCING THE VERTICAL TILT. THE UPPER-LEVEL CONVECTION HAS
BEGUN TO FIGHT THE VERTICAL WIND SHEAR AND IS ATTEMPTING TO EXPAND
UPSHEAR. ADDITIONALLY, THE PARTIALLY EXPOSED LOWER-LEVEL CLOUD
BANDING HAS BECOME TIGHTER AND NOTICEABLY MORE SYMMETRICAL. THE
011158Z ASCAT DATA REVEALS A TIGHT, SLIGHTLY OBLONG INNER CORE
SURROUNDED BY A VAST WIND FIELD. A 011358Z SURFACE OBSERVATION FROM
SAIPAN RECORDED 32 KTS SUSTAINED WINDS WITH GUSTS UP TO 50 KTS.
ENVIRONMENTAL ANALYSIS REVEALS A FAVORABLE ENVIRONMENT, CHARACTERIZED 
BY MODERATE TO HIGH (20-25 KTS) VERTICAL WIND SHEAR (VWS), MODERATE 
EQUATORWARD OUTFLOW, WARM (30-31 C) SEA SURFACE TEMPERATURES, AND HIGH 
(125-150 KJ PER CM SQUARED) OCEAN HEAT CONTENT (OHC). THE INITIAL 
POSITION AND INTENSITY ARE PLACED WITH HIGH CONFIDENCE BASED ON THE 
011157Z ASCAT PASS.

INITIAL WIND RADII BASIS: 011157Z ASCAT DATA

CURRENT STEERING MECHANISM: THE SOUTHWESTERN PERIPHERY OF A
SUBTROPICAL RIDGE (STR) CENTERED TO THE NORTHEAST.

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T3.0 - 45 KTS
   RJTD: T2.5 - 35 KTS
   RCTP: T3.0 - 45 KTS
   CIMSS ADT: 34 KTS AT 011240Z
   CIMSS AIDT: 42 KTS AT 011240Z
   CIMSS D-PRINT: 55 KTS AT 011240Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 20-25 KTS
   SST: 30-31 CELSIUS
   OUTFLOW: MODERATE EQUATORWARD

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

3. FORECAST REASONING.

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

FORECAST DISCUSSION: TS 26W (CHOI-WAN) IS FORECAST TO CONTINUE
TRACKING WEST-NORTHWESTWARD FOR THE NEXT 12 HOURS WHILE IT REMAINS
ON THE SOUTHWESTERN PERIPHERY OF THE STEERING STR. AROUND TAU 12, A
SHORTWAVE TROUGH TO THE NORTH WILL PASS, ERODING THE WESTERN FLANK
OF THE RIDGE. IN RESPONSE, 26W WILL SLOWLY CURVE POLEWARD INTO THE
WEAK STEERING ENVIRONMENT CREATED AS THE RIDGE RETREATS EASTWARD.
26W WILL TRACK NORTHWARD TO NORTH-NORTHEASTWARD FROM TAU 24-60 WITH
A NEAR EQUATORIAL RIDGE CENTERED TO THE SOUTHEAST PROVIDING THE
NORTHEASTWARD STEERING INFLUENCE. BEGINNING AROUND TAU 60, THE NOW
RE-ORIENTED STEERING RIDGE WILL BUILD BACK WESTWARD, CAUSING 26W TO
BRIEFLY CURVE NORTHWESTWARD BEFORE ASSUMING A GENERALLY NORTHWARD
TRACK FROM TAU 96-120. REGARDING INTENSITY, 26W IS FORECAST TO 
STEADILY INTENSIFY THROUGH TAU 72. AT AROUND TAU 24, THE ENVIRONMENT 
WILL BECOME MORE FAVORABLE, INCLUDING REDUCED VWS OF 10-15 KTS, AN 
ENHANCED POLEWARD OUTFLOW CHANNEL PROVIDED BY THE RETREATING STR, AND 
HIGH (125-150 KJ PER CM SQUARED) OCEAN HEAT CONTENT (OHC). DUE TO THE 
IMPROVED ENVIRONMENT BETWEEN TAU 24-72, AN INCREASED RATE OF 
INTENSIFICATION MAY BE OBSERVED, INCLUDING THE POTENTIAL FOR RAPID 
INTENSIFICATION AND A PEAK INTENSITY HIGHER THAN 110 KTS. BY TAU 72, 
26W IS FORECAST TO ENTER INTO A REGION OF LOWER OHC (50-75 KJ PER CM 
SQUARED), WHICH IS EXPECTED TO INDUCE A WEAKENING TREND FROM TAU 72-
120. CHOI-WAN IS EXPECTED TO MAINTAIN AN EXPANSIVE WIND FIELD THROUGH 
THE DURATION OF THE FORECAST.

MODEL DISCUSSION: DETERMINISTIC MODEL TRACK GUIDANCE IS IN GOOD 
AGREEMENT THROUGH TAU 72, WITH BOTH PHYSICS-BASED AND EXPERIMENTAL AI-
BASED SOLUTIONS NOW INDICATING VERY SIMILAR TRACKS. AFTER TAU 72, THE 
PHYSICS-BASED MODELS DEPICT 26W TRACKING DISTINCTLY NORTHWESTWARD 
WHILE THE AI-BASED MODELS DEPICT A NEARLY DUE NORTHWARD TRACK. THE 
JTWC TRACK FORECAST IS PLACED IN ALIGNMENT WITH THE CLOSELY CLUSTERED 
AI-BASED MODELS DUE TO THE HISTORICAL HIGH ACCURACY OF THOSE MODELS. 
ADDITIONALLY, THE JTWC TRACK FORECAST IS PLACED WITH HIGH CONFIDENCE 
FROM TAU 0-72 AND MEDIUM CONFIDENCE FROM TAU 72-120 AS A RESULT OF THE 
UNCERTAINTY REGARDING THE MODEL SPREAD AND TRACK DIRECTION AFTER TAU 
72. RELIABLE INTENSITY AIDS ARE IN MODERATE AGREEMENT IN 
INTENSIFICATION AND WEAKENING TRENDS, BUT DISAGREE ON THE PEAK 
INTENSITY. SEVERAL JTWC RAPID INTENSIFICATION AIDS HAVE REACHED 
CRITERIA, INDICATING THE POSSIBILITY OF RAPID INTENSIFICATION WITHIN 
THE NEXT 48 HOURS. THIS SCENARIO IS DEEMED UNLIKELY BETWEEN TAU 0-24, 
BUT IT IS POSSIBILITY BETWEEN TAU 24-48 AFTER 26W FURTHER CONSOLIDATES 
AND THE ENVIRONMENT IMPROVES. INTENSITY GUIDANCE INDICATES A PEAK 
INTENSITY BETWEEN 85 KTS (COAMPS-TC) AND 120 KTS (RIDE AND FRIA). THE 
JTWC INTENSITY FORECAST IS IN ALIGNMENT WITH PREVIOUS FORECASTS, THE
MULTI-MODEL CONSENSUS, HAFS-A SOLUTION, AND THE EXPERIMENTAL GOOGLE
DEEPMIND. THE JTWC INTENSITY FORECAST IS ASSESSED WITH OVERALL
MEDIUM CONFIDENCE.

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