Advisories

WDPN31 PGTW 230900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 17W (SAUDEL) WARNING NR 020//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 21.9N 140.9E
   INITIAL INTENSITY: 110 KTS
   GEOGRAPHIC REFERENCE: 768 NM EAST-SOUTHEAST OF KADENA AB
   MOVEMENT PAST 6 HOURS: WEST-NORTHWESTWARD AT 14 KTS
   SIGNIFICANT WAVE HEIGHT: 45 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION: 
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS TYPHOON 17W
(SAUDEL) WITH A SLIGHTLY RAGGED EYE AS THE SYSTEM CONTINUES TO UNDERGO 
AN EYEWALL REPLACEMENT CYCLE (ERC) WHICH HAS STALLED FURTHER 
INTENSIFICATION. THE MSI ALSO SHOWS A STRONG BAND OF CONVECTION 
WRAPPING INTO THE CENTER ALONG THE WESTERN PERIPHERY OF THE SYSTEM. 
THE ERC WAS CONFIRMED BY A 230422Z AMSR2 36 GHZ MICROWAVE IMAGE, WHICH 
SHOWED A CLEAR MOAT FEATURE SURROUNDING THE INNER EYEWALL. THE AMSR2 
IMAGE ALSO REVEALED THAT THE OUTER EYEWALL IS BECOMING MORE DOMINANT, 
HINTING THAT THE ERC IS WELL UNDERWAY. THE INITIAL POSITION IS PLACED 
WITH HIGH CONFIDENCE BASED ON THE EYE IN ANIMATED MSI AND 
EXTRAPOLATION FROM THE AMSR2 IMAGE. THE INITIAL INTENSITY OF 110 KTS 
IS ASSESSED WITH MEDIUM CONFIDENCE BASED ON THE AGENCY DVORAK FIXES 
AND CIMSS INTENSITY ESTIMATES LISTED BELOW. ENVIRONMENTAL ANALYSIS 
INDICATES THAT 17W IS IN A FAVORABLE ENVIRONMENT CHARACTERIZED BY 
STRONG RADIAL OUTFLOW ALOFT, LOW (5-10 KTS) VERTICAL WIND SHEAR, AND 
WARM (29-30 C) SEA SURFACE TEMPERATURES.

INITIAL WIND RADII BASIS: OBJECTIVE BEST TRACK 

CURRENT STEERING MECHANISM: SOUTHWESTERN PERIPHERY OF AN ELONGATED
SUBTROPICAL RIDGE (STR) POSITIONED TO THE NORTHEAST

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T6.0 - 115 KTS
   RJTD: T5.5 - 102 KTS
   RCTP: T6.0 - 115 KTS
   KNES: T5.5 - 102 KTS
   CIMSS SATCON: 114 KTS AT 230600Z
   CIMSS ADT: 112 KTS AT 230600Z
   CIMSS AIDT: 105 KTS AT 230600Z
   CIMSS D-MINT: 115 KTS AT 230417Z
   CIMSS D-PRINT: 109 KTS AT 230600Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 5-10 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: STRONG RADIAL
   OTHER FACTORS: ONGOING EYEWALL REPLACEMENT CYCLE

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: TY 17W IS FORECAST TO CONTINUE TRACKING WEST-
NORTHWESTWARD, ALONG THE SOUTHWESTERN PERIPHERY OF THE STR TO THE 
NORTHEAST THROUGH TAU 24. NEAR TAU 24, THE STR IS EXPECTED TO MERGE 
WITH A SEPARATE STR CENTERED OVER SOUTHERN JAPAN, WHICH WILL KEEP 17W 
ON A WEST-NORTHWESTWARD TRAJECTORY THROUGH TAU 60. LANDFALL OVER 
NORTHERN OKINAWA IS FORECAST TO OCCUR RIGHT AROUND TAU 60. AFTER TAU 
60, TRACK SPEEDS ARE EXPECTED TO SLOW AS THE RIDGING TO THE NORTH 
PROPAGATES EASTWARD AND THE STEERING INFLUENCE TRANSITIONS TO A STR 
CENTERED OVER EASTERN CHINA. 17W IS THEN FORECAST TO BEGIN TRACKING 
WEST-SOUTHWESTWARD, ALONG THE SOUTHEASTERN EXTENT OF THAT STR THROUGH 
THE REMAINDER OF THE FORECAST PERIOD. IN TERMS OF INTENSITY, 17W IS 
NOW FORECAST TO MAINTAIN ITS CURRENT INTENSITY OF 110 KTS THROUGH TAU 
36 AS THE SYSTEM ATTEMPTS TO RECOVER FROM THE ONGOING ERC. 17W IS NOW 
ALSO ENTERING WATERS CONTAINING A LOWER OCEAN HEAT CONTENT (OHC), 
WHICH WILL ALSO SLIGHTLY HINDER THE CHANCES FOR REDEVELOPMENT AFTER 
THE ERC COMPLETES. AFTER TAU 36, NORTHWESTERLY SHEAR AND DRY AIR
ENTRAINMENT FROM THE WEST IS EXPECTED TO INCREASE, CAUSING 17W TO
GRADUALLY WEAKEN AS IT APPROACHES OKINAWA. ONCE THE SYSTEM ENTERS THE 
EAST CHINA SEA, NORTHERLY SHEAR INDUCED BY THE STRONG RIDGE OVER CHINA 
WILL CAUSE FURTHER WEAKENING THROUGH THE REMAINDER OF THE FORECAST 
PERIOD. 

MODEL DISCUSSION: MODEL TRACK GUIDANCE REMAINS IN GOOD AGREEMENT 
THROUGH TAU 72 WITH ONLY NAVGEM BEING AN OUTLIER, WHICH TRACKS THE 
VORTEX MUCH FURTHER SOUTH. DISCOUNTING NAVGEM, THE CROSS-TRACK SPREAD 
AT TAU 72 IS MEASURED TO BE ABOUT 100 NM. AFTER TAU 72, THERE IS QUITE 
A BIT MORE SPREAD BETWEEN MODELS. NOTABLY, THE GFS AND EC-AIFS BOTH 
SHOW A MUCH SHARPER AND FASTER SOUTHWESTWARD TURN THAN THE REMAINDER 
OF GUIDANCE. ON THE OTHER HAND, GALWEM SHOWS NO SOUTHWESTWARD TURN AT 
ALL. THE JTWC TRACK FORECAST IS PLACED CLOSE TO THE MULTI-MODEL 
CONSENSUS THROUGH TAU 72 WITH HIGH CONFIDENCE AND THEN CLOSER TO THE 
ECMWF AND EXPERIMENTAL GOOGLE DEEPMIND ENSEMBLE MEANS THROUGH TAU 120 
WITH MEDIUM CONFIDENCE. INTENSITY GUIDANCE HAS TWO MAIN GROUPINGS. ONE 
IS MADE UP OF COAMPS-TC, GOOGLE DEEPMIND, AND SHIPS, WHICH SHOW A 
STEADY INTENSITY THROUGH TAU 24 FOLLOWED BY STEADY WEAKENING. THE 
OTHER GROUP IS MADE UP OF HAFS-A AND GFS, WHICH SHOW A QUICKER 
WEAKENING TREND IN THE NEAR TERM. THE JTWC INTENSITY FORECAST IS 
PLACED CLOSER TO THE FIRST GROUP WITH OVERALL MEDIUM CONFIDENCE.

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