WDPN32 PGTW 300900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR SUPER TYPHOON 09W (SAOLA) WARNING NR 
027//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 20.4N 120.3E
   INITIAL INTENSITY: 135 KTS
   GEOGRAPHIC REFERENCE: 290 NM SOUTH-SOUTHWEST OF TAIPEI, TAIWAN
   MOVEMENT PAST 6 HOURS: WEST-NORTHWESTWARD AT 07 KTS
   SIGNIFICANT WAVE HEIGHT: 48 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
SUPER TYPHOON (STY) 09W (SAOLA) CONTINUES TO DEFY THE ODDS, HAVING
MAINTAINED A STEADY 135 KNOT INTENSITY OVER THE PAST 18 HOURS IN
THE FACE OF PERSISTENT, MODERATE EASTERLY SHEAR. ANIMATED ENHANCED
INFRARED (EIR) IMAGERY INDICATED THAT THE CLOUD TOP TEMPERATURES
WARMED BY ABOUT 10C BETWEEN 0000Z AND 0300Z, BUT THEY HAVE SINCE
RECOVERED WHILE THE EYE TEMPERATURE REMAINS ABOVE 15C. ANIMATED
VISIBLE IMAGERY SHOWS A STADIUM EYE APPROXIMATELY 18NM WIDE,
CONFIRMED BY ANALYSIS OF TAIWAN RADAR DATA. A 300517Z AMSR2 89GHZ
MICROWAVE IMAGE REVEALS A WELL-DEFINED INNER EYEWALL WITH A CLEAR
SECONDARY EYEWALL BEGINNING TO FORM UP AROUND 40-50NM OUT FROM THE
CENTER, AND IS CONFIRMED BY THE SAME FEATURE SEEN IN THE RADAR
DATA. THE INITIAL POSITION IS ASSESSED WITH HIGH CONFIDENCE BASED
ON THE VISIBLE, INFRARED, RADAR AND AMSR2 DATA. THE INITIAL
INTENSITY REMAINS SET AT 135 KNOTS, CONSISTENT WITH THE BULK OF THE
AGENCY DVORAK CURRENT INTENSITY ESTIMATES AS WELL AS THE SUBJECTIVE
ESTIMATES SUCH AS ADT, AIDT, DPRINT AND DMINT, ALL OF WHICH FALL IN
THE RANGE OF 129-135 KNOTS. ADDITIONALLY, AN EARLIER 292156Z RCM-3
SAR PASS SHOWED A MAXIMUM WIND OF 136 KNOTS IN THE SOUTHWESTERN
QUADRANT, PROVIDING ADDITIONAL CONFIDENCE IN INTENSITY TRENDS. THE
SYSTEM CONTINUES TO TRACK WEST-NORTHWEST ALONG THE SOUTHWESTERN
PERIPHERY OF AN EXTENSION OF THE SUBTROPICAL RIDGE (STR) TO THE
NORTHEAST. CONDITIONS REMAIN GENERALLY FAVORABLE WITH WARM SSTS,
AND GOOD RADIAL OUTFLOW WHICH IS ABLE TO PUSH BACK ON THE MODERATE
EASTERLY SHEAR.

INITIAL WIND RADII BASIS: SAR DATA 

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

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T7.0 - 140 KTS 
   RJTD: T7.0 - 140 KTS 
   RCTP: T7.0 - 140 KTS 
   KNES: T7.0 - 140 KTS 
   CIMSS SATCON: 128 KTS AT 300125Z
   CIMSS ADT: 132 KTS AT 300530Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 15-20 KTS
   SST: 30-31 CELSIUS
   OUTFLOW: STRONG RADIAL

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

3. FORECAST REASONING.

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

FORECAST DISCUSSION: STY 09W WILL CONTINUE TRACKING WEST-NORTHWEST
THROUGH TAU 48 UNDER THE INFLUENCE OF THE STR TO THE NORTHEAST. A
COMBINATION OF FACTORS, INCLUDING THE TRACK OF TROPICAL STORM 10W
SOUTH OF OKINAWA AND THE PASSAGE OF A STRONG MID-LATITUDE TROUGH TO
THE NORTH, WILL ERODE THE STEERING RIDGE, LOOSEN THE STEERING
GRADIENT AND LEAD TO A SLOW-DOWN IN THE TRACK SPEED AFTER TAU 24.
IN THE LEE OF THE TROUGH PASSING BY TO THE NORTH, AND TRANSIENT
DEEP-LAYER ANTICYCLONE WILL BUILD IN TO THE WEST OF SHANGHAI, AND
PUSH STY 09W ONTO A MORE WESTWARD TRACK THROUGH TAU 72. THE SYSTEM
IS EXPECTED TO PASS VERY CLOSE TO HONG KONG BUT REMAIN OFFSHORE
THROUGH THE FORECAST PERIOD. AFTER TAU 72, THE TRANSIENT
ANTICYCLONE IS ABSORBED INTO THE LARGER STR TO THE NORTHEAST AND
THE STEERING FLOW QUICKLY WEAKENS, LEAVING STY 09W WITHOUT MUCH
STEERING INFLUENCE, AND THE SYSTEM WILL BECOME QUASI-STATIONARY BY
THE END OF THE FORECAST. IN TERMS OF INTENSITY, WITH CLEAR EVIDENCE
EMERGING OF A SECONDARY EYEWALL, THE ONSET OF AN EYEWALL
REPLACEMENT CYCLE (EWRC) IS IMMINENT IF NOT ALREADY OCCURRING.
THUS, THE SYSTEM IS EXPECTED TO SLOWLY WEAKEN THROUGH THE NEXT 24
HOURS. THE EXACT AMOUNT OF WEAKENING AND HOW LONG IT MAY TAKE FOR
THE EWRC TO COMPLETE ARE UNKNOWN BUT CURRENTLY EXPECTED TO WRAP UP
BY AROUND TAU 24. THE SYSTEM WILL BY THEN BE TAPPING INTO THE
DIFFLUENT EASTERN SIDE OF THE DEEP TROUGH MOVING BY TO THE NORTH,
ALLOWING FOR A SHARP INCREASE IN POLEWARD OUTFLOW. THIS SHOULD
ALLOW THE SYSTEM TO MAINTAIN INTENSITY OR EVEN INTENSIFY SLIGHTLY
UP THROUGH TAU 36. THEREAFTER AS THE SYSTEM APPROACHES THE COAST OF
SOUTHEAST CHINA, SOUTHERLY SHEAR WILL RAPIDLY INCREASE. COMBINED
WITH A REDUCTION IN SSTS, INGESTION OF DRY CONTINENTAL AIR INTO THE
CORE AND DISRUPTION OF THE LOW-LEVEL INFLOW AS IT TRACKS SOUTH OF
HONG KONG, THE SYSTEM WILL RAPIDLY WEAKEN TO JUST 50 KNOTS BY THE
END OF THE FORECAST PERIOD. 

MODEL DISCUSSION: DETERMINISTIC AND ENSEMBLE GUIDANCE HAS COME INTO
MUCH BETTER AGREEMENT OVER THE PAST COUPLE OF MODEL RUNS, WITH
NEARLY ALL OF THE CONSENSUS MEMBERS NOW AGREEING ON AN ARCING TRACK
THAT REMAINS OFFSHORE AND RUNS PARALLEL TO THE CHINESE COAST AFTER
TAU 48. THE LATEST ECMWF AND EGRR TRACKERS ARE THE ONLY OUTLIERS ON
THE NORTHERN SIDE OF THE ENVELOPE WHICH SHOW A LANDFALL IN THE
VICINITY OF HONG KONG AROUND TAU 48, THEN TRACK THE SYSTEM ALONG
THE COASTLINE THROUGH THE REMAINDER OF THE FORECAST. THE JTWC
FORECAST LIES JUST SOUTH OF THE CONSENSUS MEAN, AND JUST NORTH OF
THE GFS DETERMINISTIC AND ENSEMBLE MEAN TRACKERS. CONFIDENCE IS
HIGH OVERALL, BUT VERY SMALL DEVIATIONS OR WOBBLES IN THE CENTER OF
THE SYSTEM, ESPECIALLY AS IT UNDERGOES EYEWALL REPLACEMENT COULD
LEAD TO A SHIFT IN THE FORECAST TRACK OVER LAND. INTENSITY GUIDANCE
IS IN GOOD AGREEMENT OVERALL, THOUGH THE HAFS-A TAKES THE SYSTEM
INLAND WELL EAST OF HONG KONG AND THUS MUST BE DISCOUNTED FROM THE
INTENSITY CONSENSUS. THE CTCX IS CLOSEST THE JTWC FORECAST, SHOWING
A WEAKENING PHASE DUE TO THE EWRC FOLLOWED BY A BRIEF RECOVERY
BEFORE SHARP WEAKENING AFTER TAU 48. THE VAGARIES ASSOCIATED WITH
THE EWRC, SUCH AS THE LENGTH OF THE CYCLE AND THE ULTIMATE LOW
POINT IN THE INTENSITY GENERATE MEDIUM TO LOW CONFIDENCE IN THE
INTENSITY FORECAST. 

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