Advisories

WDPN32 PGTW 021500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 26W (CHOI-WAN) WARNING NR 011//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 17.7N 144.6E
   INITIAL INTENSITY: 70 KTS
   GEOGRAPHIC REFERENCE: 165 NM NORTH-NORTHWEST OF SAIPAN
   MOVEMENT PAST 6 HOURS: NORTHWARD AT 08 KTS
   SIGNIFICANT WAVE HEIGHT: 28 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS TYPHOON
(TY) 26W AS A QUICKLY DEVELOPING SYSTEM WITH ROBUST DEEP CONVECTION
AND AN IMPROVING POLEWARD OUTFLOW CHANNEL. THE UPPER-LEVEL
CONVECTION IS STRUGGLING TO MAINTAIN ORGANIZATION, THOUGH IT IS
STILL FIGHTING TO WRAP UPSHEAR. THE LOWER-LEVEL CLOUD BANDING IS
STILL PARTIALLY EXPOSED ALONG THE NORTHWESTERN EDGE OF THE
CIRCULATION. THE 020832Z SAR PASS REVEALED A WIDE SWATH OF
TYPHOON-FORCE WINDS AND A SYMMETRICAL INNER CORE. ENVIRONMENTAL
ANALYSIS REVEALS A HIGHLY FAVORABLE ENVIRONMENT CHARACTERIZED BY LOW
(5-10 KTS) VERTICAL WIND SHEAR (VWS), WARM (29-30 C) SEA SURFACE
TEMPERATURES (SST), HIGH (100-120 KJ PER CM SQUARED) OCEAN HEAT
CONTENT (OHC), AND STRONG DIVERGENCE ALOFT. THE INITIAL POSITION IS
PLACED WITH MEDIUM CONFIDENCE BASED ON LOWER-LEVEL CLOUD BANDING
AND EXTRAPOLATION FROM THE EARLIER 020832Z RCM-3 SAR DATA. THE
INITIAL INTENSITY OF 70 KTS IS ASSESSED WITH HIGH CONFIDENCE ALSO
BASED ON THE SAR DATA. THE CIMSS INTENSITY ESTIMATES ARE ASSESSED
TO BE UNDERESTIMATING THE ACTUAL INTENSITY OF THE STORM.

INITIAL WIND RADII BASIS: 020832Z RCM-3 SAR DATA

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

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T3.5 - 55 KTS
   RJTD: T3.5 - 55 KTS
   RCTP: T3.5 - 55 KTS
   CIMSS ADT: 55 KTS AT 021240Z
   CIMSS AIDT: 46 KTS AT 021240Z
   CIMSS D-MINT: 66 KTS AT 020800Z
   CIMSS D-PRINT: 63 KTS AT 021130Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: HIGHLY FAVORABLE
   VWS: 5-10 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: STRONG EQUATORWARD

ANALYSIS CONFIDENCE:
   INITIAL POSITION: MEDIUM
   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: TY 26W (CHOI-WAN) IS CURRENTLY TRACKING
POLEWARD AS THE STR TO ITS NORTHEAST IS ERODED BY A PASSING
SHORTWAVE TROUGH TO THE NORTH. THE TROUGH WILL CONTINUE TO ERODE
THE WESTERN FLANK OF THE STR THROUGH TAU 36-48, INDUCING A
NORTHEASTWARD TRACK FOR CHOI-WAN. BY TAU 48, THE TROUGH IS EXPECTED
TO HAVE PASSED, AND THE STR IS EXPECTED TO RE-ORIENT AND BUILD
WESTWARD. THIS IS EXPECTED TO CAUSE 26W TO CURVE NORTHWESTWARD
BETWEEN TAU 48-72. JUST AFTER TAU 72, 26W IS ANTICIPATED TO ROUND
THE RIDGE AXIS AND SKIRT THE EDGE OF THE UPPER-LEVEL WESTERLIES.
26W IS FORECAST TO MAINTAIN A NORTHEASTWARD TRACK THROUGH THE END
OF THE FORECAST. THE ENVIRONMENT WILL DETERIORATE DRASTICALLY AS
26W TRACKS FURTHER POLEWARD. CHOI-WAN IS EXPECTED TO CROSS THE 26C
ISOTHERM AROUND TAU 96 AND ENCOUNTER HIGH (30+ KTS) VWS DUE TO THE
PROXIMITY TO THE WESTERLIES, WHICH WILL FORCE HIGH AMOUNTS OF DRY
AIR INTO THE CORE AND INDUCE THERMAL ADVECTION. IN RESPONSE TO THE
HOSTILE ENVIRONMENT, 26W IS FORECAST TO BEGIN EXTRATROPICAL
TRANSITION AT TAU 96 AND COMPLETE TRANSITION NO LATER THAN TAU 120.
REGARDING INTENSITY, 26W IS FORECAST TO UNDERGO A PERIOD OF RAPID
INTENSIFICATION BEGINNING IMMINENTLY AND LASTING THROUGH TAU 24.
WITHIN THE NEXT 12 HOURS, THE ENVIRONMENT WILL BECOME INCREASINGLY 
FAVORABLE, WITH REDUCED VWS OF 10-15 KTS, AN ENHANCED POLEWARD
OUTFLOW CHANNEL PROVIDED BY THE RETREATING STR, AND HIGHER (150+ KJ
PER CM SQUARED) OHC. BY TAU 36, 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 BEGINNING AT TAU 48. THE WEAKENING TREND
WILL BE EXACERBATED BY THE DETERIORATING ENVIRONMENT AS CHOI-WAN
TRACKS POLEWARD. CHOI-WAN IS EXPECTED TO MAINTAIN AN EXPANSIVE WIND
FIELD THROUGH THE DURATION OF THE FORECAST.

MODEL DISCUSSION: DETERMINISTIC MODEL TRACK GUIDANCE IS IN STRONG
AGREEMENT IN THE SHORT-TERM FORECAST, BUT POOR AGREEMENT IN THE
LONG-TERM FORECAST, AS MODEL SOLUTIONS STRUGGLE TO INTERPRET THE
TRACK SPEEDS REGARDING THE RECURVE AND EXTRATROPICAL TRANSITION.
THERE REMAINS A DISTINCT SPEED BIFURCATION BETWEEN THE
PHYSICS-BASED MODELS AND EXPERIMENTAL AI-BASED MODELS. HOWEVER,
SEVERAL PHYSICS-BASED SOLUTIONS ARE NOW IN AGREEMENT WITH THE
AI MODELS, INCLUDING ECMWF AND GSM. THE PRIMARY OUTLIERS ARE GFS
AND GEFS, BOTH OF WHICH DEPICT SIGNIFICANTLY SLOWER TRACK SPEEDS
THAN ANY OTHER MODEL SOLUTION. THE JTWC TRACK FORECAST IS PLACED
NEAR THE PHYSICS-BASED AND AI-BASED MULTI-MODEL CONSENSUS, WITH
HIGH CONFIDENCE FROM TAU 0-72 AND LOW CONFIDENCE FROM TAU 72-120 AS
A RESULT OF THE UNCERTAINTY REGARDING THE MODEL SPREAD AFTER TAU
72. RELIABLE INTENSITY AIDS ARE IN MODERATE AGREEMENT IN
INTENSIFICATION AND WEAKENING TRENDS, BUT DISAGREE ON THE PEAK 
INTENSITY. THE RAPID INTENSIFICATION DETERMINISTIC ENSEMBLE (RIDE)
AND RAPID INTENSIFICATION CONSENSUS HAVE REACHED CRITERIA AND
INDICATE THE POSSIBILITY OF RAPID INTENSIFICATION WITHIN THE NEXT
36 HOURS. GUIDANCE IS IN TIGHT AGREEMENT FROM TAU 0-36, BUT
DIVERGES SIGNIFICANTLY THEREAFTER. INTENSITY GUIDANCE INDICATES A
PEAK INTENSITY BETWEEN 85 KTS (GFS) AND 135 KTS (HAFS-A). FOLLOWING
THE PEAK, INTENSITY GUIDANCE DISAGREES ON THE TREND AS 26W
TRANSITIONS TO AN EXTRATROPICAL SYSTEM, WITH A HANDFUL OF MODELS
INDICATING A BRIEF REINTENSIFICATION PERIOD AROUND TAU 96. THE JTWC
INTENSITY FORECAST LIES IN ALIGNMENT WITH THE MULTI-MODEL CONSENSUS
AND THE EXPERIMENTAL GOOGLE DEEPMIND. THE INTENSITY FORECAST IS
ASSESSED WITH OVERALL MEDIUM CONFIDENCE DUE TO THE UNCERTAINTY
REGARDING PEAK INTENSITY AND EXTRATROPICAL TRANSITION. 

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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