WDPN31 PGTW 041500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 24W (YINXING) WARNING NR 006//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 14.3N 130.1E
   INITIAL INTENSITY: 65 KTS
   GEOGRAPHIC REFERENCE: 529 NM EAST OF MANILA, PHILIPPINES
   MOVEMENT PAST 6 HOURS: NORTHWESTWARD AT 18 KTS
   SIGNIFICANT WAVE HEIGHT: 32 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS A VERY
COMPACT SYSTEM, WITH A SYMMETRICAL AND PERSISTENT CENTRAL DENSE
OVERCAST (CDO) OBSCURING THE LOW LEVEL CIRCULATION CENTER (LLCC).
THE SYSTEM FLIRTED WITH OPENING UP AN EYE JUST AFTER 1200Z, BUT
SUBSEQUENT IMAGERY INDICATES THAT THIS FEATURE DID NOT PERSIST
BEYOND ABOUT 1300Z. A 040908Z SSMIS PASS REVEALED A STRONG AND
WELL-DEFINED MICROWAVE EYE FEATURE IN THE 91GHZ BAND, AND A
SOMEWHAT WEAKER BUT STILL EVIDENT MICROWAVE EYE IN THE 37GHZ BAND.
THE LOWER-LEVEL MICROWAVE EYE WAS OFFSET SLIGHTLY TO THE SOUTHEAST
OF THE UPPER-LEVEL EYE FEATURE, SUPPORTING THE CIMSS ANALYSIS OF
MODERATE (15-20 KNOTS) SOUTHEASTERLY SHEAR PRESENT BELOW THE
OUTFLOW LAYER. THE INITIAL POSITION WAS ASSESSED WITH MEDIUM
CONFIDENCE USING AN EXTRAPOLATION OF THE MICROWAVE EYE FEATURE
DISCUSSED ABOVE, AND PLACED NEAR THE NASCENT EYE IN THE EIR. THE
INITIAL INTENSITY IS INCREASED TO 65 KNOTS WITH MEDIUM CONFIDENCE,
LEADING THE SUBJECTIVE AGENCY FIXES, AS A HEDGE TOWARDS THE MORE
AGGRESSIVE OBJECTIVE FIXES NOTED BELOW AND THE DEVELOPMENT OF THE
STRONG MICROWAVE EYE. THE ENVIRONMENT REMAINS FAVORABLE, WITH LOW
DEEP-LAYER SHEAR, WARM SSTS AND GOOD POLEWARD AND WESTWARD OUTFLOW,
OFFSET SLIGHTLY BY THE MODERATE MID-LEVEL SHEAR.

INITIAL WIND RADII BASIS: PERSISTENCE 

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

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T3.5 - 55 KTS
   RJTD: T2.5 - 35 KTS
   RCTP: T4.0 - 65 KTS
   KNES: T3.5 - 55 KTS
   CIMSS SATCON: 70 KTS AT 041200Z
   CIMSS ADT: 74 KTS AT 041130Z
   CIMSS AIDT: 62 KTS AT 041200Z
   CIMSS DPRINT: 62 KTS AT 041200Z
   CIMSS DMINT: 57 KTS AT 040908Z

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

ANALYSIS CONFIDENCE:
   INITIAL POSITION: MEDIUM
   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 (TY) 24W (YINXING) HAS MAINTAINED A
STEADY NORTHWEST TRACK AT ABOUT 18 KNOTS FOR THE PAST 24 HOURS.
THIS TRACK MOTION IS EXPECTED TO CONTINUE FOR THE NEXT 12 HOURS
BEFORE THINGS BEGIN TO CHANGE. THE RIDGE PATTERN BEGINS TO SHIFT
AFTER TAU 12, AS THE STR TO THE NORTHEAST MOVES FURTHER INTO THE
CENTRAL PACIFIC AND THE PASSAGE OF A MID-LATITUDE TROF OVER KOREA
OPENS UP A BREAK IN THE RIDGE TO THE EAST OF TAIWAN AND WEAKENS THE
STEERING GRADIENT. IN RESPONSE TO THE WEAKENED STEERING PRESSURE,
TY 24W WILL BEGIN TO SLOW DOWN AFTER TAU 12, BUT REMAIN TRACKING
TOWARDS THE NORTHWEST. MORE SIGNIFICANT SLOWING BEGINS AFTER TAU 24
AS THE OUTER EDGES OF THE SYSTEM RUN INTO THE STRONG NORTHEASTERLY
FLOW PUSHING INTO THE PHILIPPINE SEA ON THE LEADING EDGE OF A COLD
SURGE. THE SYSTEM SLOWS TO JUST 4-5 KNOTS AND BEGINS A TURN TOWARDS
THE WEST AS THE LOW- TO MID-LEVEL NORTHEASTERLY FLOW BEGINS TO
EXERT ITSELF UNDER OTHERWISE WEAK STEERING FLOW. AFTER TAU 72,
ANOTHER STR DEVELOPS SOUTHWEST OF HONG KONG AND RAPIDLY EXTENDS
NORTHEASTWARD OVER TAIWAN. TY 24W WILL TURN WESTWARD AND ACCELERATE
AFTER TAU 72 AS THE EAST-WEST ORIENTED RIDGE OVER TAIWAN BECOMES
THE DOMINANT STEERING MECHANISM. TY 24W HAS RAPIDLY INTENSIFIED
OVER THE PAST 24 HOURS UNDER FAVORABLE CONDITIONS. THE FORECAST
CALLS FOR CONTINUE NEAR-RAPID INTENSIFICATION FOR THE NEXT 24
HOURS, WITH THE BULK OF THAT OCCURRING IN THE NEXT 12 HOURS. AFTER
TAU 12, THE SYSTEM BEGINS TO MOVE INTO THE COLD WAKE LEFT BEHIND BY
STY 23W, AS THE TRACKS LIES ON TOP OF THE ACTUAL TRACK OF STY 23W
DURING ITS PEAK IN INTENSITY. THE OCEAN HAS YET TO RECOVER AND SSTS
IN THIS REGION ARE 26-27C AND OHC IS VERY LOW. AS TY 24W MOVES
THROUGH THIS REGION, IT WILL BE AT ITS SLOWEST FORWARD SPEED, AND
THE REDUCED SSTS AND OHC WILL INHIBIT INTENSIFICATION AFTER TAU 24.
AS THE SYSTEM RUNS INTO THE COLD SURGE, INGESTION OF DRY,
RELATIVELY COOL AIR INTO THE WESTERN PORTION OF THE CIRCULATION
WILL ENHANCE THE WEAKENING TREND. AFTER TAU 72, THE SYSTEM MOVES
INTO A MORE FAVORABLE OCEAN ENVIRONMENT, BUT LINGERING DRY AIR AND
INCREASED SHEAR WILL OFFSET GOOD OUTFLOW ALOFT, WITH THE SYSTEM
EXPECTED TO STAGNATE IN TERMS OF INTENSITY AS IT MOVES INTO THE
SOUTH CHINA SEA.  

MODEL DISCUSSION: DETERMINISTIC TRACK GUIDANCE REMAINS IN GOOD
CROSS-TRACK AGREEMENT THROUGH TAU 72, WITH CROSS-TRACK SPREAD
REMAINING RELATIVELY STEADY AT 90NM. HOWEVER, ALONG-TRACK SPREAD
HAS INCREASED SHARPLY SINCE THE PREVIOUS MODEL RUN, WITH 200NM
SEPARATING THE JGSM NEAR THE NORTHWEST TIP OF LUZON AND THE ECMWF
ENSEMBLE MEAN FAR NORTHEAST OF CAPE ENGANO AT TAU 72. BY TAU 120,
UNCERTAINTY IN BOTH THE CROSS- AND ALONG-TRACK DIRECTIONS INCREASES
EVEN MORE. GALWEM TURNS THE SYSTEM TO THE SOUTHWEST, WHILE NAVGEM
TURNS POLEWARD, RESULTING A 225NM SPREAD BY TAU 120, WHILE THE JGSM
AND GFS RACE WESTWARD AT A RAPID PACE, BUT THE ECMWF LAGS, LEADING
TO A 300NM ALONG-TRACK SPREAD. THE JTWC FORECAST SITS ON THE
NORTHERN EDGE OF THE GUIDANCE ENVELOPE THROUGH TAU 72, THEN FOLLOWS
THE CONSENSUS MEAN TO TAU 120. INTENSITY GUIDANCE IS IN GOOD
AGREEMENT, WITH A TIGHTLY CONSTRAINED ENVELOPE WITH A PEAK BETWEEN
90-105 KNOTS. THE JTWC FORECAST RIDES THE CONSENSUS MEAN THROUGH
THE FORECAST PERIOD. 

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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