WDPN31 PGTW 170900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 23W (TWENTYTHREE) 
WARNING NR 005//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 17.9N 121.2E
   INITIAL INTENSITY: 30 KTS
   GEOGRAPHIC REFERENCE: 198 NM NORTH OF MANILA, PHILIPPINES
   MOVEMENT PAST 6 HOURS: NORTH-NORTHWESTWARD AT 12 KTS
   SIGNIFICANT WAVE HEIGHT: 12 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS AN OBSCURED
LOW LEVEL CIRCULATION CENTER (LLCC) WITH DEEP CONVECTIVE BANDING
WRAPPING INTO CENTER. ENHANCED WIND WRAPS FROM THE SOUTHERN AROUND
THE EASTERN PERIPHERY ENCOURAGING DEVELOPMENT, WHILE THE WIND FIELD
ALONG THE WESTERN SIDE IS WEAK. AN UPPER-LEVEL CYCLONE TO THE
NORTHWEST IS APPLYING PRESSURE AND VERTICAL WIND SHEAR OF 10-15KTS
LEADING TO A SLIGHT VERTICAL TILT IN THE DISORGANIZED STRUCTURE OF
THE CIRCULATION WHILE OVER LAND. THE INITIAL POSITION IS PLACED
WITH HIGH CONFIDENCE BASED ON THE AFOREMENTIONED ANIMATED MSI AND
AN EARLIER 170441Z GCOM W-1 AMSR2 89GHZ MICROWAVE IMAGE
HIGHLIGHTING THE CIRCULATION STRUCTURE IN THE UPPER-LEVEL
SUPERIMPOSED OVER THE 37GHZ IMAGE. THE INITIAL INTENSITY OF 30 KTS
IS ASSESSED WITH LOW CONFIDENCE BASED ON DISTANT LOCAL
OBSERVATIONS.

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: NO CURRENT ESTIMATE
   RJTD: T1.5 - 25 KTS

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY FAVORABLE
   VWS: 5-10 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: STRONG POLEWARD AND EQUATORWARD

ANALYSIS CONFIDENCE:
   INITIAL POSITION: HIGH
   INITIAL INTENSITY: LOW
   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: TROPICAL DEPRESSION (TD) 23W WILL TRACK
NORTHWESTWARD FOR THE NEST 24 HOUR UNDER THE STEERING INFLUENCE OF
A SUBTROPICAL RIDGE TO THE NORTH. WITHIN THE NEXT 12 HOURS, THE
SYSTEM WILL TRACK OVER WATER AND IMPROVED ENVIRONMENTAL CONDITIONS
FOR CONTINUED DEVELOPMENT. IN THE EARLY-TERM, DEVELOPMENT WILL BE
GRADUAL AS THE VORTEX REDEVELOPS IN THE LOW-LEVEL FLOW. THE
SUBTROPICAL RIDGE TO THE NORTH WILL BREAK DOWN DUE TO APPROACHING
DEEP-LAYER TROUGH TO THE NORTH, ALTERING THE TRACK
WEST-NORTHWESTWARD AFTER TAU 36. CONTINUED UPPER-LEVEL DIVERGENCE,
LOW VERTICAL WIND SHEAR, AND WARM SEA SURFACE TEMPERATURES WILL
ALLOW TD 23W TO PEAK AT TAU 36 AT 45KTS. AS THE SYSTEM APPROACHES
THE COAST, UPWELLING WILL INITIATE WEAKENING AT TAU 48. TD 23W WILL
MAKE LANDFALL BETWEEN TAU 48-72, AND DISSIPATE OVER LAND BY THE END
OF THE FORECAST PERIOD.

MODEL DISCUSSION: DETERMINISTIC MODEL GUIDANCE IS IN GOOD AGREEMENT
THAT TD 23W WILL CURVE NORTHWESTWARD, AND THEN WEST-NORTHWESTWARD
THROUGHOUT THE FORECAST, BUT DOES HAVE MODERATE CROSS-TRACK SPREAD
(215NM) BY THE END OF THE FORECAST. THE MEMBERS OF THE JTWC
MULTI-MODEL CONSENSUS AGREE THAT LANDFALL WILL OCCUR BETWEEN TAU
48-72. MODEL SOLUTIONS THAT REMAIN OVER WATER FOR LONGER PERIODS
INDICATE STRONGER DEVELOPMENT. THE RATE OF DEVELOPMENT IS ALSO
HEAVILY INFLUENCED BY HOW QUICKLY THE LOW-LEVEL STRUCTURE DEVELOPS
WITHIN THE NEXT 12 HOURS AS TD 23W TRACKS BACK OUT OVER WATER. WE
HAVE ALREADY OBSERVED RAPID INTENSIFICATION EARLIER IN THE
FORECAST, AND THE CONDITIONS APPEAR TO CONTINUE TO BE FAVORABLE FOR
RAPID INTENSIFICATION LATER IN THE FORECAST. THE PRIMARY HINDRANCE
IS THE DISORGANIZED LOW-LEVEL FLOW THAT IS SHOWN BY TD 23W.

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