Advisories

WDPN32 PGTW 011500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 17W (SAUDEL) WARNING NR 
041//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 20.8N 115.7E
   INITIAL INTENSITY: 35 KTS
   GEOGRAPHIC REFERENCE: 123 NM SOUTHEAST OF HONG KONG
   MOVEMENT PAST 6 HOURS: NORTHEASTWARD AT 15 KTS
   SIGNIFICANT WAVE HEIGHT: 18 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS TROPICAL
STORM 17W (SAUDEL) WITH A MOSTLY EXPOSED LOW-LEVEL CIRCULATION
CENTER (LLCC) AND FLARING CONVECTION DISPLACED TO THE SOUTHWEST.
THE SYSTEM CONTINUES TO HAVE A HIGHLY ASYMMETRIC WIND FIELD DUE TO
ITS PLACEMENT ALONG THE NORTHERN SIDE OF STRONG MONSOONAL
SOUTHWESTERLIES. THE STRONGEST WINDS ARE CONFINED TO THE
SOUTHEASTERN QUADRANT, WHICH ARE ENHANCED BY THE MONSOONAL FLOW.
THE INITIAL POSITION IS PLACED WITH HIGH CONFIDENCE BASED ON
LOW-LEVEL CLOUD TRACING IN THE ANIMATED EIR IMAGERY. THE INITIAL
INTENSITY OF 35 KTS IS ASSESSED WITH MEDIUM CONFIDENCE BASED ON THE
AGENCY DVORAK FIXES AND CIMSS INTENSITY ESTIMATES LISTED BELOW.
ENVIRONMENTAL ANALYSIS INDICATES THAT 17W IS LOCATED WITHIN A
MARGINALLY FAVORABLE ENVIRONMENT CHARACTERIZED BY WEAK  OUTFLOW
ALOFT, LOW TO MODERATE (15-20 KTS) VERTICAL WIND SHEAR, AND WARM
(29-30 C) SEA SURFACE TEMPERATURES.

INITIAL WIND RADII BASIS: PERSISTENCE 

CURRENT STEERING MECHANISM: THE NORTHERN PERIPHERY OF A NEAR
EQUATORIAL RIDGE (NER) CENTERED OVER MINDANAO

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T2.0 - 30 KTS
   RJTD: T1.5 - 25 KTS
   RCTP: T2.5 - 35 KTS
   KNES: T2.5 - 35 KTS
   CIMSS SATCON: 38 KTS AT 011240Z
   CIMSS ADT: 39 KTS AT 011220Z
   CIMSS AIDT: 32 KTS AT 011220Z
   CIMSS D-MINT: 32 KTS AT 011130Z
   CIMSS D-PRINT: 32 KTS AT 011220Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY FAVORABLE
   VWS: 15-20 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: WEAK POLEWARD AND EQUATORWARD

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

3. FORECAST REASONING.

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

FORECAST DISCUSSION: TS 17W IS FORECAST TO TRACK NORTHEASTWARD,
ALONG THE NORTHERN PERIPHERY OF THE NER TO THE SOUTH THROUGH TAU
36. AROUND TAU 36, THE SYSTEM WILL ENTER A WEAK STEERING
ENVIRONMENT AS THE NER MOVES OFF TO THE WEST, CAUSING TRACK SPEEDS
TO SLOW. NEAR TAU 48, A BUILDING RIDGE OVER EASTERN CHINA IS
EXPECTED TO GAIN CONTROL AS THE PRIMARY STEERING MECHANISM, TURNING
17W RATHER SHARPLY WESTWARD. 17W WILL THEN CONTINUE ON A WESTWARD
TRACK THROUGH TAU 72, SKIRTING THE COAST OF CHINA, NEAR HONG KONG.
IN TERMS OF INTENSITY, 17W IS FORECAST TO MAINTAIN ITS CURRENT
INTENSITY THROUGH TAU 36 AS THE ENVIRONMENT REMAINS MARGINALLY
FAVORABLE. MODELS SHOW THE SYSTEM STRUGGLING TO CONSOLIDATE DUE TO
THE ASYMMETRY IN THE WIND FIELD AND WEAK OUTFLOW. AFTER TAU 36,
INCREASING EASTERLY SHEAR AND TERRAIN INTERACTION WILL STEADILY
WEAKEN THE VORTEX. DISSIPATION IS FORECAST TO OCCUR AROUND TAU 72,
NORTH OF HONG KONG. HOWEVER, IF THE SYSTEM TURNS MORE SHARPLY
SOUTHWESTWARD AND STAYS OVER WATER RATHER THAN TRACKING INLAND,
THERE IS A POTENTIAL FOR INTENSIFICATION.

MODEL DISCUSSION: MODEL TRACK GUIDANCE IS IN GOOD AGREEMENT ONLY
THROUGH TAU 36, WITH ALL MODELS AGREEING ON A NORTHEASTWARD TRACK.
AFTER TAU 36, GUIDANCE BEGINS TO SPREAD SIGNIFICANTLY. SOME MODELS
SHOW A MORE QUASISTATIONARY MOVEMENT EAST OF HONG KONG WITH A
SHARPER TURN TO THE SOUTHWEST, KEEPING THE SYSTEM OVER WATER FOR
LONGER. THE ECMWF SHOWS THE SHARPEST TURN WHILE THE EC-AIFS TAKES
THE WIDEST TURN. THE JTWC TRACK FORECAST IS PLACED NEAR THE
MULTI-MODEL CONSENSUS THROUGH TAU 48 AND THEN CLOSER TO THE EC-AIFS
AND EXPERIMENTAL GOOGLE DEEPMIND ENSEMBLE MEAN THROUGH TAU 72 WITH
LOW CONFIDENCE. INTENSITY GUIDANCE GENERALLY SHOWS A STEADY
INTENSITY THROUGH TAU 36 FOLLOWED BY STEADY WEAKENING. THE HAFS-A
IS THE QUICKEST TO WEAKEN THE SYSTEM, SHOWING THE SYSTEM
DISSIPATING AS EARLY AS TAU 48 DUE TO AN EARLIER LANDFALL. THE JTWC
INTENSITY FORECAST IS PLACED ABOUT 5 KTS HIGHER THAN THE CONSENSUS.
THE CONFIDENCE IN THE INTENSITY FORECAST IS PLACED WITH LOW
CONFIDENCE DUE TO SMALL CHANGES IN THE TRACK POTENTIALLY CAUSING
SIGNIFICANT CHANGES IN THE INTENSITY OF THE SYSTEM AS IT TRACKS
CLOSE TO THE COAST.

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