WDPN31 PGTW 202100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 17W (SEVENTEEN) 
WARNING NR 001//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 24.8N 124.0E
   INITIAL INTENSITY: 25 KTS
   GEOGRAPHIC REFERENCE: 229 NM WEST-SOUTHWEST OF KADENA AB
   MOVEMENT PAST 6 HOURS: NORTHWESTWARD AT 16 KTS
   SIGNIFICANT WAVE HEIGHT: 12 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
A LATE ARRIVING 201232Z ASCAT PASS PROCESSED UNDER ULTRA HIGH
RESOLUTION REVEALS A CLEAR WINDFIELD OF OVER 25KT WINDS COVERING A
BROAD SECTION OF THE NORTHEAST SECTOR OF INVEST 90W. THEREFORE, JTWC
WILL GO TO WARNING STATUS.  ANIMATED SATELLITE IMAGERY SHOWS THE
LOW LEVEL CIRCULATION (LLC) SHOOTING OUT AND AWAY FROM THE CONVECTIVE
CLOUD SHIELD LEAVING A TIGHTLY WRAPPED BUT FULLY EXPOSED LOW LEVEL
CIRCULATION (LLC) DEVOID OF ANY DEEP CONVECTION. JTWC ASSESSED A T1.5
USING THE SHEAR TECHNIQUE WHICH IS BACKED UP BY THE TIGHTLY WRAPPED
CUMULUS HUMILIS AND STRATOCUMULUS SHOWING IN THE HIGH RESOLUTION
HIMAWARI IMAGERY. LOW TO MID-LEVEL MOISTURE IS ALSO INCREASING
ALONG THE TRACK, AND VERTICAL WIND SHEAR IS ALSO EASING OVER THE 
SOUTHERN SENKAKU ISLANDS AND NORTH OF TAIWAN SO TD 17W WILL BE MORE 
THAN A ONE HIT WONDER.

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

CURRENT STEERING MECHANISM: THE SOUTHEASTERN MOST EXTENSION OF THE
SUBTROPICAL RIDGE. 

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T1.5 - 25 KTS

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINAL
   VWS: 15 KTS
   SST: 28-30 CELSIUS
   OUTFLOW: WEAK EQUATORWARD

ANALYSIS CONFIDENCE:
   INITIAL POSITION: HIGH
   INITIAL INTENSITY: HIGH
   INITIAL WIND RADII: NOT APPLICABLE

3. FORECAST REASONING.

SIGNIFICANT FORECAST CHANGES: THIS INITIAL PROGNOSTIC REASONING
MESSAGE ESTABLISHES THE FORECAST PHILOSOPHY.

FORECAST DISCUSSION: WE HAVE NOT QUITE SEEN THE BEST OF TD 17W BUT
THERE IS NOT A LOT TO LOOK FORWARD TO AS THE SYSTEM WILL TRACK
QUICKLY INTO A LESS HOSTILE ENVIRONMENT AND SURVIVE UNTIL IT PASSES
THE NORTHERN SIDE OF TAIWAN, WHERE IT WILL DISSIPATE IN THE STRAIT.
GRADIENT LEVEL VORTICITY AND STEADY 850MB HEIGHT VALUES INDICATE
THE SYSTEM WILL MAINTAIN AND SLIGHTLY DEEPEN DURING THE NEXT
24 HOURS BEFORE STRETCHING AND LOSING SUPPORT. THE VORTEX WILL
SPUTTER AND STALL AT THE NORTHERN PASSAGE OF THE TAIWAN STRAIT
BEFORE DRIFTING SOUTHWESTWARD WHILE FILLING. 

MODEL DISCUSSION: TRACK GUIDANCE IS CLEAR FOR THE FIRST 24 HOURS
THEN WILDLY DISPARATE AFTERWARDS, SHOWING A POLEWARD-EQUATORWARD
SPLIT. GIVEN THE SHALLOW AND WEAK NATURE OF THE SYSTEM, IT IS MOST
LIKELY THAT THE VORTEX WILL GET KICKED TO THE SOUTH BY A STREAM OF
NEAR GALE FORCE NORTHEASTERLIES THAT SURGE ALONG THE EAST COAST OF
THE CONTINENT NEAR TAU 36. THE INTENSITY FORECAST IS BASED ON A
KICK TO THE SOUTH WHICH IS SUPPORTED BY BOTH HAFS-A AND COAMPS TC.
EVEN IF THE SYSTEM TURNS POLEWARD AS THE EUROPEAN ENSEMBLE
INDICATES, IT WILL BECOME STRETCHED AND MERGE WITH THE
ENVIRONMENT. 

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