Advisories

WDPN31 PGTW 252100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 17W (SAUDEL) WARNING NR 030//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 27.5N 128.1E
   INITIAL INTENSITY: 80 KTS
   GEOGRAPHIC REFERENCE: 62 NM NORTH-NORTHEAST OF KADENA AB
   MOVEMENT PAST 6 HOURS: WEST-NORTHWESTWARD AT 09 KTS
   SIGNIFICANT WAVE HEIGHT: 45 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS TYPHOON
(TY) 17W (SAUDEL) AS A DEGRADING SYSTEM WITH A RECENTLY FORMED
EXPANSIVE DRY SLOT WRAPPING INTO THE CORE FROM THE SOUTHERN
SEMICIRCLE. A RAGGED EYE BRIEFLY REFORMED, BUT QUICKLY COLLAPSED AS
THE HIGH (25-30 KTS) VERTICAL WIND SHEAR (VWS) AND SUBSTANTIAL DRY
AIR ARE CLEARLY TAKING THEIR TOLL ON THE SYSTEM. THE 251625Z AMSR3
MICROWAVE DATA REVEALS A POORLY DEFINED MICROWAVE EYE FEATURE IN
THE LOWER LEVELS AND A BROAD UPPER LEVEL WITH THE BULK OF DEEP
CONVECTION CONFINED TO THE EASTERN QUADRANT. ENVIRONMENTAL ANALYSIS
REVEALS A MARGINAL ENVIRONMENT CHARACTERIZED BY HIGH VWS AND DRY
AIR ENTRAINMENT, OFFSET BY WARM (27-28 C) SEA SURFACE TEMPERATURES
(SST) AND DECENT RADIAL OUTFLOW. THE INITIAL POSITION IS PLACED
WITH HIGH CONFIDENCE BASED ON THE PINHOLE EYE THAT BRIEFLY FORMED
AND WAS VISIBLE IN ANIMATED EIR. THE INITIAL INTENSITY OF 80 KTS IS
ASSESSED WITH MEDIUM CONFIDENCE BASED ON THE CIMSS AUTOMATED
INTENSITY ESTIMATES AND AGENCY DVORAK FIXES LISTED BELOW.

INITIAL WIND RADII BASIS: ADJUSTED WIND RADII USING THE 251305Z
ASCAT UHR DATA

CURRENT STEERING MECHANISM: THE NORTHWESTWARD EXTENSION OF THE
SUBTROPICAL RIDGE CENTERED TO THE NORTHEAST OF THE SYSTEM

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T4.5 - 77 KTS
   RJTD: T4.5 - 77 KTS
   RCTP: T4.0 - 65 KTS
   KNES: T5.0 - 90 KTS
   CIMSS SATCON: 72 KTS AT 251830Z
   CIMSS ADT: 59 KTS AT 251900Z
   CIMSS AIDT: 60 KTS AT 251900Z
   CIMSS D-MINT: 77 KTS AT 251748Z
   CIMSS D-PRINT: 77 KTS AT 251830Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINAL
   VWS: 25-30 KTS
   SST: 27-28 CELSIUS
   OUTFLOW: MODERATE RADIAL
   OTHER FACTORS: DRY AIR ENTRAINMENT

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

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
NORTHWESTWARD FOR THE NEXT 24 HOURS WHILE IT REMAINS UNDER THE
STEERING INFLUENCE OF THE STR CENTERED TO THE NORTHEAST OF THE
SYSTEM. AROUND TAU 12, 17W WILL ENCOUNTER A WEAKNESS IN THE
RIDGE EXTENSION AND SLOW ITS SPEED OF ADVANCE. SIMULTANEOUSLY, A
STR CENTERED OVER EASTERN CHINA WILL BUILD AND ASSUME STEERING
AUTHORITY OF 17W AT AROUND TAU 24 AND INDUCE A SOUTHWESTWARD TRACK
THROUGH TAU 96. WHILE THE STR BUILDS BETWEEN TAU 24-36, SAUDEL'S
TRACK SPEEDS WILL BE RELATIVELY SLOWER, BUT IT IS EXPECTED TO
ACCELERATE AS IT APPROACHES THE COAST AS THE STR STRENGTHENS AND
DRIVES 17W SOUTHWESTWARD. LANDFALL IS FORECAST TO OCCUR BETWEEN TAU
48-60 WITH DISSIPATED EXPECTED OVERLAND NO LATER THAN TAU 96.
REGARDING INTENSITY, 17W IS FORECAST TO GRADUALLY WEAKEN AS THE
ENVIRONMENT REMAINS CONSISTENT FOR THE NEXT 48 HOURS, DEFINED BY
MODERATE TO HIGH (20-30 KTS) VWS AND SIGNIFICANT DRY AIR
ENTRAINMENT, BUT THE STORM IS EXPECTED TO BE PARTIALLY SUSTAINED BY
THE FAVORABLE SSTS AND OUTFLOW. RAPID WEAKENING IS EXPECTED AFTER
LANDFALL WITH DISSIPATION ULTIMATELY OCCURRING BY TAU 96 DUE TO
TERRAIN INTERACTION.

MODEL DISCUSSION: DETERMINISTIC MODEL TRACK GUIDANCE IS IN GOOD
AGREEMENT THROUGH LANDFALL, WITH GSM AND NAVGEM AS THE SOLE
EQUATORWARD OUTLIERS. POST-LANDFALL, THE GUIDANCE ENVELOPE OPENS AS
MODELS DISAGREE ON THE IMPACTS OF LAND INTERACTION. OVERALL, ALL
MODELS DEPICT THE STORM TRACKING SOUTHWESTWARD OVER MAINLAND CHINA
AFTER LANDFALL. THE JTWC TRACK FORECAST IS PLACED NEAR THE
MULTI-MODEL CONSENSUS WITH HIGH CONFIDENCE FROM TAU 0-72, AND
MEDIUM CONFIDENCE FROM TAU 72-96. RELIABLE INTENSITY AIDS ARE IN
STRONG AGREEMENT IN A GRADUAL WEAKENING TREND FOR THROUGH TAU 48,
FOLLOWED BY RAPID DECAY AFTER LANDFALL. AS A RESULT, THE JTWC
INTENSITY FORECAST IS PLACED WITH OVERALL HIGH CONFIDENCE.

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