Advisories

WDPN31 PGTW 250300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 25W (SURIGAE) WARNING NR 
008//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 19.9N 130.7E
   INITIAL INTENSITY: 40 KTS
   GEOGRAPHIC REFERENCE: 427 NM SOUTH-SOUTHEAST OF KADENA AB
   MOVEMENT PAST 6 HOURS: NORTHWESTWARD AT 11 KTS
   SIGNIFICANT WAVE HEIGHT: 16 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS THE LOW-LEVEL 
CIRCULATION CENTER OF TROPICAL STORM (TS) 25W REALIGNING WITH THE DEEP 
CONVECTION THAT WAS PREVIOUSLY DISPLACED TO THE NORTHWEST. THE DEEP 
CONVECTION HAS BEGUN TO PERSIST AROUND THE NORTHERN AND EASTERN 
PERIPHERIES OF THE CORE AS THE VORTEX COMES INTO BETTER ALIGNMENT. 
ANIMATED WATER VAPOR IMAGERY REVEALS THAT POLEWARD OUTFLOW HAS ALSO 
MODESTLY IMPROVED OVER THE PAST 6 HOURS. THE INITIAL POSITION IS 
PLACED WITH MEDIUM CONFIDENCE BASED ON TRACING LOW-LEVEL CLOUD LINES 
JUST UNDER THE OBSCURING CONVECTION IN THE ANIMATED MSI. THE INITIAL 
INTENSITY OF 40 KTS IS ASSESSED WITH MEDIUM CONFIDENCE BASED ON A 
BLEND OF THE AGENCY DVORAK FIXES AND CIMSS OBJECTIVE INTENSITY 
ESTIMATES. THE ENVIRONMENT IS CHARACTERIZED AS FAVORABLE, WITH WARM 
SEA SURFACE TEMPERATURES, LOW VERTICAL WIND SHEAR (VWS), AND GOOD 
OUTFLOW ALOFT. RELATIVELY LOW MID-LEVEL MOISTURE CONTENT IN THE 
SURROUNDING AIR MASS IS THE ONLY MITIGATING ENVIRONMENTAL FACTOR NOW 
THAT VWS HAS BEGUN TO DROP OFF.

INITIAL WIND RADII BASIS: PERSISTENCE 

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

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T3.0 - 45 KTS
   RJTD: T2.5 - 35 KTS
   RCTP: T3.0 - 45 KTS
   CIMSS ADT: 41 KTS AT 242350Z
   CIMSS AIDT: 37 KTS AT 242350Z
   CIMSS D-MINT: 41 KTS AT 242230Z
   CIMSS D-PRINT: 38 KTS AT 242350Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 10-15 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: MODERATE POLEWARD

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 25W HAS CONTINUED ON A NORTHWESTWARD TRACK 
OVER THE PAST 6 HOURS UNDER THE STEERING INFLUENCE OF THE STR CENTERED 
TO THE NORTHEAST. THE NORTHWESTWARD TRAJECTORY IS FORECAST TO CONTINUE 
OVER THE NEXT 24 HOURS ALONG THE SOUTHWESTERN FLANK OF THE STEERING 
RIDGE. AFTER TAU 24, TS 25W WILL APPROACH THE RIDGE AXIS AND TURN 
POLEWARD BEFORE SETTLING INTO A NORTHEASTWARD TRAJECTORY AT A SLOWER 
TRACK SPEED BY TAU 72. THE JTWC FORECAST CALLS FOR A NOTABLE 
ACCELERATION IN TRACK SPEED AFTER TAU 72 AS THE SYSTEM APPROACHES THE 
MID-LATITUDE WESTERLIES. THERE REMAINS UNCERTAINTY ABOUT THE TRACK 
SPEED AFTER TAU 48 DUE TO THE POTENTIAL FOR A SEPARATE STR TO BUILD 
EASTWARD FROM SOUTHEASTERN CHINA, WHICH MAY COMPLICATE THE STEERING 
ENVIRONMENT. THE INTENSITY FORECAST IS TIGHTLY COUPLED TO THE TRACK 
FORECAST IN THIS CASE, INTRODUCING UNCERTAINTY TO THAT ASPECT AS WELL. 
BASED ON WHAT IS ASSESSED TO BE THE MOST LIKELY TRACK, THE INTENSITY 
IS FORECAST STEADILY INCREASE OVER THE NEXT 24 HOURS AS THE SYSTEM 
CONTINUES TO CONSOLIDATE. AFTER TAU 24, A PERIOD OF RAPID 
INTENSIFICATION IS EXPECTED UNDER FAVORABLE ENVIRONMENTAL CONDITIONS, 
WITH AN EXPECTED PEAK INTENSITY OF 85 KTS AROUND TAU 60. GRADUAL 
WEAKENING IS FORECAST FOLLOWING THE SYSTEM'S RECURVE AROUND THE RIDGE 
AXIS AS 25W ACCELERATES TOWARD THE MID-LATITUDES WITH DECREASING SEA 
SURFACE TEMPERATURES AND INCREASING VWS.

MODEL DISCUSSION: MODEL TRACK GUIDANCE REMAINS DIVIDED, WITH MOST 
PHYSICS-BASED MODELS (WITH THE EXCEPTION OF ECMWF) DEPICTING A VERY
SLOW TRACK SPEED THAT BECOMES QUASI-STATIONARY NEAR THE RYUKYU ISLANDS 
BY TAU 120. THE ALTERNATIVE GROUP CONSISTS OF MOST AI-BASED MODELS AND 
THE ECMWF DETERMINISTIC SOLUTION, WHICH DEPICT A MORE TYPICAL TRACK 
SPEED DURING THE RECURVE AND ACCELERATION TOWARD THE MID-LATITUDES. 
OVER THE PAST FEW DAYS, GUIDANCE HAS TRENDED TOWARD FAVORING THE 
LATTER SCENARIO. THE JTWC TRACK FORECAST IS PLACED CLOSE TO THE AI 
MODEL CONSENSUS AND ECMWF DETERMINISTIC GROUPING WITH MEDIUM 
CONFIDENCE THROUGH TAU 72 AND LOW CONFIDENCE THEREAFTER IN RECOGNITION 
OF THE ALTERNATIVE QUASI-STATIONARY SCENARIO. THE INTENSITY GUIDANCE 
VARIES WIDELY DEPENDING ON WHICH TRACK SCENARIO THE MODELS FOLLOW. THE 
JTWC INTENSITY FORECAST ALIGNS WITH THE GUIDANCE THAT REMAINS 
CONSISTENT WITH THE TRACK FORECAST. IT IS WORTH NOTING THAT THE 
INTENSITY GUIDANCE WHICH COINCIDES WITH THE QUASI-STATIONARY SCENARIO 
DEPICTS A MUCH STEEPER RATE OF INTENSIFICATION TO A HIGHER PEAK 
INTENSITY AROUND 100 KTS, THOUGH THAT GUIDANCE IS DISCOUNTED IN THE 
CURRENT FORECAST

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