Tropical Storm YAMANEKO Advisory lun, 14-11

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 28W (YAMANEKO) WARNING
NR 004//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
SUMMARY:
   INITIAL POSITION: 22.3N 166.0E
   INITIAL INTENSITY: 35 KTS
   GEOGRAPHIC REFERENCE: 183 NM NORTH OF WAKE ISLAND
   MOVEMENT PAST 6 HOURS: NORTHWARD AT 02 KTS
   SIGNIFICANT WAVE HEIGHT: 14 FEET
SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS A FULLY
EXPOSED LOW LEVEL CIRCULATION CENTER (LLCC), AS THE SYSTEM
CONTINUES TO BE SHEARED FROM THE SOUTHWEST, WITH A RAGGED MASS OF
DEEP CONVECTION DISPLACED TO THE NORTHEAST. A 130513Z SSMIS 91GHZ
MICROWAVE IMAGE ALSO INDICATES THE SYSTEM IS IN A SHEARED
ENVIRONMENT AND REVEALS A BROAD LLCC POSITIONED ALONG THE
SOUTHWESTERN EDGE OF A CURVED CONVECTIVE BAND. THE INITIAL POSITION
IS PLACED WITH HIGH CONFIDENCE BASED ON THE MSI LOOP WHICH SHOWS
THE DEFINED LLCC TO THE WEST OF THE CONVECTIVE MASS. THE INITIAL
INTENSITY REMAINS SET AT 35 KNOTS, SLIGHTLY BELOW THE PGTW AND KNES
AGENCY DVORAK INTENSITY ESTIMATES AND CLOSER TO THE ADT OBJECTIVE
INTENSITY ESTIMATE OF 34 KNOTS. ADDITIONALLY, THE MSI INDICATES A
SHEARED TROPICAL CYCLONE, WITH NO APPARENT WRAPPING OF THE
CONVECTION AROUND THE SOUTHWESTERN SIDE OF THE LLCC, THIS STRUCTURE
SUGGEST THAT THE CYCLONE IS NEAR STEADY-STATE. ENVIRONMENTAL
ANALYSIS INDICATES MARGINALLY UNFAVORABLE CONDITIONS, WITH STRONG
POLEWARD OUTFLOW ALOFT, ALONG WITH WARM (27-28C) SEA SURFACE
TEMPERATURES (SSTS), OFFSET BY STRONG (30KT) VERTICAL WIND SHEAR
(VWS).
INITIAL WIND RADII BASIS: PERSISTENCE
CURRENT STEERING MECHANISM: STRONG TRANSITORY RIDGE TO THE NORTH
AND WEAKER SUBTROPICAL RIDGE
(STR) TO THE EAST.
AGENCY DVORAK AND AUTOMATED FIXES:
   PGTW: T3.0 - 45 KTS
   RJTD: T2.0 - 30 KTS
   KNES: T3.0 - 45 KTS
   CIMSS SATCON: 40 KTS AT 130210Z
   CIMSS ADT: 34 KTS AT 130230Z
FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY
UNFAVORABLE
   VWS: 30+ KTS
   SST: 27-28 CELSIUS
   OUTFLOW: STRONG POLEWARD
ANALYSIS CONFIDENCE:
   INITIAL POSITION: HIGH
   INITIAL INTENSITY: MEDIUM
   INITIAL WIND RADII: MEDIUM
3. FORECAST REASONING.
SIGNIFICANT FORECAST CHANGES: THERE ARE NO SIGNIFICANT CHANGES TO
THE FORECAST FROM THE PREVIOUS WARNING.
FORECAST DISCUSSION: TROPICAL STORM 28W (YAMANEKO) CONTINUES TO
MOVE SLOWLY POLEWARD DUE TO A SHALLOW TRANSITORY RIDGE TO THE
NORTH. OVER THE NEXT 12 HOUR THE SYSTEM IS EXPECTED TO CONTINUE ITS
SLOWED TRANSIT NORTHWARD, UNTIL THE TRANSITORY RIDGE MOVES EASTWARD
AND REORIENTS TO A MORE MERIDONAL STATE. AS THIS OCCURS THE SYSTEM
WILL BEGIN TO ACCELERATE NORTHEASTWARD BY THE INFLUENCE OF THE
NORTH-SOUTH ORIENTED RIDGE AS WELL AS AN APPROACHING NEGATIVELY
TILTED UPPER-LEVEL TROUGH TO THE WEST. THE TRACK SPEED IS FORECAST
TO CONTINUE TO ACCELERATE WHILE THE SYSTEM MAINTAINS A
NORTHEASTWARD DIRECTION THROUGH OUT THE FORECAST PERIOD. TS 28W IS
CURRENTLY EMBATTLED BY STRONG VWS, WHICH IS DECOUPLING THE MAIN
CONVECTION FROM THE LLCC AND IS FORECAST TO REMAIN STRONG AND
PERSIST. AS A RESULT, THE SYSTEM IS LIKELY TO MAINTAIN ITS
CURRENT INTENSITY AND REMAIN STEADY THROUGH TAU 36. ADDITIONALLY,
AS THE SYSTEM INTERACTS WITH THE NEGATIVELY TILTED TROUGH. THE
FORECAST CALLS FOR TS 28W TO UNDERGO SUBTROPICAL TRANSITION BY TAU
24 BEFORE QUICKLY PERFORMING EXTRATROPICAL TRANSITION (ETT) WHILE
TRANSFORMING INTO A GALE-FORCE LOW PRESSURE SYSTEM WITH AN
EXPANDING WIND FIELD BY TAU 48.
MODEL DISCUSSION: THE NUMERICAL MODEL GUIDANCE REMAINS IN TIGHT
AGREEMENT WITH A GRADUAL SPREAD TO 200NM BY TAU 48. ADDITIONALLY,
BOTH THE GFS ENSEMBLE (GEFS) MEMBERS AND ECMWF ENSEMBLE (EPS)
MEMBERS ARE IN OVERALL GOOD AGREEMENT THROUGH OUT THE FORECAST
PERIOD. THEREFORE, THE JTWC TRACK FORECAST IS PLACED WITH HIGH
CONFIDENCE AND REMAINS CONSISTENT WITH THE PREVIOUS ONE. THE JTWC
INTENSITY FORECAST IS CONSISTENT WITH THE PREVIOUS INTENSITY
FORECAST AS WELL AND FOLLOWS CLOSE TO THE MULTI-MODEL CONSENSUS, DUE
TO THE HIGH VERTICAL WIND SHEAR, THE INTENSITY FORECAST FOR THE
CURRENT DECOUPLED SYSTEM WILL, REMAIN SLIGHTLY BELOW THE HWRF
SOLUTION, WHICH INDICATES A PEAK NEAR 45 KNOTS.
FORECAST CONFIDENCE:
   TRACK 0 - 72 HR: HIGH
   INTENSITY 0 - 72 HR: MEDIUM//
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