Advisories

WDPN32 PGTW 010900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 26W (CHOI-WAN) WARNING NR 
006//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 16.9N 146.8E
   INITIAL INTENSITY: 40 KTS
   GEOGRAPHIC REFERENCE: 133 NM NORTH-NORTHEAST OF TINIAN
   MOVEMENT PAST 6 HOURS: WESTWARD AT 11 KTS
   SIGNIFICANT WAVE HEIGHT: 20 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS TROPICAL
STORM (TS) 26W AS AN ELONGATED AND PARTIALLY EXPOSED LOW LEVEL
CIRCULATION CENTER (LLCC). THE NORTHEASTERN QUADRANT OF THE LLCC IS
NEARLY FULLY EXPOSED, AS THE DEEP CONVECTION IS SHEARED TO THE
SOUTHWEST BY MODERATE TO HIGH (20-25 KTS) VERTICAL WIND SHEAR
(VWS). THE DEEP CONVECTION IS FAILING TO WRAP TO THE UPSHEAR SIDE
OF THE SYSTEM, INDICATING THAT DEVELOPMENT HAS MOMENTARILY STALLED.
ADDITIONALLY, THE VWS IS DISPLACING THE MID-LEVEL CENTER AND
INDUCING A SOUTHWESTWARD TILT WITH HEIGHT, ALSO INHIBITING
DEVELOPMENT. ENVIRONMENTAL ANALYSIS REVEALS A MARGINALLY FAVORABLE
ENVIRONMENT, CHARACTERIZED BY WARM (30-31 C) SEA SURFACE
TEMPERATURES (SST) AND MODERATE EQUATORWARD OUTFLOW, OFFSET BY VWS.
SURFACE OBSERVATIONS FROM SAIPAN REPORT SUSTAINED WINDS OF 22 KTS
AND GUSTING TO 33 KTS AT 010733Z. JUST TO THE SOUTHWEST, SURFACE
OBSERVATIONS FROM TINIAN REPORTED 18 KTS GUSTING TO 26 KTS AT
010656Z.

INITIAL WIND RADII BASIS: PERSISTENCE 

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: T2.5 - 35 KTS
   CIMSS SATCON: 42 KTS AT 010610Z
   CIMSS ADT: 34 KTS AT 010640Z
   CIMSS AIDT: 41 KTS AT 010640Z
   CIMSS D-MINT: 39 KTS AT 010345Z
   CIMSS D-PRINT: 39 KTS AT 010540Z

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

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 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
12-24, A SHORTWAVE TROUGH TO THE NORTH WILL PASS, ERODING THE
WESTERN FLANK OF THE RIDGE. IN RESPONSE, 26W WILL CURVE POLEWARD
INTO THE WEAK STEERING ENVIRONMENT CREATED AS THE RIDGE RETREATS
EASTWARD. 26W WILL TRACK NORTHWARD TO NORTH-NORTHEASTWARD FROM TAU
36-72 WITH A NEAR EQUATORIAL RIDGE CENTERED TO THE SOUTHEAST
PROVIDING THE NORTHEASTWARD STEERING INFLUENCE. BEGINNING AROUND
TAU 72, 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 GRADUALLY INTENSIFY THROUGH TAU 24.
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). AS A RESULT, CHOI-WAN IS
FORECAST TO INTENSIFY AT A STEADY RATE FROM TAU 24-72. 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 POOR
AGREEMENT THROUGHOUT THE FORECAST PERIOD. THERE IS A DISTINCT SPLIT
BETWEEN THE PHYSICS-BASED MODELS AND THE EXPERIMENTAL AI-BASED
MODELS, PARTICULARLY REGARDING THE TIMING AND SPEED OF THE POLEWARD
RECURVE. PHYSICS-BASED MODELS HAVE A CROSS-TRACK SPREAD OF 150 NM
AT THE WIDEST AT TAU 72, BUT MINIMAL ALONG-TRACK SPREAD.
CONVERSELY, AI-BASED MODELS BOAST A CROSS-TRACK SPREAD OF LESS THAN
90 NM AND MINIMAL ALONG-TRACK SPREAD FOR THE DURATION OF THE
FORECAST. THE TIGHT ENVELOPE OF THE AI-BASED MODELS ALSO COINCIDES
WITH THE MOST RELIABLE PHYSICS-BASED MODEL SOLUTIONS THROUGH TAU
60, INCLUDING GFS AND ECMWF. AFTER TAU 60, 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 AI-BASED MODELS DUE TO THE
HISTORICAL HIGH ACCURACY OF THOSE MODELS. ADDITIONALLY, THE JTWC
TRACK FORECAST IS PLACED WITH OVERALL MEDIUM CONFIDENCE AS A RESULT
OF THE UNCERTAINTY REGARDING THE TIMING OF THE RECURVE AND THE
MODEL SPREAD. 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, BUT NOT
IMPOSSIBLE, GIVEN THE CURRENT STORM STRUCTURE. INTENSITY GUIDANCE
INDICATES A PEAK INTENSITY BETWEEN 85 KTD (HAFS-A) AND 110 KTS
(RIDE). THE JTWC INTENSITY FORECAST IS IN ALIGNMENT WITH PREVIOUS
FORECASTS AND THE EXPERIMENTAL GOOGLE DEEPMIND AND IS ASSESSED WITH
OVERALL MEDIUM CONFIDENCE. 

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