WDPN31 PGTW 212100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 17W (SEVENTEEN) 
WARNING NR 005//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 25.6N 121.0E
   INITIAL INTENSITY: 30 KTS
   GEOGRAPHIC REFERENCE: 40 NM NORTHWEST OF TAIPEI, TAIWAN
   MOVEMENT PAST 6 HOURS: WESTWARD AT 09 KTS
   SIGNIFICANT WAVE HEIGHT: 13 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS TROPICAL
DEPRESSION 17W WITH FLARING CONVECTION OBSCURING THE LOW-LEVEL
CIRCULATION CENTER (LLCC) AND EXPANDING ACROSS THE ENTIRE TAIWAN
STRAIT. ENVIRONMENTAL ANALYSIS INDICATES THAT 17W IS IN A
MARGINALLY FAVORABLE ENVIRONMENT FOR FURTHER DEVELOPMENT
CHARACTERIZED BY WEAK OUTFLOW ALOFT, LOW (5-10 KTS) VERTICAL WIND
SHEAR, AND WARM (29-30 C) SEA SURFACE TEMPERATURES. THE INITIAL
POSITION IS PLACED WITH LOW CONFIDENCE BASED ON THE LLCC BEING
OBSCURED IN THE ANIMATED EIR IMAGERY. THE INITIAL INTENSITY OF 30
KTS IS ASSESSED WITH MEDIUM CONFIDENCE BASED ON THE SUBJECTIVE AND
OBJECTIVE INTENSITY ESTIMATES BELOW.

INITIAL WIND RADII BASIS: NOT APPLICABLE (THERE ARE NO INITIAL WIND
RADII).

CURRENT STEERING MECHANISM: STEERED BY THE NORTHEASTERLY LOW-LEVEL
FLOW.

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T1.5 - 25 KTS
   CIMSS ADT: 35 KTS AT 211800Z
   CIMSS AIDT: 36 KTS AT 211800Z
   CIMSS DPRINT: 29 KTS AT 211800Z

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

ANALYSIS CONFIDENCE:
   INITIAL POSITION: LOW
   INITIAL INTENSITY: MEDIUM
   INITIAL WIND RADII: NOT APPLICABLE

3. FORECAST REASONING.

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

FORECAST DISCUSSION: 17W IS FORECAST TO TRACK WEST-SOUTHWESTWARD
THOUGH THE TAIWAN STRAIT AND TOWARD THE COAST OF CHINA WITH
LANDFALL EXPECTED IN AROUND 12 HOURS. OVER THE NEXT 12 HOURS
ENVIRONMENTAL CONDITIONS ARE EXPECTED TO REMAIN OVERALL CONDUCIVE
AND ALLOW FOR INTENSIFICATION TO AROUND 35 KTS, WHICH COULD
POSSIBLY BE HIGHER DUE TO THE FUNNELING EFFECT THAT TAKES PLACE
WITHIN THE STRAIT. AFTER TAU 12, 17W IS FORECAST TO CONTINUE
TRACKING WEST-SOUTHWESTWARD OVER LAND THROUGH TAU 24. AFTER TAU 24,
THE SYSTEM IS FORECAST TO DRIFT NORTHWESTWARD ALONG THE LOW-LEVEL
FLOW AS IT BEGINS TO ERODE DUE TO TERRAIN INTERACTION. DISSIPATION
OVER LAND IS FORECAST TO OCCUR NEAR TAU 36.  

MODEL DISCUSSION: NUMERICAL MODEL GUIDANCE IS IN POOR AGREEMENT
WITH A WIDE RANGE OF TRACKS BETWEEN MODELS. THERE CONTINUES TO BE
SOME UNCERTAINTY ON IF THE SYSTEM DISSIPATES IN THE TAIWAN STRAIGHT
AS DEPICTED BY ECMWF OR EVEN BEGINS TO TRACK POLEWARD ALONG THE
PERIPHERY OF THE SUBTROPICAL RIDGE TO THE NORTHEAST. HOWEVER, MORE
MODELS ARE SHOWING THE DISSIPATION OVER CHINA SCENARIO AND THE JTWC
TRACK FORECAST REMAINS WITH THAT PHILOSOPHY. THE DIFFERENCES FROM
MODEL TO MODEL LEND LOW CONFIDENCE TO THE JTWC TRACK FORECAST AS A
RESULT. INTENSITY GUIDANCE IS TIED CLOSELY TO THE TYPE OF TRACK 17W
WILL TAKE. GUIDANCE THAT REFLECTS THE JTWC TRACK IS IN RELATIVELY
CLOSE AGREEMENT THOUGH. THE PRIMARY OUTLIER BEING HWRF, WHICH
ACTUALLY TRACKS THE VORTEX MUCH FURTHER SOUTHWESTWARD, SUGGESTS A
HIGHER PEAK OF AROUND 45 KTS. OVERALL, THE JTWC INTENSITY FORECAST
IS PLACED WITH MEDIUM CONFIDENCE PARTIALLY DUE TO THE MINIMAL TIME
BEFORE LANDFALL. 

FORECAST CONFIDENCE:
   TRACK 0 - 72 HR: LOW
   INTENSITY 0 - 72 HR: MEDIUM//
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