Advisories

WDPN32 PGTW 302100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 26W (CHOI-WAN) WARNING NR 
004//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 16.2N 150.0E
   INITIAL INTENSITY: 35 KTS
   GEOGRAPHIC REFERENCE: 331 NM EAST-NORTHEAST OF ANDERSEN AFB
   MOVEMENT PAST 6 HOURS: WEST-NORTHWESTWARD AT 08 KTS
   SIGNIFICANT WAVE HEIGHT: 15 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
TROPICAL STORM (TS) 26W IS GRADUALLY INTENSIFYING. ANIMATED
ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS CURVED BANDING
DISPLACED WEST OF A PARTIALLY OBSCURED, ELONGATED LOW-LEVEL
CIRCULATION CENTER (LLCC). THE ASSOCIATED CONVECTION IS
PARTICULARLY DEEP, WITH CLOUD TOP TEMPERATURES AS COLD AS -90
DEGREES CELSIUS, WHILE THE CURVATURE OF THE CONVECTIVE BANDING
CONTINUES TO IMPROVE. A 301448Z AMSR3 PASS INDICATES THAT THE
VORTEX IS TILTED WESTWARD WITH HEIGHT. THIS STRUCTURE IS CONSISTENT
WITH EASTERLY MID-LEVEL SHEAR OF NEAR 20 KTS, WHICH IS PREVENTING
THE SYSTEM FROM BECOMING VERTICALLY ALIGNED. DESPITE THE SHEAR, THE
ENVIRONMENT IS FAVORABLE, CHARACTERIZED BY VERY WARM SEA SURFACE
TEMPERATURES (SST) OF 30 DEGREES CELSIUS AND VERY HIGH OHC NEAR 140
KJ PER CM2, MODERATE RADIAL OUTFLOW ALOFT, AND PLENTIFUL DEEP-LAYER
MOISTURE. THE INITIAL POSITION IS PLACED WITH LOW CONFIDENCE,
HEDGED EAST OF THE MID-LEVEL CIRCULATION CENTER TO ACCOUNT FOR
VORTEX TILT. AN AGED 301015Z ASCAT-B PASS REVEALED A COMPACT PATCH
OF GALE-FORCE WINDS ISOLATED TO THE NORTHWEST QUADRANT, EMBEDDED
WITHIN A MUCH BROADER 20- TO 25-KT WIND FIELD ACROSS THE REMAINING
QUADRANTS. GIVEN THE GAP SINCE THAT PASS AND SUBSEQUENT
CONSOLIDATION, IT REMAINS UNCERTAIN WHETHER THE OBSERVED STRUCTURAL
IMPROVEMENT HAS ONLY EXPANDED THE AREAL FOOTPRINT OF GALES OR ALSO
INCREASED THE MAXIMUM SUSTAINED WINDS. ACCORDINGLY, THE INITIAL
INTENSITY HAS BEEN HELD AT 35 KTS WITH MEDIUM CONFIDENCE, SUPPORTED
BY AIDT AND THE T2.5 DVORAK ESTIMATE FROM PGTW.

INITIAL WIND RADII BASIS: SCATTEROMETER DATA 

CURRENT STEERING MECHANISM: SOUTHERN PERIPHERY OF A LOW- TO
MID-LEVEL SUBTROPICAL RIDGE CENTERED FAR TO THE NORTHEAST

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T2.5 - 35 KTS
   RJTD: T1.5 - 25 KTS
   RCTP: T2.0 - 30 KTS
   CIMSS ADT: 41 KTS AT 301430Z
   CIMSS AIDT: 35 KTS AT 301430Z
   CIMSS D-MINT: 26 KTS AT 301540Z
   CIMSS D-PRINT: 30 KTS AT 301710Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 15-20 KTS
   SST: 30-31 CELSIUS
   OUTFLOW: MODERATE RADIAL

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

3. FORECAST REASONING.

SIGNIFICANT FORECAST CHANGES: THE FORECAST WIND RADII HAVE BEEN
SIGNIFICANTLY EXPANDED BEYOND TAU 48.

FORECAST DISCUSSION: TS 26W IS MOVING WEST-NORTHWESTWARD ALONG THE
SOUTHERN PERIPHERY OF A LOW- TO MID-LEVEL STR CENTERED NEAR 31N
169E. THIS MOTION WILL CONTINUE FOR THE NEXT 24 HOURS. AFTER THAT
TIME, A PROGRESSIVE SHORTWAVE TROUGH RACING DOWNSTREAM OF NORTHERN
HONSHU AND HOKKAIDO WILL ERODE THE STR. THE PRIMARY STEERING
INFLUENCE WILL WEAKEN MARKEDLY, AND TS 26W WILL BECOME NEARLY
STATIONARY. THE SYSTEM WILL THEN TURN POLEWARD NEAR TAU 36 AS THE
DEEP-LAYER STR REORIENTS, AND THE WESTERN FLANK OF THE RIDGE
BECOMES THE DOMINANT STEERING MECHANISM. TOWARD THE END OF THE
FORECAST PERIOD, THE TRAJECTORY WILL NUDGE WESTWARD AS THE RIDGE
BUILDS SLIGHTLY WESTWARD. THE FORECAST CALLS FOR GRADUAL TO STEADY
INTENSIFICATION FOR THE FIRST 24 HOURS, GIVING TIME FOR THE STORM
TO BECOME VERTICALLY ALIGNED AND MORE SYMMETRIC. AFTER TAU 24, THE
PERSISTENT MID-LEVEL SHEAR WILL EASE. COUPLED WITH VERY WARM SST
AND VERY HIGH OHC, THE LOWER SHEAR AND RICH DEEP-LAYER MOISTURE
WILL ENABLE TS 26W TO UNDERGO SIGNIFICANT INTENSIFICATION. BETWEEN
TAU 72 AND TAU 96, THE SYSTEM WILL MOVE OVER LOWER OHC, WHICH WILL
LIMIT CONTINUED INTENSIFICATION. THE PROGRESSIVELY COOLER SST AND
LOWER OHC WILL BECOME INCREASINGLY UNFAVORABLE FOR MAINTAINING PEAK
INTENSITY, LEADING TO GRADUAL WEAKENING AFTER TAU 96. THE LOW-LEVEL
CIRCULATION ASSOCIATED WITH TS 26W IS LARGE. THE WIND FIELD WILL
EXPAND THROUGH THE MAJORITY OF THE FORECAST PERIOD, WITH IMPACTS
EXTENDING FAR FROM THE CENTER.

MODEL DISCUSSION: THE JTWC FORECAST TRACK HAS CHANGED VERY LITTLE
THIS CYCLE. TRACK GUIDANCE IS COMING INTO BETTER AGREEMENT ON THE
LOCATION AND TIMING OF THE POLEWARD TURN, WITH DYNAMICAL MODELS
GENERALLY SHIFTING WESTWARD AND THE AI MODELS SHIFTING EASTWARD
TOWARD A COMMON SOLUTION. AT THE POINT OF RECURVATURE, THE SPATIAL
SPREAD AMONG THE GUIDANCE IS APPROXIMATELY 125 NM. NAVGEM AND
HAFS-A ARE FASTEST IN DEPICTING THE POLEWARD TURN, LIKELY
ATTRIBUTED TO THEIR TENDENCY TO SIMULATE STRONGER CONVECTIVE
FEEDBACKS. ECMWF AND GOOGLE DEEPMIND ARE THE WESTERNMOST SOLUTIONS,
DELAYING THE TURN BY 6-12 HOURS RELATIVE TO THE AI CONSENSUS. THE
FORECAST TRACK IS POSITIONED NEAR THE MEAN OF THE AI MODELS THROUGH
TAU 120 WITH MEDIUM CONFIDENCE, WHICH IS NOW ONLY 50 NM WEST OF THE
JTWC CONSENSUS TRACKER (CONW) AT TAU 60. SUBSEQUENT FORECASTS
RETAIN SOME FLEXIBILITY TO SHIFT THE TRACK SLIGHTLY FARTHER SOUTH
AND WEST BEFORE THE SHARP POLEWARD TURN. MULTIPLE RAPID
INTENSIFICATION (RI) AIDS HAVE TRIGGERED THIS CYCLE. SHIPS
INDICATES A 48 PERCENT PROBABILITY OF A 65-KT INCREASE IN THE NEXT
72 HOURS. GOOGLE DEEPMIND ALSO PREDICTS SIGNIFICANT
INTENSIFICATION. GIVEN THE MODEL SUPPORT AND FAVORABLE ENVIRONMENT
AHEAD OF THE STORM, THE FORECAST CALLS FOR RI TO COMMENCE AFTER TAU
24. THE JTWC INTENSITY FORECAST IS SET AT THE UPPER END OF THE
GUIDANCE ENVELOPE WITH MEDIUM CONFIDENCE, LYING CLOSEST TO THE
DEEPMIND SOLUTION.

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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