WDPN31 PGTW 101500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 01W (ONE) WARNING 
NR 001//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 15.0N 113.9E
   INITIAL INTENSITY: 25 KTS
   GEOGRAPHIC REFERENCE: 329 NM EAST OF DA NANG, VIETNAM
   MOVEMENT PAST 6 HOURS: SOUTHWESTWARD AT 05 KTS
   SIGNIFICANT WAVE HEIGHT: 21 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS A
PARTIALLY OBSCURED LOW-LEVEL CIRCULATION WITH PERSISTENT DEEP
CONVECTION DISPLACED TO THE SOUTHWEST, RESULTING FROM SHEAR
INTRODUCED BY A TROPICAL UPPER TROPOSPHERIC TROUGH (TUTT) CELL
POSITIONED TO THE WEST. THE INITIAL POSITION IS PLACED WITH HIGH
CONFIDENCE BASED ON THE AFOREMENTIONED ANIMATED EIR AND A PARTIAL
101239Z METOP-B ASCAT PASS REVEALING THE ASYMMETRIC NATURE OF THE
CIRCULATION. THE INITIAL INTENSITY OF 25 KTS IS ASSESSED WITH
LOW CONFIDENCE BASED ON THE AGENCY AND OBJECTIVE FIXES LISTED
BELOW.

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

CURRENT STEERING MECHANISM: A SUBTROPICAL RIDGE TO THE NORTHEAST

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T1.0 - 25 KTS
   RJTD: T1.5 - 25 KTS

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINAL
   VWS: 15-20 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: MODERATE WESTWARD

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

3. FORECAST REASONING.

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

FORECAST DISCUSSION: TROPICAL DEPRESSION (TD) 01W IS FORECAST TO
TRACK NORTHWESTWARD FOR THE FIRST 72 HOURS OF THE FORECAST UNDER
THE STEERING INFLUENCE OF A DEEP-LAYER SUBTROPICAL RIDGE LOCATED TO
THE NORTHEAST. AFTER CROSSING THE RIDGE AXIS AT TAU 72, TD 01W WILL
BE DRIVEN NORTHEASTWARD ON THE NORTHERN PERIPHERY OF THE
SUBTROPICAL RIDGE. THE SYSTEM WILL MAKE LANDFALL IN THE VICINITY OF
THE LEIZHOU PENINSULA BETWEEN TAU 96 AND 120. IN THE EARLY TERM
FORECAST, STRONG 15-20KT SHEAR WILL PERSIST FOR THE FIRST 24-48 
HOURS, BUT THE TUTT CELL INVOKING THE STRONG SHEAR WILL FILL ALLOWING 
FOR FAVORABLE LOW SHEAR. THE UPPER-LEVEL ENVIRONMENT WILL IMPROVE
ALLOWING FOR STRONG DIFFLUENT OUTFLOW FEEDING INTO A NEARING
UPPER-LEVEL TROUGH ALLOWING FOR A POLEWARD OUTFLOW CHANNEL. THE
SYSTEM WILL PEAK WITH AN INTENSITY OF 55KTS AT TAU 48, FOLLOWED BY
A WEAKENING TREND AS THE TD 01W INTERACTS WITH THE TOPOGRAPHY OF
HAINAN ISLAND BETWEEN TAU 48-72 AND THE LEIZHOU PENINSULA BETWEEN
TAU 96 AND 120.

MODEL DISCUSSION: DETERMINISTIC MODEL GUIDANCE VARIES SIGNIFICANTLY
IN TERMS OF TRACK SPEED, WITH A ALONG-TRACK SPREAD OF 960NM BY THE
END OF THE FORECAST PERIOD, WITH GALWEM, ECMWF, IN THE LEAD AND GFS
AND GEFS FAR BEHIND CONSENSUS. THE DISPARITY BETWEEN THE JTWC
MULTI-MODEL CONSENSUS MEMBERS PRIMARILY STARTS BETWEEN TAU 48-96,
WHEN TD 01W CROSSES THE RIDGE AXIS. THE CROSS-TRACK SPREAD IS A
MAXIMUM OF 200NM IN THE EARLY TERM FORECAST, CONTRIBUTING TO BETTER 
CONFIDENCE. THE INTENSITY GUIDANCE HAS A PEAK AROUND TAU
48 WITH PEAK INTENSITIES RANGING BETWEEN 35-65KTS, WITH HWRF, COAMPS-
TC, AND GFS IN THE HIGHER RANGE AND JTWC SHIPS GUIDANCE IN THE LOWER 
RANGE. 

FORECAST CONFIDENCE:
   TRACK 0 - 72 HR: MEDIUM
   TRACK 72-120 HR: LOW
   INTENSITY 0 - 72 HR: MEDIUM
   INTENSITY 72-120 HR: MEDIUM//
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