WDPN31 PGTW 220900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 17W (SAUDEL) WARNING NR 016//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 18.6N 145.8E
   INITIAL INTENSITY: 95 KTS
   GEOGRAPHIC REFERENCE: 204 NM NORTH OF SAIPAN
   MOVEMENT PAST 6 HOURS: NORTHWESTWARD AT 09 KTS
   SIGNIFICANT WAVE HEIGHT: 34 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS TYPHOON 17W
(SAUDEL) WITH A QUICKLY DEVELOPING 20 NM EYE. THERE IS A WEAKNESS
WITHIN THE NORTHEASTERN PORTION OF THE EYEWALL, LIKELY DUE TO THE
WEDGE OF DRY AIR INTRUDING INTO THE VORTEX ABOUT 6 HOURS AGO. THE
SYSTEM HAS BEEN ANALYZED TO HAVE NOW UNDERGONE RAPID
INTENSIFICATION, STRENGTHENING FROM 60 KTS 24 HOURS AGO TO 95 KTS
NOW. A 220617Z F18 SSMIS 91 GHZ MICROWAVE IMAGE REVEALED A DEFINED
BAND OF DEEP CONVECTION NEARLY ENTIRELY SURROUNDING THE CENTER WITH
AN OUTER BAND WRAPPING AROUND THE WESTERN PERIPHERY. THE 37 GHZ
VERSION OF THE SAME SSMIS PASS SHOWED A SYMMETRICAL MICROWAVE EYE
FEATURE AT THE LOWER LEVELS THAT NOW STACKS VERTICALLY WITH HEIGHT.
THE TIMELY SSMIS PASS LENDS HIGH CONFIDENCE TO THE INITIAL
POSITION. THE INITIAL INTENSITY OF 95 KTS IS ASSESSED WITH MEDIUM
CONFIDENCE BASED PRIMARILY ON THE AGENCY DVORAK ESTIMATES OF
T5.0-5.5. THE CIMSS ADT ESTIMATE IS CURRENTLY TOO LOW DUE TO THE
RAPID DEVELOPMENT OF THE EYE AND CONSTRAINTS ON THE CI OUTPUT.
ENVIRONMENTAL ANALYSIS INDICATES THAT 17W IS NOW IN A HIGHLY
FAVORABLE ENVIRONMENT CHARACTERIZED BY STRONG POLEWARD OUTFLOW
ALOFT, LOW (5-10 KTS) VERTICAL WIND SHEAR, AND VERY WARM (30-31 C)
SEA SURFACE TEMPERATURES.

INITIAL WIND RADII BASIS: 212336Z METOP-C ASCAT SCATTEROMETER DATA
AND OBJECTIVE BEST TRACK

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

AGENCY DVORAK AND AUTOMATED FIXES:
   PGTW: T5.5 - 102 KTS
   RJTD: T4.5 - 77 KTS
   RCTP: T5.0 - 90 KTS
   KNES: T5.5 - 102 KTS
   CIMSS ADT: 59 KTS AT 220600Z
   CIMSS AIDT: 67 KTS AT 220600Z
   CIMSS D-MINT: 93 KTS AT 220616Z
   CIMSS D-PRINT: 83 KTS AT 220600Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: HIGHLY FAVORABLE
   VWS: 5-10 KTS
   SST: 30-31 CELSIUS
   OUTFLOW: STRONG POLEWARD

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 TRACK WEST-NORTHWESTWARD
ALONG THE SOUTHWESTERN PERIPHERY OF THE SOUTHWESTERN PERIPHERY OF
THE SUBTROPICAL RIDGE TO THE NORTHEAST THROUGH TAU 48. NEAR TAU 48,
THE STR IS EXPECTED TO MERGE WITH ANOTHER STR POSITIONED OVER
SOUTHERN JAPAN. THE COMBINED STEERING INFLUENCE OF THE RIDGING
COMPLEX WILL KEEP 17W ON A WEST-NORTHWESTWARD TRAJECTORY THROUGH
TAU 96. LANDFALL OVER OKINAWA IS CURRENTLY FORECAST TO OCCUR JUST
BEFORE TAU 96. AFTERWARD, TRACK SPEEDS ARE EXPECTED TO SLOW THROUGH
TAU 120 AS THE PRIMARY STEERING MECHANISM TRANSITIONS TO A
SUBTROPICAL RIDGE POSITIONED OVER EASTERN CHINA. IN TERMS OF
INTENSITY, 17W IS FORECAST TO CONTINUE INTENSIFYING THROUGH TAU 36
TO A PEAK OF AROUND 130 KTS AS THE ENVIRONMENT REMAINS HIGHLY
CONDUCIVE. AFTER TAU 36, THE POLEWARD OUTFLOW CHANNEL WILL WEAKEN
AND NORTHERLY SHEAR WILL BEGIN TO INCREASE, CAUSING 17W TO START ON
A WEAKENING TREND AS IT APPROACHES OKINAWA. THE LANDFALL INTENSITY
IS FORECAST TO BE ABOUT 90 KTS AS IT PASS OVER THE ISLAND. FURTHER
WEAKENING THROUGH TAU 120 IS EXPECTED DUE TO GREATLY INCREASING
NORTHERLY SHEAR CAUSED BY THE STRONG RIDGE OVER EASTERN CHINA.

MODEL DISCUSSION: MODEL TRACK GUIDANCE IS IN GOOD AGREEMENT THROUGH
TAU 72 BESIDES TWO MINOR OUTLIERS IN NAVGEM AND JGSM, WHICH MAKE UP
THE SOUTHERNMOST MODELS. WHEN DISCOUNTING THE TWO SOUTHERN
OUTLIERS, THE CROSS-TRACK SPREAD AT TAU 72 IS MEASURED TO BE ABOUT
125 NM. AFTER TAU 72, CROSS-TRACK SPREAD INCREASES TO 170 NM WITH
NAVGEM AND JGSM REMAINING THE ONLY MODELS SHOWING A TRACK WELL
SOUTH OF OKINAWA. THE JTWC TRACK FORECAST IS PLACED SLIGHTLY NORTH
OF THE MULTI-MODEL CONSENSUS THROUGHOUT THE FORECAST PERIOD WITH
HIGH CONFIDENCE THROUGH TAU 72 AND MEDIUM CONFIDENCE THEREAFTER.
INTENSITY GUIDANCE IS SPLIT BETWEEN THE RAPID INTENSIFICATION (RI)
AIDS AND THE NON-RI AIDS. THE RI AIDS SHOW A PEAK OF 140-150 KTS AT
TAU 36 WHILE HAFS-A AND THE EXPERIMENTAL GOOGLE DEEPMIND ONLY SHOW
A PEAK OF 105-110 KTS. THE JTWC INTENSITY FORECAST IS PLACED CLOSER
TO THE RI AID DEPICTION DUE TO THE EXPECTED HIGHLY FAVORABLE
ENVIRONMENT. MODELS THEN AGREE ON STEADY WEAKENING FROM TAU 48
ONWARD AND THE JTWC INTENSITY FORECAST FOLLOWS SUIT.

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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