WDPN33 PGTW 291500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 11W (CO-MAY) WARNING NR 
027//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 28.6N 123.4E
   INITIAL INTENSITY: 40 KTS
   GEOGRAPHIC REFERENCE: 185 NM SOUTH-SOUTHEAST OF SHANGHAI, CHINA
   MOVEMENT PAST 6 HOURS: NORTHWESTWARD AT 08 KTS
   SIGNIFICANT WAVE HEIGHT: 16 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED PROXY VISIBLE (PROXYVIS) SATELLITE IMAGERY DEPICTS A
DECOUPLED SYSTEM, WITH DEEP CONVECTION FORMING A MESOSCALE
CONVECTIVE SYSTEM (MCS) NORTH OF THE PARTIALLY EXPOSED LOW LEVEL
CIRCULATION CENTER (LLCC). THE VORTEX IS COMPLEX, WITH MULTIPLE
SPINNERS SEEN SHOOTING OUT FROM UNDER THE MCS OVER THE PAST FEW
HOURS, WITH A LARGE ONE CURRENTLY MOVING EASTWARD INTO THE CLEAR
AIR SOUTHEAST OF THE MCS. THE LLCC IS ASSUMED TO BE A CENTROID
FEATURE, AROUND WHICH THE VISIBLE SPINNERS ARE ROTATING. RADAR DATA
FROM CHINA IS PICKING UP ON A MID-LEVEL ROTATION IN THE CENTER OF
THE MCS, BUT ACTUAL LLCC IS TOO SHALLOW FOR THE RADAR TO DETECT. A
SURFACE OBSERVATION FROM DACHEN DAO SHOWS WINDS FROM THE NNW AT 19
KNOTS, HAVING BACKED OVER THE PAST FEW HOURS FROM NORTHEASTERLY,
SUGGESTIVE OF THE LLCC BEING AT LEAST AT THE SAME LATITUDE OR
SLIGHTLY NORTH. A 290915Z WSF-M 37GHZ MICROWAVE IMAGE REVEALED THE
COMPLEX STRUCTURE OF THE LOW-LEVEL VORTEX, WITH MULTIPLE AREAS OF
ROTATION PRESENT SOUTH OF DEEP CONVECTIVE BANDS. THE INITIAL
POSITION IS ASSESSED WITH LOW CONFIDENCE DUE TO THE PRESENCE OF
MULTIPLE SPINNERS. THE INITIAL INTENSITY IS ASSESSED WITH MEDIUM
CONFIDENCE, HEDGED TOWARDS THE HIGHER END OF THE AVAILABLE
SUBJECTIVE AND OBJECTIVE INTENSITY ESTIMATES. ENVIRONMENTAL
CONDITIONS ARE MARGINALLY UNFAVORABLE, WITH WARM SSTS AND MODERATE
POLEWARD OUTFLOW OFFSET BY MODERATE MID-LEVEL SOUTHERLY SHEAR (AS
INDICATED BY MODEL-DERIVED SOUNDINGS).

INITIAL WIND RADII BASIS: PERSISTENCE 

CURRENT STEERING MECHANISM: SOUTHWESTERN PERIPHERY OF A DEEP-LAYER
SUBTROPICAL RIDGE (STR) OVER JAPAN. 

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T2.0 - 30 KTS
   RJTD: T2.0 - 30 KTS
   RCTP: T2.0 - 30 KTS
   CIMSS ADT: 37 KTS AT 291140Z
   CIMSS AIDT: 40 KTS AT 291140Z
   CIMSS D-PRINT: 37 KTS AT 291140Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY
UNFAVORABLE
   VWS: 10-15 KTS
   SST: 28-29 CELSIUS
   OUTFLOW: MODERATE POLEWARD
   OTHER FACTORS: DRY AIR ACROSS THE SOUTHERN PORTION OF THE
CIRCULATION. DECOUPLED VORTEX. 

ANALYSIS CONFIDENCE:
   INITIAL POSITION: LOW
   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: TROPICAL STORM (TS) 11W IS FORECAST TO
CONTINUE TRACKING NORTHWESTWARD ALONG THE SOUTHWESTERN SIDE OF THE
STR THROUGH THE MAJORITY OF THE FORECAST PERIOD. TS 11W IS FORECAST
TO SKIRT THE OFFSHORE ISLANDS SOUTHEAST OF SHANGHAI AROUND TAU 12,
THEN CROSS HANGZHOU BAY AND MAKE LANDFALL IN THE VICINITY OF
SHANGHAI PRIOR TO TAU 24. ONCE THE SYSTEM MAKES LANDFALL, IT IS
FORECAST TO CONTINUE TRACKING NORTHWESTWARD THROUGH TAU 48. AS THE
SYSTEM DISSIPATES BY TAU 72, THE REMNANT VORTEX WILL TURN
NORTHEASTWARD NEAR GAOYOU LAKE. BOTH THE TIMING AND THE LOCATION OF
LANDFALL MAY DIFFER SIGNIFICANTLY IF THE LOW-LEVEL SPINNER
CURRENTLY PUSHING EASTWARD TURNS OUT TO BE THE ACTUAL CENTER OF THE
TROPICAL STORM. IF THIS IS THE CASE, THE LLCC WILL LIKELY PERFORM A
COUNTER-CLOCKWISE LOOP, THEN RESUME ITS NORTHWESTWARD TRACK, BUT
ARRIVE NEAR SHANGHAI APPROXIMATELY 6-12 HOURS LATER. THE SYSTEM IS
UNLIKELY TO INTENSIFY PRIOR TO LANDFALL DUE TO THE DECOUPLED
STRUCTURE OF THE VORTEX AND LANDFALL INTENSITY IS CURRENTLY
EXPECTED TO BE 40 KNOTS. ONCE THE SYSTEM MOVES ASHORE, IT WILL
RAPIDLY WEAKEN TO THE WEST OF SHANGHAI, MEETING ITS END NEAR GAOYOU
LAKE NO LATER THAN TAU 72. 

MODEL DISCUSSION: DETERMINISTIC TRACK GUIDANCE IS IN GOOD AGREEMENT
THROUGH TAU 48, WITH MINIMAL CROSS- OR ALONG-TRACK SPREAD. AFTER
TAU 48, THE MODELS BEGIN TO SPLIT, WITH ROUGHLY HALF TURNING THE
REMNANT VORTEX NORTHEAST AND HALF TURNING WEST. THE JTWC FORECAST
IS POSITIONED CLOSE TO THE CONSENSUS MEAN THROUGHOUT THE FORECAST
PERIOD. HOWEVER, IN LIGHT OF THE COMPLEX NATURE OF THE LOW-LEVEL
VORTEX AND THE POTENTIAL FOR THE SPINNER CURRENTLY MOVING EASTWARD
TO BE THE ACTUAL LLCC, THERE IS ONLY MEDIUM CONFIDENCE IN THE JTWC
FORECAST TRACK. INTENSITY GUIDANCE IS IN GOOD AGREEMENT ON THE
OVERALL FORECAST, THOUGH BOTH THE CTCX AND HAFS-A SHOW A SMALL
AMOUNT OF INTENSIFICATION PRIOR TO LANDFALL. THE JTWC FORECAST IS
PLACED ON THE CONSENSUS MEAN THROUGH THE FORECAST PERIOD WITH
MEDIUM CONFIDENCE. 

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