WDPN31 PGTW 071500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 24W (YINXING) WARNING NR 018//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 18.6N 121.5E
   INITIAL INTENSITY: 115 KTS
   GEOGRAPHIC REFERENCE: 242 NM NORTH OF MANILA, PHILIPPINES
   MOVEMENT PAST 6 HOURS: WESTWARD AT 09 KTS
   SIGNIFICANT WAVE HEIGHT: 40 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS TYPHOON
(TY) 24W (YINXING) MAKING ITS SECOND LANDFALL IN THE LAST SIX
HOURS, THIS TIME MOVING ASHORE NEAR PATA LIGHTHOUSE ON THE
NORTHWESTERN PORTION OF LUZON, HAVING CROSSED OVER SANTA ANA AROUND
0700Z. THE SYSTEM REMAINED OVER COASTAL WATERS UNTIL JUST AFTER
1200Z WHEN IT MOVED ASHORE ONCE MORE. A 071007Z SSMIS 91GHZ
MICROWAVE IMAGE REVEALED A WELL-DEFINED EYE, WITH A SYMMETRIC
EYEWALL, STRONGEST ON THE NORTHWEST SIDE AND WEAKEST TO THE
SOUTHEAST, BRUSHING THE COAST NEAR APARRI, PHILIPPINES. WITH THE
SYSTEM MAKING LANDFALL NOW, THE EIR SHOWS THAT WHILE THE SYSTEM
MAINTAINED A WELL-DEFINED AND CLEAR EYE AS IT MOVED OVER WATER, THE
EYE STRUCTURE IS RAPIDLY ERODING AS IT MAKES LANDFALL. THE INITIAL
POSITION IS ASSESSED WITH HIGH CONFIDENCE BASED ON THE EYE FEATURE
IN THE ANIMATED EIR AND EXTRAPOLATION OF THE MICROWAVE EYE. THE
INITIAL INTENSITY IS ASSESSED WITH MEDIUM CONFIDENCE, CLOSE TO THE
CIMSS SATCON ESTIMATE AND THE T6.0 FINAL-T NUMBERS FROM MULTIPLE
AGENCIES. OF NOTE, THE RAW CIMSS ADT VALUES HAVE DROPPED
PRECIPITOUSLY, NOW DOWN TO T5.6. THE ENVIRONMENT IN AGGREGATE IS
MARGINALLY FAVORABLE, WITH LOW VWS, WARM SSTS (AWAITING ITS RETURN
OVER WATER) AND STRONG RADIAL OUTFLOW ENHANCED BY A POLEWARD
OUTFLOW CHANNEL. HOWEVER, THE INTERACTION WITH THE RUGGED TERRAIN
OF NORTHWEST LUZON IS OFFSETTING THESE POSITIVE FACTORS AND LEADING
TO RAPID WEAKENING AS IT CROSSES THE ISLAND.

INITIAL WIND RADII BASIS: PERSISTENCE 

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

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T7.0 - 140 KTS 
   RJTD: T6.0 - 115 KTS
   RCTP: T7.0 - 140 KTS 
   KNES: T7.0 - 140 KTS 
   DEMS: T7.0 - 140 KTS 
   CIMSS SATCON: 114 KTS AT 071047Z
   CIMSS ADT: 132 KTS AT 071130Z
   CIMSS D-PRINT: 106 KTS AT 071230Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY FAVORABLE
   VWS: 5-10 KTS
   SST: 27-28 CELSIUS
   OUTFLOW: STRONG POLEWARD
   OTHER FACTORS: LOCALIZED RADIAL OUTFLOW; LAND INTERACTION.

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

3. FORECAST REASONING.

SIGNIFICANT FORECAST CHANGES: THERE ARE NO SIGNIFICANT CHANGES TO
THE FORECAST FROM THE PREVIOUS WARNING.

FORECAST DISCUSSION: TYPHOON 24W WILL CONTINUE TRACKING DUE WEST
OVER THE NEXT 24 HOURS ALONG THE STR FIRMLY ENTRENCHED TO THE
NORTH. THE SYSTEM IS EXPECTED TO EMERGE BACK OVER WATER WITHIN THE
NEXT SIX HOURS, NEAR BANGUI, PHILIPPINES. INTERACTION WITH THE
RUGGED AND HIGH TERRAIN OF NORTHWESTERN LUZON WILL ERODE THE SYSTEM
A SIGNIFICANT AMOUNT, WITH THE INTENSITY EXPECTED TO BE DOWN TO 100
KNOTS BY THE TIME IT MOVES BACK OVER WATER. THOUGH CONDITIONS ARE
EXPECTED TO BE FAVORABLE IN THE NORTHERN PORTION OF THE SOUTH CHINA
SEA (SCS), IT WILL TAKE SOME TIME FOR THE SYSTEM TO RECOVER, AND
INTENSITY IS EXPECTED TO REMAIN RELATIVELY STEADY FOR THE FIRST 36
HOURS OF THE FORECAST. AFTER TAU 36, THE DEEP-LAYER RIDGE TO THE
NORTH WILL BEGIN TO BREAK DOWN DUE TO THE PASSAGE OF THE SOUTHERN
END OF A DEEP MID-LATITUDE TROUGH OVER EASTERN CHINA. THIS
WEAKENING OF THE RIDGE WILL WEAKEN THE STEERING GRADIENT, ALLOWING
TY 24W TO SLOW DOWN AND TURN ONTO A MORE WEST-NORTHWEST TRACK
THROUGH TAU 72. AFTER TAU 48, SOUTHERLY SHEAR WILL DRAMATICALLY
INCREASE, USHERING IN A WEDGE OF DRY AIR INTRUSION, THE COMBINED
EFFECT OF WHICH WILL BE TO DECAPITATE THE VORTEX BETWEEN TAU 48 AND
TAU 72. THE RELATIVELY SHALLOW VORTEX LEFT BEHIND WILL TURN
SOUTHWESTWARD, MOVING ALONG THE EASTERN SIDE OF A LOW- TO MID-LEVEL
STR CENTERED OVER LAOS. NOW FULLY ENGULFED IN DRY AIR, AND WITH A
VERY SHALLOW REMNANT VORTEX, THE SYSTEM WILL STEADILY WEAKEN AS IT
MOVES SOUTHWARD, POTENTIALLY DISSIPATING BY THE END OF THE FORECAST
PERIOD JUST OFF THE COAST OF SOUTHERN VIETNAM.  

MODEL DISCUSSION: DETERMINISTIC TRACK GUIDANCE IS IN VERY GOOD
AGREEMENT THROUGH TAU 72, WITH MINIMAL CROSS- OR ALONG-TRACK SPREAD
BETWEEN THE CONSENSUS MEMBERS. CROSS-TRACK UNCERTAINTY INCREASES
SHARPLY AFTER TAU 72, ESPECIALLY BETWEEN THE TWO OUTLIERS, WITH
NAVGEM DISSIPATING THE SYSTEM JUST OFFSHORE OF HAINAN, WHILE THE
GALWEM TRACKS THE SYSTEM INTO THE CENTRAL SCS, GENERATING A SPREAD
OF 455NM. HOWEVER, BOTH OF THESE TRACKERS REPRESENT UNLIKELY
FORECAST OUTCOMES AND HAVE BEEN DISCARDED FROM THE CONSENSUS. THE
REMAINDER OF THE TRACK GUIDANCE GRADUALLY SPREADS OUT TO 200NM,
BETWEEN THE ECMWF TO THE WEST AND GFS TO THE EAST. THE JTWC
FORECAST TRACES THE CONSENSUS MEAN TO TAU 72, THEN LIES CLOSE TO
THE GEFS ENSEMBLE MEAN THEREAFTER. INTENSITY GUIDANCE IS IN
AGREEMENT BOTH ON THE INTENSITY TREND AND THE PEAK INTENSITY
EXPECTED IN THE SCS, WITH BOTH THE HWRF AND HAFS-A IN AGREEMENT ON
A PEAK OF 105 KNOTS FOLLOWED BY A SHARP WEAKENING AFTER TAU 48. THE
JTWC FORECAST FOLLOWS THESE TWO MODELS CLOSELY THROUGH THE ENTIRE
FORECAST PERIOD. 

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