Advisories

WDPN31 PGTW 260300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 25W (SURIGAE) WARNING NR 
012//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 22.4N 127.0E
   INITIAL INTENSITY: 60 KTS
   GEOGRAPHIC REFERENCE: 250 NM SOUTH OF KADENA AB
   MOVEMENT PAST 6 HOURS: NORTHWESTWARD AT 07 KTS
   SIGNIFICANT WAVE HEIGHT: 22 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS RAPIDLY
CONSOLIDATING DEEP CENTRAL CONVECTION SURROUNDING THE INCREASINGLY
SYMMETRIC AND COMPACT CORE OF TROPICAL STORM (TS) 25W. THE VIGOROUS
CONVECTION AROUND THE CORE RESEMBLES A NASCENT RAGGED EYE THAT IS
STILL MOSTLY CLOUD-FILLED. A 252121Z WSFM MWI 37 GHZ MICROWAVE
IMAGE BOASTS A FULLY DEVELOPED MICROWAVE EYE IN THE LOWER LEVEL.
THE TRACK SPEED HAS SLOWED NOTICEABLY OVER THE PAST 6 HOURS AS THE
SYSTEM CONSOLIDATES AND APPROACHES THE AXIS OF THE STEERING RIDGE.
A 252127Z SENTINEL-1C SAR IMAGE REVEALED IMPROVED SYMMETRY OF THE
SURROUNDING WIND FIELD AND A MEAN VMAX OF 61 KTS. THE INITIAL
POSITION IS PLACED WITH MEDIUM CONFIDENCE BASED ON THE CENTER OF
THE ROTATING CONVECTION IN ANIMATED MSI AND EXTRAPOLATION FROM THE
EARLIER MICROWAVE IMAGERY. THE INITIAL INTENSITY OF 60 KTS IS
ASSESSED WITH MEDIUM CONFIDENCE BASED ON THE LARGE SPREAD OF AGENCY
DVORAK FIXES AND CIMSS OBJECTIVE INTENSITY GUIDANCE, BUOYED BY THE
SAR DATA. THE ENVIRONMENT IS CHARACTERIZED AS FAVORABLE WITH WARM
SEA SURFACE TEMPERATURES, LOW VERTICAL WIND SHEAR (VWS), AND
EXCELLENT OUTFLOW ALOFT.

INITIAL WIND RADII BASIS: PERSISTENCE 

CURRENT STEERING MECHANISM: WESTERN FLANK OF A SUBTROPICAL RIDGE
(STR) CENTERED SOUTH OF HONSHU

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T4.0 - 65 KTS
   RJTD: T3.0 - 45 KTS
   RCTP: T3.0 - 45 KTS
   CIMSS SATCON: 56 KTS AT 260010Z
   CIMSS ADT: 47 KTS AT 260010Z
   CIMSS AIDT: 46 KTS AT 260010Z
   CIMSS D-MINT: 67 KTS AT 260036Z
   CIMSS D-PRINT: 55 KTS AT 260010Z

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

ANALYSIS CONFIDENCE:
   INITIAL POSITION: MEDIUM
   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: THE TRACK SPEED OF TS 25W HAS SLOWED FURTHER
OVER THE PAST 6 HOURS AS THE SYSTEM APPROACHES THE AXIS OF THE
STEERING RIDGE CENTERED TO THE EAST. THE TRACK IS FORECAST TO
REMAIN SLOW OVER THE NEXT 24 HOURS AS 25W ROUNDS THE RIDGE AXIS,
TURNING POLEWARD AND THEN NORTHEASTWARD. THE TRAJECTORY GRADUALLY
ACCELERATES NORTHEASTWARD THROUGH TAU 72 UNDER A WEAKER STEERING
GRADIENT, TRACKING ROUGHLY PARALLEL TO THE RYUKYU ISLANDS. AFTER
TAU 72, THE SYSTEM MAINTAINS AN ACCELERATED EAST-NORTHEASTWARD
TRACK AS IT APPROACHES THE MID-LATITUDE BAROCLINIC ZONE. THE
INTENSITY FORECAST CALLS FOR A PERIOD OF STEADY INTENSIFICATION
OVER THE NEXT 24 HOURS, JUST SHY OF RAPID INTENSIFICATION (RI),
ALTHOUGH RI REMAINS A POSSIBILITY. AFTER THE INTENSITY PLATEAUS
AROUND 85 KTS BETWEEN TAU 24-36, A GRADUAL WEAKENING TREND IS
EXPECTED DUE TO DECREASING SEA SURFACE TEMPERATURES AND INCREASING
VWS. ALTHOUGH THE INTENSITY IS EXPECTED TO EXCEED TROPICAL STORM
FORCE AT TAU 120, THE SYSTEM IS EXPECTED TO BECOME EMBEDDED IN THE
MID-LATITUDE BAROCLINIC ZONE AND BEGIN EXTRATROPICAL TRANSITION.   

MODEL DISCUSSION: MODEL TRACK GUIDANCE IS IN GOOD AGREEMENT ABOUT
THE RECURVING SCENARIO BUT THERE IS STILL A SIGNIFICANT DISCREPANCY
IN THE TRACK SPEED. THE NOTABLE OUTLIERS THAT HAVE A MUCH SLOWER
TRACK SPEED AND EVENTUAL QUASI-STATIONARY POSITION AROUND THE
SOUTHERN RYUKYUS INCLUDE THE GFS DETERMINISTIC AND JGSM MODELS. THE
REMAINDER OF DYNAMIC MODELS (INCLUDING ECMWF SOLUTIONS, NAVGEM,
UKMET, AND GFS ENSEMBLE MEAN) DEPICT A RANGE OF MORE TYPICAL
RECURVING TRACK SPEEDS. FURTHER, THE PREPONDERANCE OPERATIONAL AND
EXPERIMENTAL AI MODELS (INCLUDING GOOGLE DEEPMIND) DEPICT A MUCH
FASTER RECURVING SCENARIO. THE JTWC TRACK FORECAST IS PLACED NEAR
THE CONSENSUS OF AI MODELS, WHICH IS A BIT FASTER THAN THE DYNAMIC
MODELS (EXCEPTING THE OUTLIERS) AND A BIT SLOWER THAN THE MOST
AGGRESSIVE AI SOLUTIONS. THE INTENSITY GUIDANCE PACKAGE INCLUDED
SEVERAL RI AIDS IN THE LATEST MODEL RUN, WHICH SUGGEST THE
POSSIBILITY OF RI IN THE NEXT 24 HOURS THOUGH THAT IS NOT
EXPLICITLY FORECAST. THE REST OF THE INTENSITY GUIDANCE VARIES
WIDELY DEPENDING ON THE TRACK FORECAST OF THE GUIDANCE MODEL. THE
JTWC INTENSITY FORECAST DISCOUNTS THE GUIDANCE THAT RESULTS FROM
THE NON-RECURVING SCENARIO AND ALIGNS CLOSER TO AVAILABLE AI
GUIDANCE THAT DEPICTS A MORE REALISTIC RECURVING SCENARIO. ALL OF
THAT SAID, THE PERSISTENCE OF GFS AND ITS DERIVATIVE SOLUTIONS IN
DEPICTING AN EVENTUAL QUASI-STATIONARY POSITION CANNOT BE IGNORED
AS AN OUTSIDE POSSIBILITY, DESPITE THE CURRENT OFFICIAL FORECAST
NOT REPRESENTING IT.

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