WDPN31 PGTW 072100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 24W (YINXING) WARNING NR 019//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 18.6N 120.5E
   INITIAL INTENSITY: 100 KTS
   GEOGRAPHIC REFERENCE: 242 NM NORTH OF MANILA, PHILIPPINES
   MOVEMENT PAST 6 HOURS: WESTWARD AT 09 KTS
   SIGNIFICANT WAVE HEIGHT: 36 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS TYPHOON
24W (YINXING) JUST OFF THE NORTHWESTERN COAST OF LUZON WITH A
DEGRADED APPEARANCE IN RESPONSE TO THE TERRAIN INTERACTION. THE EYE
OF 24W HAS NOW FILLED, HOWEVER THE SPIRAL BANDS OF CONVECTION
CONTINUE TO TIGHTLY WRAP INTO THE CENTER. OUTFLOW REMAINS STRONG IN
THE POLEWARD AND EQUATORWARD DIRECTIONS. ENVIRONMENTAL ANALYSIS
INDICATES THAT 24W IS IN A MARGINALLY FAVORABLE ENVIRONMENT
CHARACTERIZED BY LAND INTERACTION OFFSET BY STRONG POLEWARD AND
EQUATORWARD OUTFLOW ALOFT, LOW (5-10 KTS) VERTICAL WIND SHEAR, AND
WARM (27-28 C) SEA SURFACE TEMPERATURES. THE INITIAL POSITION IS
PLACED WITH MEDIUM CONFIDENCE BASED ON THE TIGHTLY WRAPPING
CONVECTION IN THE ANIMATED EIR SATELLITE IMAGERY. THE INITIAL
INTENSITY OF 100 KTS IS ASSESSED WITH MEDIUM CONFIDENCE BASED ON
THE AGENCY DVORAK AND OBJECTIVE INTENSITY ESTIMATES LISTED BELOW.

INITIAL WIND RADII BASIS: ULTRA HIGH RESOLUTION SCATTEROMETER DATA 

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

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T5.5 - 102 KTS
   RJTD: T5.5 - 102 KTS
   KNES: T6.5 - 127 KTS
   CIMSS ADT: 109 KTS AT 071800Z
   CIMSS AIDT: 97 KTS AT 071800Z
   CIMSS DPRINT: 106 KTS AT 071800Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY FAVORABLE
   VWS: 5-10 KTS
   SST: 27-28 CELSIUS
   OUTFLOW: STRONG POLEWARD AND EQUATORWARD
   OTHER FACTORS: TERRAIN INTERACTION WITH NORTHWESTERN LUZON.

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: 24W IS FORECAST TO CONTINUE TRACKING WESTWARD
THROUGH TAU 48 ALONG AN EXTENSION OF THE STR TO THE NORTHEAST. NEAR
TAU 48, A RIDGE CENTERED OVER LAOS AND THAILAND WILL TAKE OVER AS
THE PRIMARY STEERING MECHANISM, CAUSING THE SYSTEM TO TURN
SOUTHWESTWARD. 24W IS EXPECTED TO CONTINUE ON THAT SOUTHWESTWARD
TRACK THROUGH THE REMAINDER OF THE FORECAST PERIOD. REGARDING
INTENSITY, 24W IS FORECAST TO GENERALLY MAINTAIN ITS CURRENT
INTENSITY THROUGH TAU 36 AS IT TRACKS WESTWARD THROUGH THE SOUTH
CHINA SEA DUE TO THE ENVIRONMENT BEING OVERALL FAVORABLE. THE COLD
SURGE FLOWING SOUTHWESTWARD NEAR TAIWAN WILL BE IMPACTING THE
VORTEX BUT IS NOT EXPECTED TO NOTABLY DEGRADE THE CORE OF THE
SYSTEM. STARTING AROUND TAU 48, THE ENVIRONMENT WILL QUICKLY WORSEN
DUE TO INCREASING VERTICAL WINDS SHEAR AND SIGNIFICANT DRY AIR
ENTRAINMENT. AS A RESULT, 24W WILL RAPIDLY WEAKEN AS IT BECOMES
DECOUPLED AND SHEARED APART. DISSIPATION IS EXPECTED TO OCCUR NO
LATER THAN TAU 120, EAST OF CENTRAL VIETNAM. 

MODEL DISCUSSION: NUMERICAL MODEL GUIDANCE IS IN GOOD AGREEMENT
REGARDING THE TRACK OF 24W THROUGH TAU 72. THERE ARE TWO MAIN
OUTLIERS THOUGH, NAVGEM AND JGSM, WHICH TRACK THE VORTEX MUCH
FURTHER WESTWARD AFTER TAU 48 RATHER THAN TAKING THE SOUTHWESTWARD
TURN. AFTER TAU 72, GUIDANCE BEGINS TO DIVERGE DUE TO THE WEAKENING
VORTEX. THE JTWC TRACK IS PLACED CLOSE TO THE CONSENSUS, OFFSET FOR
THE TWO OUTLIERS, WITH HIGH CONFIDENCE THROUGH TAU 72 AND MEDIUM
CONFIDENCE THEREAFTER. INTENSITY GUIDANCE CONTINUES TO BE SPLIT
BETWEEN GLOBAL AND MESOSCALE MODELS. THE GFS SHOWS A MUCH WEAKER
SYSTEM THROUGH TAU 48. THE JTWC INTENSITY FORECAST IS PLACED CLOSE
TO THE HAFS-A AND HWRF WHICH SUGGEST AN INTENSITY OF AROUND 100 KTS
THROUGH TAU 48, WITH RAPID WEAKENING AFTERWARD.  

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