Advisories

WDPN31 PGTW 242100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 25W (SURIGAE) WARNING NR 
007//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 19.3N 131.7E
   INITIAL INTENSITY: 35 KTS
   GEOGRAPHIC REFERENCE: 483 NM SOUTH-SOUTHEAST OF KADENA AB
   MOVEMENT PAST 6 HOURS: NORTHWESTWARD AT 10 KTS
   SIGNIFICANT WAVE HEIGHT: 16 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS TROPICAL
STORM (TS) 25W (SURIGAE) WITH A SLIGHTLY ELONGATED AND ALMOST ENTIRELY 
EXPOSED LOW LEVEL CIRCULATION CENTER (LLCC) ON THE SOUTHEASTERN 
PERIPHERY OF A PERSISTENT AREA OF CONVECTION. A 241625 AMSR3 89 GHZ 
MICROWAVE IMAGE SUPPORTS THE ELONGATED AND SHEARED NATURE OF 25W, 
SHOWING IT DEVOID OF ANY CONVECTIVE BANDING OUTSIDE OF THE MASS OF 
CONVECTION TO THE NORTHWEST. VERTICAL WIND SHEAR IS EVIDENT IN EIR, 
ALSO SHOWING THAT CONVECTION REMAINS CONFINED TO THE NORTHWEST OF THE 
LLCC DUE TO 10-15 KTS OF VERTICAL WIND SHEAR (VWS), ADDITIONALLY 
INTRODUCING DRY AIR INTO THE SYSTEM AS IT HAS BECOME DECOUPLED FROM 
THE UPPER-LEVEL CONVECTION. THE REMAINDER OF ENVIRONMENTAL CONDITIONS 
REMAIN FAVORABLE WITH WARM (29-30 C) SEA SURFACE TEMPERATURES (SSTS) 
AND MODERATE OUTFLOW ALOFT. THE INITIAL POSITION IS PLACED WITH HIGH 
CONFIDENCE BASED ON THE EXPOSED LLCC AND MICROWAVE IMAGE. THE INITIAL 
INTENSITY IS ASSESSED WITH MEDIUM CONFIDENCE BASED ON THE SLIGHTLY 
LARGER SPREAD BETWEEN AGENCY DVORAK FIXES AND OBJECTIVE ESTIMATES 
LISTED BELOW.

INITIAL WIND RADII BASIS: PERSISTENCE 

CURRENT STEERING MECHANISM: SUBTROPICAL RIDGE CENTERED TO THE
NORTH-NORTHEAST 

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T3.0 - 45 KTS
   RJTD: T2.5 - 35 KTS
   RCTP: T2.5 - 35 KTS
   CIMSS SATCON: 43 KTS AT 241647Z
   CIMSS ADT: 47 KTS AT 241740Z
   CIMSS AIDT: 38 KTS AT 241740Z
   CIMSS D-MINT: 33 KTS AT 241648Z
   CIMSS D-PRINT: 31 KTS AT 241740Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY FAVORABLE
   VWS: 10-15 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: MODERATE POLEWARD
   OTHER FACTORS: VORTEX DECOUPLING AND DRY AIR ENTRAINMENT

ANALYSIS CONFIDENCE:
   INITIAL POSITION: HIGH
   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 TAKEN A SLIGHTLY MORE NORTHWESTWARD
JOG OVER THE LAST SIX HOURS THAN PREVIOUSLY FORECAST, BUT IS FORECAST 
TO CONTINUE A GENERAL WEST-NORTHWESTWARD TRACK AT A STEADY RATE FOR 
THE NEXT 24 HOURS. AFTER TAU 24, 25W IS FORECAST TO SLOW IN TRACK 
SPEED AND TURN POLEWARD AS IT APPROACHES A WEAKNESS IN THE RIDGING 
BETWEEN THE PRIMARY STEERING SUBTROPICAL RIDGE (STR) CENTERED TO THE 
NORTH-NORTHEAST AND ANOTHER STR CENTERED OVER SOUTHERN CHINA. 25W IS 
EXPECTED TO MOVE SLOWLY POLEWARD UNTIL AROUND TAU 72 AT WHICH POINT IT 
IS FORECAST TO TURN NORTHEASTWARD AND RECURVE THE STR TO THE EAST. 
THERE REMAINS UNCERTAINTY IN THE RESULTANT TRACK AND TRACK SPEED IN 
THIS OUTCOME AS GLOBAL MODEL FIELDS DEPICT VARYING STEERING 
ENVIRONMENTS DURING THIS TIME OF RECURVATURE BETWEEN TAUS 48 AND 96, 
BOTH IN REGARDS TO THE DISPOSITION OF THE TWO STRS, AS WELL AS THE 
POSSIBLE IMPACTS OF A MID-LATITUDE SHORTWAVE TROUGH PROPAGATING 
EASTWARD. THE GFS MODEL FIELD DEPICTS THE STR TO THE EAST RECEDING AS 
WELL AS THE MID-LAT TROUGH WITHOUT ENOUGH SUPPORT TO PULL 25W POLEWARD 
AND INSTEAD DEPICTS THE SYSTEM SLOWING IN TRACK SPEED AND STALLING 
JUST SOUTH OF THE RYUKYU ISLANDS FOR THE REMAINDER OF THE FORECAST 
PERIOD. ALTERNATIVELY, THE ECMWF AND AI MODEL FIELDS ASSESS THE TROUGH 
TO HAVE MORE DYNAMIC SUPPORT TO BRING 25W POLEWARD AROUND TAU 72 IN 
CONJUNCTION WITH THE EASTERN STR MAINTAINING STRONGER STEERING 
INFLUENCE FOR THE ENTIRETY OF THE FORECAST PERIOD, AND IS ULTIMATELY 
WHAT IS DEPICTED IN THE OFFICIAL JTWC FORECAST TRACK. REGARDING 
INTENSITY, 25W IS FORECAST TO GRADUALLY INTENSIFY OVER THE NEXT 24 
HOURS AS IT AXISYMMETRIZES, VWS ABATES, AND IT IMPROVES IN VERTICAL 
STRUCTURE. FROM TAU 24 TO 48 A PERIOD OF RAPID INTENSIFICATION (RI) IS 
FORECAST AS 25W NEARS THE AXIS OF RIDGING AND SUBSEQUENT ENHANCED 
OUTFLOW. A PEAK OF AROUND 95 KTS IS EXPECTED TO OCCUR BETWEEN TAUS 60 
AND 72 AFTER THIS RI BEFORE A STEADY WEAKENING PHASE BEGINS DUE TO 
INCREASED VWS AND SUBSEQUENT DRY AIR ENTRAINMENT. THERE IS ALSO 
UNCERTAINTY WITH THE INTENSITY FORECAST DUE TO IT BEING HIGHLY 
DEPENDENT ON THE ULTIMATE TRACK OF 25W. THE ALTERNATE SCENARIO 
DEPICTED BY GFS COULD RESULT IN A HIGHER PEAK INTENSITY IF 25W REMAINS 
IN AN AREA OF MORE FAVORABLE CONDITIONS.

MODEL DISCUSSION: TRACK MODEL GUIDANCE REMAINS DIVIDED INTO THREE MAIN 
GROUPINGS OF A STRAIGHT NORTHWESTWARD TRACK FOR THE REMAINDER OF THE 
FORECAST PERIOD AND TWO RECURVING SCENARIOS WITH THE REMAINDER OF 
PHYSICS-BASED MODELS BEING MARKEDELY SLOWER THAN THE FINAL GROUP WHICH 
IS MADE UP OF THE AI GUIDANCE AND DEPICTS THE QUICKEST RECURVATURE AND 
NORTHEASTWARD TRACK. THIS HAS RESULTED IN A TOTAL ALONG TRACK SPREAD 
OF 700 NM BY TAU 120 BETWEEN THESE THREE GROUPS. AS DISCUSSED ABOVE, 
THE OFFICIAL JTWC FORECAST TRACK IS LAID IN AGREEMENT WITH THE 
STEERING SCENARIO DEPICTED BY ECMWF AND AI GUIDANCE IN A RECURVATURE 
SCENARIO, CLOSELY IN LINE WITH THE MULTI-MODEL AND AI CONSENSUS TRACK 
FOR THE ENTIRETY OF THE FORECAST PERIOD AND IN LINE WITH THE MULTI-
MODEL CONSENSUS TRACK SPEED OUT TO TAU 72, THEN BLENDING THE TRACK 
SPEEDS OF THE MULTI-MODEL AND AI CONSENSUS FROM TAU 72 TO 120 AS THEY 
BEGIN TO DIVERGE, WITH OVERALL LOW CONFIDENCE DUE TO THE LARGE SPREAD 
IN GUIDANCE. MODEL INTENSITY GUIDANCE ALSO REMAINS SPLIT AS THE MOST 
RELIABLE INTENSITY AIDS DEPICT VERY DIFFERENT TRACK OUTCOMES WITH 
COAMPS-TC AND HAFS-A STALLING 25W SOUTH OF THE RYUKYU ISLANDS AND THUS 
DEPICTING 25W REACHING NEAR SUPERTYPHOON INTENSITIES, WHEREAS THE 
GOOGLE DEEPMIND DEPICTS AN EARLIER AND LOWER PEAK OF 80 KTS AS IT 
TRACKS THE SYSTEM MUCH MORE QUICKLY THROUGH THE RECURVATURE. HOWEVER, 
BOTH AI AND MESOSCALE ENSEMBLE INTENSITY GUIDANCE CONTINUE TO SHOW 
SUPPORT FOR RI TO OCCUR BETWEEN TAUS 24 TO 60, LENDING SOME CONFIDENCE 
TO THAT PORTION OF THE FORECAST. ALL GUIDANCE IS IN GOOD AGREEMENT ON 
A SHORT TERM STEADY INTENSIFICATION PRIOR TO THE POSSIBLE RI, AS WELL 
AS AGREEMENT ON A GENERAL WEAKENING TREND AFTER TAU 72, HOWEVER THE 
HIGHEST UNCERTAINTY REMAINS WITH THE TIMING AND MAGNITUDE OF PEAK 
INTENSITY. AS SUCH, THE OFFICIAL JTWC INTENSITY FORECAST IS
ASSESSED WITH LOW CONFIDENCE THROUGHOUT THE FORECAST PERIOD, IN GOOD 
AGREEMENT WITH THE MULTI-MODEL CONSENSUS OUT TO TAU 48 AND THEN ABOVE 
IT TO BETTER CAPTURE THE EXPECTED RI PERIOD, COMING BACK INTO 
AGREEMENT WITH THE CONSENSUS BY TAU 96.

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