WDPN31 PGTW 230900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 10W (MA-ON) WARNING NR 004//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 16.2N 123.7E
   INITIAL INTENSITY: 40 KTS
   GEOGRAPHIC REFERENCE: 183 NM EAST-NORTHEAST OF MANILA, PHILIPPINES
   MOVEMENT PAST 6 HOURS: WESTWARD AT 09 KTS
   SIGNIFICANT WAVE HEIGHT: 15 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION: ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS AN EXPOSED LOW LEVEL CIRCULATION CENTER (LLCC) DISPLACED TO THE NORTH OF DEEP FLARING CONVECTION, JUST EAST OF NORTHERN LUZON. THE SHARP NORTHEASTERN EDGE OF CONVECTION IS INDICATIVE OF THE RELATIVELY HIGH NORTHEASTERLY VWS CURRENTLY AFFECTING THE SYSTEM. A WELL-TIMED 220147Z ASCAT-B BULLSEYE PASS SHOWED 35 KNOTS IN ALL QUADRANTS EXCEPT NORTHWEST, AND A BAND OF 40 KNOT WINDS EXTENDING FROM SOUTH TO EAST OF THE LLCC. HENCE, EVEN IN THE FACE OF THE PERSISTENT SHEAR, THE SYSTEM IS MANAGING TO INTENSIFY. THE INITIAL POSITION IS ASSESSED WITH HIGH CONFIDENCE BASED ON THE EXPOSED LLCC, WHILE THE INITIAL INTENSITY IS ASSESSED WITH HIGH CONFIDENCE, HEDGED ABOVE THE AVAILABLE AGENCY AND OBJECTIVE FIXES, BASED ON THE SCATTEROMETER DATA. THE SYSTEM HAS PROGRESSED FURTHER SOUTH THAN ANTICIPATED BUT IS SHOWING SIGNS OF FLATTENING OUT AND MOVING MORE WEST OVER THE PAST SIX HOURS, ALONG THE SOUTHERN SIDE OF A STR TO THE NORTH. THE ENVIRONMENT IS MARGINALLY FAVORABLE WITH STRONG EQUATORWARD OUTFLOW AND VERY WARM SSTS BEING OFFSET BY THE STRONG SHEAR.  

WIND RADII BASIS: SCATTEROMETER DATA 

CURRENT STEERING MECHANISM: SOUTHWESTERN PERIPHERY OF A DEEP-LAYER SUBTROPICAL RIDGE (STR) TO THE NORTH.  

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T2.5 - 35 KTS
   RJTD: T2.0 - 30 KTS
   CIMSS ADT: 32 KTS AT 230540Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY FAVORABLE 
   VWS: 20-25 KTS
   SST: 30-31 CELSIUS 
   OUTFLOW: STRONG EQUATORWARD
   OTHER FACTORS: HIGH OHC

ANALYSIS CONFIDENCE: 
   INITIAL POSITION: HIGH
   INITIAL INTENSITY: HIGH
   INITIAL WIND RADII: HIGH

3. FORECAST REASONING. 

SIGNIFICANT FORECAST CHANGES. THERE IS NO CHANGE TO THE FORECAST PHILOSOPHY SINCE 
THE PREVIOUS PROGNOSTIC REASONING MESSAGE.

FORECAST DISCUSSION: TS MA-ON IS FORECAST TO START TO TURN MORE NORTHWESTWARD IMMINENTLY AS THE STEERING RIDGE IS EXPECTED TO BEGIN TO REORIENT TO A MORE NORTHWEST-SOUTHEAST AXIS. THE SYSTEM IS EXPECTED TO MAKE LANDFALL ALONG THE EAST COAST OF LUZON BY AROUND TAU 12, THEN MOVE ACROSS THE NORTHERN PORTION OF THE ISLAND BEFORE EMERGING BACK INTO THE SOUTH CHINA SEA BETWEEN TAU 24 AND TAU 36. ONCE BACK OVER THE WATER, THE SYSTEM IS FORECAST TO CONTINUE TRACKING NORTHWESTWARD TOWARDS A SECOND LANDFALL JUST SOUTH OF HONG KONG AROUND TAU 72. AS THE SYSTEM HAS ALREADY DEMONSTRATED, IT CAN INTENSIFY EVEN IN THE FACE OF STRONG VWS AND THIS TREND IS EXPECTED TO CONTINUE THROUGH TAU 12, REACHING 50 KNOTS PRIOR TO LANDFALL. TERRAIN INTERACTION WILL CAUSE THE SYSTEM TO WEAKEN SLIGHTLY AS IT MOVES OVER LUZON. ONCE OVER WATER AGAIN BY TAU 36 THE SYSTEM IS FORECAST TO INTENSIFY ONCE AGAIN, BUT AT A SLOW PACE DUE TO A MARGINAL UPPER-LEVEL ENVIRONMENT EXPECTED TO BE IN PLACE AT THAT TIME. WHILE THE FORECAST PEAK IS 55 KNOTS, IT IS POSSIBLE THE SYSTEM COULD REACH A SLIGHTLY HIGHER PEAK BETWEEN TAU 48 AND TAU 72, PRIOR TO LANDFALL. AFTER LANDFALL IN SOUTHERN CHINA, THE SYSTEM WILL RAPIDLY TRACK WESTWARD AND RAPIDLY WEAKEN AND DISSIPATE BY TAU 96. 
 
MODEL DISCUSSION: DETERMINISTIC AND ENSEMBLE TRACK GUIDANCE IS IN GENERALLY GOOD AGREEMENT, WITH A MODERATE AMOUNT OF SPREAD BETWEEN THE NAVGEM ON THE SOUTHERN SIDE OF THE ENVELOPE AND THE ECMWF ON THE NORTHERN SIDE. THE NAVGEM TAKES THE SYSTEM TO JUST NORTH OF HAINAN BY TAU 96, WHILE ECMWF MOVES DIRECTLY OVER HONG KONG. SIMILARLY, THE ENSEMBLE SPREAD IS MODERATE, WITH BOTH THE ECENS AND GEFS ENVELOPE CONSTRAINED BETWEEN NORTHERN HAINAN AND THE VERY SOUTHERN TIP OF TAIWAN. THE JTWC FORECAST TRACK LIES NEAR THE CONSENSUS MEAN, WITH MEDIUM CONFIDENCE. INTENSITY GUIDANCE IS MIXED AND LIMITED DUE TO TECHNICAL ISSUES, BUT WHAT IS AVAILABLE SHOWS A FAIRLY LARGE SPREAD BETWEEN THE COAMPS-TC (GFS) PEAKING AT 75 KNOTS AT TAU 48, AND THE COAMPS-TC (NAVGEM) PEAKING AT ONLY 45 KNOTS. THE JTWC FORECAST LIES BELOW THE CONSENSUS MEAN BY ABOUT 10 KNOTS DUE TO THE EXPECTED MARGINAL UPPER-LEVEL ENVIRONMENT IN THE SOUTH CHINA SEA, WHICH SHOULD INHIBIT MUCH IN THE WAY OF INTENSIFICATION. CONFIDENCE IS LOW DUE TO THE IMPACT OF LAND INTERACTION CROSSING LUZON, AND THE LIMITED GUIDANCE AVAILABLE. 

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