Advisories

WDPN31 PGTW 240300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 17W (SAUDEL) WARNING NR 023//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 23.9N 136.3E
   INITIAL INTENSITY: 110 KTS
   GEOGRAPHIC REFERENCE: 487 NM EAST-SOUTHEAST OF KADENA AB
   MOVEMENT PAST 6 HOURS: WEST-NORTHWESTWARD AT 16 KTS
   SIGNIFICANT WAVE HEIGHT: 46 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS
REDEVELOPMENT AND CLEARING OF AN EYE ONCE AGAIN, WITH DEEP
CONVECTION IN THE FORM OF VORTICAL HOT TOWERS DEVELOPING IN THE
DOWNSHEAR QUADRANTS AND BEGINNING TO WRAP UPSHEAR. A 232243Z SSMIS
91GHZ IMAGE DEPICTS CONCENTRIC EYEWALLS, WHILE THE ANIMATED
MIMIC-TC PRODUCT SUGGESTS THE ERC HAS FINALLY FINISHED, WITH THE
INNER EYEWALL NOW APPROXIMATELY 20 PERCENT LARGER THAN THE EARLIER
EYEWALL. HOWEVER, ANOTHER SECONDARY EYEWALL IS ALREADY IN AN
ADVANCED STAGE OF DEVELOPMENT. THE INITIAL POSITION IS ASSESSED
WITH HIGH CONFIDENCE BASED ON AN EXTRAPOLATION OF THE EARLIER
MICROWAVE IMAGE AND THE EYE FEATURE IN THE MSI. THE INITIAL
INTENSITY IS ASSESSED WITH HIGH CONFIDENCE BASED ON CONGRUENCE OF
THE BULK OF THE OBJECTIVE AND SUBJECTIVE INTENSITY ESTIMATES NOTED
BELOW. ENVIRONMENTAL CONDITIONS CONTINUE TO BE FAVORABLE, WITH LOW
DEEP-LAYER SHEAR, WARM SSTS, RELATIVELY HIGH OHC AND GOOD RADIAL
OUTFLOW ALOFT.

INITIAL WIND RADII BASIS: PERSISTENCE 

CURRENT STEERING MECHANISM: SOUTHWESTERN FLANK OF A DEEP-LAYER
SUBTROPICAL RIDGE (STR) WHICH EXTENDS FROM SOUTHERN JAPAN
SOUTHEASTWARD TO A POINT NORTHEAST OF GUAM. 

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T6.0 - 115 KTS
   RJTD: T6.0 - 115 KTS
   RCTP: T6.0 - 115 KTS
   KNES: T6.0 - 115 KTS
   CIMSS SATCON: 112 KTS AT 240000Z
   CIMSS ADT: 112 KTS AT 240030Z
   CIMSS AIDT: 105 KTS AT 240030Z
   CIMSS D-MINT: 111 KTS AT 232243Z
   CIMSS D-PRINT: 110 KTS AT 240000Z

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

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

3. FORECAST REASONING.

SIGNIFICANT FORECAST CHANGES: THERE ARE NO SIGNIFICANT CHANGES TO
THE FORECAST FROM THE PREVIOUS WARNING.

FORECAST DISCUSSION: TYPHOON (TY) 17W (SAUDEL) WILL CONTINUE
TRACKING NORTHWESTWARD FOR THE NEXT 36 HOURS WHILE GRADUALLY
DECELERATING. THE SYSTEM WILL PASS JUST NORTH OF OKINAWA BETWEEN
TAU 36 AND TAU 48. AFTER TAU 36, THE SYSTEM RAPIDLY DECELERATES AS
IT MOVES SOUTH OF A WEAKNESS IN THE STEERING RIDGE TO THE NORTH
WHILE CONTINUING TO GAIN LATITUDE TOWARDS THE WEAKNESS IN THE
RIDGE. THE SYSTEM REACHES AN INFLECTION POINT, REACHING BOTH ITS
MOST POLEWARD POINT AND SLOWEST FORWARD SPEED, AT TAU 60. BY TAU
72, THE PRIMARY STEERING INFLUENCE SHIFTS TO A BUILDING RIDGE OVER
EASTERN CHINA, ACCELERATING TY 17W TOWARDS THE SOUTHWEST THROUGH THE
REMAINDER OF THE FORECAST PERIOD. LANDFALL ALONG THE SOUTHEAST
COAST OF MAINLAND CHINA IS EXPECTED BETWEEN TAUS 96 AND 120.
REGARDING INTENSITY, BASED ON THE STRUCTURAL EVOLUTION SEEN IN THE
MOST RECENT MICROWAVE IMAGERY AND THE ROBUST VHT ACTIVITY, TY 17W
MAY SEE A SHORT PERIOD OF INTENSIFICATION IN THE NEAR-TERM.
HOWEVER, THE SAME MICROWAVE IMAGERY STRONGLY SUGGESTS THE ONSET OF
ANOTHER ERC IS IMMINENT. THEREFORE, THE INTENSITY FORECAST CALLS FOR
A FLAT INTENSITY TREND FOR THE NEXT 24 HOURS. AS THE SYSTEM
APPROACHES THE RYUKYU ISLANDS, INCREASED SHEAR, COOLER SSTS AND
DECREASED OHC WILL GENERATE A STEADIER RATE OF WEAKENING THROUGH
TAU 96. AFTER MAKING LANDFALL, TY 17W WILL RAPIDLY WEAKEN DUE TO
LAND INTERACTION. 

MODEL DISCUSSION: TRACK GUIDANCE REMAINS IN GOOD AGREEMENT OVERALL.
THROUGH TAU 72, CROSS-TRACK SPREAD HAS ACTUALLY DECREASED SINCE THE
PREVIOUS FORECAST, NOW SITTING AT 100NM BETWEEN THE AI-BASED MODELS
AND GFS ON THE NORTHERN EDGE OF THE ENVELOPE AND THE ECMWF ON THE
SOUTHERN SIDE. ENSEMBLE GUIDANCE IS IN GOOD AGREEMENT THOUGH TAU 72
AS WELL, WITH MINIMAL MEMBER DISPERSION. THE JTWC FORECAST IS
PLACED ON THE NORTHERN SIDE OF THE GUIDANCE ENVELOPE WITH HIGH
CONFIDENCE THROUGH TAU 72. IN THE LONG-RANGE FORECAST, CROSS-TRACK
SPREAD INCREASES TO 245NM BETWEEN THE ECMWF ENSEMBLE MEAN ON THE
NORTHERN EDGE AND THE GFS ON THE SOUTHERN EDGE OF THE ENVELOPE. OF
NOTE, THE GFS DEPICTS A LANDFALL NEAR THE NORTHEAST TIP OF TAIWAN
BEFORE MOVING INTO THE TAIWAN STRAIT, WHILE THE BULK OF THE
GUIDANCE DEPICTS A LANDFALL ON THE EAST COAST OF CHINA. ALONG-TRACK
SPREAD IS DECREASING, BUT THE ECMWF MAINTAINS ITS POSITION AS THE
FASTEST OF THE MODELS, OUTPACING THE REMAINDER OF THE GUIDANCE BY
ROUGHLY 150NM BY TAU 120. THE JTWC FORECAST IS PLACED NEAR THE
EXPERIMENTAL GOOGLE DEEPMIND WITH MEDIUM CONFIDENCE. INTENSITY
GUIDANCE IS IN STRONG AGREEMENT, WITH THE MAJORITY OF MODELS
SHOWING A FLAT INTENSITY TREND THROUGH TAU 24 FOLLOWED BY A STEADY
WEAKENING THROUGH THE REMAINDER OF THE FORECAST PERIOD. 

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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