Tropical Storm KIROGI Advisory Mon Aug 06

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 13W (THIRTEEN) WARNING
NR 06//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TROPICAL STORM 13W (THIRTEEN), LOCATED APPROXIMATELY 460 NM NORTH-
NORTHWEST OF WAKE ISLAND, HAS TRACKED NORTH-NORTHWESTWARD AT 05
KNOTS OVER THE PAST SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE
IMAGERY (MSI) SHOWS THE DEEPEST CONVECTION REMAINS ALONG THE
NORTHERN HALF OF THE SYSTEM WITH FLARING CENTRAL CONVECTION OVER THE
PARTIALLY EXPOSED LOW LEVEL CIRCULATION CENTER (LLCC). THE TRACK HAS
BEEN STEADILY NORTHWARD UNDER THE INFLUENCE OF A NEAR EQUATORIAL
RIDGE TO THE SOUTHEAST OF THE LLCC. THE TRACK SPEED HAS DECREASED AS
THE SYSTEM IS MOVING TOWARD AN AREA OF WEAK STEERING INFLUENCE. MSI
INDICATES THE POLEWARD OUTFLOW CHANNEL CONTINUES TO IMPROVE IN
ASSOCIATION WITH THE HIGH AMPLITUDE TROUGH CURRENTLY LOCATED TO THE
NORTH OF THE SYSTEM. UPPER LEVEL ANALYSIS INDICATES THERE REMAINS A
WEAKENING OUTFLOW CHANNEL TO THE SOUTHEAST INTO AN EASTWARD TRACKING
TROPICAL UPPER TROPOSPHERIC TROUGH. ADDITIONALLY, THE LLCC IS
LOCATED WITHIN A REGION OF MODERATE VERTICAL WIND SHEAR (VWS) (10 TO
20 KNOTS).
3. FORECAST REASONING.
   A. THERE IS NO CHANGE TO THE FORECAST PHILOSOPHY FROM THE PREVIOUS
PROGNOSTIC REASONING BULLETIN.
   B. TS 13W IS EXPECTED TO CONTINUE TRACKING NORTHWARD OVER THE
NEXT 24 HOURS, WITH A BUILDING SUBTROPICAL RIDGE TO THE NORTHEAST
SLOWLY SHIFTING THE TRACK TO THE NORTHWEST THROUGH TAU 72. IMPROVING
OUTFLOW OVER THE NEXT 36 HOURS WILL ALLOW FOR MODEST
INTENSIFICATION. CURRENTLY FAVORABLE SEA SURFACE TEMPERATURES (SST)
WILL SUPPORT THIS INCREASE. HOWEVER, AROUND TAU 36, THE LLCC WILL
MOVE INTO A REGION OF UNFAVORABLE SST'S. INCREASING VWS WILL BEGIN
TO HINDER DEVELOPMENT BEYOND TAU 36 WITH A WEAKENING TREND EXPECTED
BEYOND TAU 48.
   C. BEYOND TAU 72, DECREASING SST'S AND PERSISTENTLY HIGH VWS WILL
ERODE THE SYSTEM DOWN TO 30 KNOTS BY THE END OF THE FORECAST PERIOD.
THERE IS HIGH CONFIDENCE IN THE TRACK FORECAST THROUGH THE ENTIRE
PERIOD. MODEL GUIDANCE OVER THE PAST SIX HOURS HAS SHOWN MARKED
IMPROVEMENT, WITH TIGHT GROUPING THROUGH TAU 120. THERE ARE SOME
SPEED DIFFERENCES IN THE LATER TAUS, BUT FOR THE MOST PART, THERE IS
GOOD AGREEMENT WITHIN THE MODEL GUIDANCE. THIS FORECAST IS CLOSER IN
LINE WITH NGPS BASED ON THE FORECASTED TRACK SPEEDS REMAINING SLOWER
IN THE EXTENDED TAUS AROUND THE STR.//
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