WDPN31 PGTW 170300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 23W (TWENTYTHREE) 
WARNING NR 004//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 16.9N 121.8E
   INITIAL INTENSITY: 30 KTS
   GEOGRAPHIC REFERENCE: 146 NM NORTH-NORTHEAST OF MANILA,
PHILIPPINES
   MOVEMENT PAST 6 HOURS: NORTH-NORTHWESTWARD AT 09 KTS
   SIGNIFICANT WAVE HEIGHT: 12 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
AFTER RAPIDLY INTENSIFYING PRIOR TO LANDFALL, ANIMATED MULTISPECTRAL 
SATELLITE IMAGERY DEPICTS 23W NOW INLAND OVER THE MOUNTAINOUS TERRAIN 
OF LUZON, WHICH HAS QUICKLY DISRUPTED THE STORM STRUCTURE. THE VORTEX 
NOW APPEARS TILTED SOUTHWESTWARD WITH HEIGHT, AND THE SURFACE CENTER 
HAS BECOME MORE DIFFICULT TO TRACK. THE INITIAL POSITION IS BASED 
PRIMARILY ON THE LOCUS OF CURVED BANDING IN A 162212Z WSF-M MICROWAVE 
PASS AND RADAR IMAGERY FROM THE PHILIPPINES. THE INITIAL INTENSITY IS 
SET AT 30 KT DUE TO INLAND DECAY AND THE LACK OF WINDS STRONGER THAN 
20 KT IN AVAILABLE SURFACE OBSERVATIONS OVER LUZON. BOTH POLEWARD AND
EQUATORWARD UPPER-LEVEL OUTFLOW CONTINUES TO BE OBSERVED, AND A
WEAK UPPER-LEVEL TROUGH OVER THE LUZON STRAIT IS INDUCING LIGHT
WESTERLY VERTICAL SHEAR OVER THE SYSTEM.

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

CURRENT STEERING MECHANISM: SUBTROPICAL RIDGE TO THE NORTH

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: NO CURRENT ESTIMATE
   RJTD: T1.5 - 25 KTS
   CIMSS D-MINT: 38 KTS AT 162213Z
   CIMSS D-PRINT: 37 KTS AT 162300Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 10-15 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: MODERATE POLEWARD AND EQUATORWARD

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: TROPICAL DEPRESSION 23W IS EXPECTED TO
CONTINUE TRACKING GENERALLY NORTHWESTWARD ACROSS LUZON, EMERGING
OVER THE SOUTH CHINA SEA OR LUZON STRAIT IN ABOUT 12 HOURS. THE
SUBTROPICAL RIDGE SITTING ACROSS EASTERN CHINA AND THE EAST CHINA
SEA WILL CONTINUE TO GUIDE THE STORM NORTHWESTWARD THROUGH 48 HOURS
IN THE DIRECTION OF HONG KONG AND GUANGDONG PROVINCE IN
SOUTHEASTERN CHINA. INTENSIFICATION IS EXPECTED WITHIN A CONDUCIVE, 
LOW-SHEAR ENVIRONMENT AFTER 23W REEMERGES OVER WATER, BUT MAY BE SLOW 
AT FIRST DUE TO THE DESTRUCTION OF THE INNER CORE CAUSED BY
INTERACTION WITH MOUNTAINOUS LUZON. IF A NEW INNER CORE DEVELOPS
QUICKLY, 23W COULD INTENSIFY MORE THAN FORECAST. THE CURRENT JTWC
FORECAST SHOWS A PEAK INTENSITY OF 45 KT, BUT IT SHOULD BE NOTED
THAT THE 48-HOUR AND 72-HOUR FORECAST POINTS STRADDLE THE PROJECTED
LANDFALL TIME, AND THE PEAK INTENSITY BETWEEN THESE POINTS IS
EXPECTED TO BE A BIT HIGHER THAN 45 KT. THE PEAK INTENSITY WILL
ALSO BE SENSITIVE TO THE TOTAL TIME SPENT OVER WATER. NUMERICAL AND
AI-BASED MODELS AGREE THAT THE SUBTROPICAL RIDGE TO THE NORTH WILL
WEAKEN DURING THE 48 TO 72 HOUR PERIOD AS A LONGWAVE TROUGH PASSES
THROUGH NORTHEASTERN CHINA, SLOWING 23W'S FORWARD MOTION. A
RESTRENGTHENING OF THIS RIDGE AROUND 72 HOURS IS THEN EXPECTED TO
TURN THE STORM WESTWARD. UNCERTAINTY IN THE STORM'S FORWARD SPEED
AND THE EXACT LOCATION OF THE WESTWARD TURN INJECTS SOME
UNCERTAINTY INTO THE LANDFALL TIME, AND THUS THE PEAK INTENSITY AS
WELL. A TRACK FARTHER WEST THAT REMAINS OFFSHORE FOR LONGER WILL
LIKELY RESULT IN A HIGHER PEAK INTENSITY, AND A TRACK FARTHER
EAST THAT MAKES LANDFALL EARLIER WILL LIKELY RESULT IN A LOWER
PEAK INTENSITY, ALL ELSE EQUAL.

MODEL DISCUSSION: THE JTWC TRACK FORECAST IS A BIT NORTHEAST OF THE
MULTI-MODEL CONSENSUS, CLOSE TO A BLEND OF THE ECMWF, GFS, HAFS-A,
AIFS, AND OTHER AI-BASED GUIDANCE. THIS TRACK FORECAST IS SLIGHTLY
FASTER AND SLIGHTLY NORTH OF THE PREVIOUS ONE AFTER 36 HOURS. THE
JTWC INTENSITY FORECAST IS CLOSE TO A BLEND OF HAFS-A, COAMPS-TC,
GFS, ECMWF, AND AI-BASED GUIDANCE.

FORECAST CONFIDENCE:
   TRACK 00-72 HR: MEDIUM
   TRACK 72-120 HR: MEDIUM
   INTENSITY 00-72 HR: MEDIUM
   INTENSITY 72-120 HR: MEDIUM//
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