Tropical Storm SANBA Advisory Wed Sep 12

MSGID/GENADMIN/NAVMARFCSTCEN PEARL HARBOR HI/JTWC//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 17W (SANBA) WARNING NR
06//
RMKS/
1. FOR METEOROLOGISTS.
2. 12 HOUR SUMMARY AND ANALYSIS.
   A. TROPICAL STORM (TS) 17W (SANBA), LOCATED APPROXIMATELY 640 NM
EAST OF MANILA, PHILIPPINES, HAS TRACKED NORTHWESTWARD AT 08 KNOTS
OVER THE PAST SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE IMAGERY
(MSI) SHOWS DEEP CONVECTIVE BANDING WRAPPING TIGHTLY INTO ALL
QUADRANTS OF THE LOW LEVEL CIRCULATION CENTER. AN 112328Z SSMIS
IMAGE INDICATES A MICROWAVE EYE HAS FORMED WITH THE DEEPEST
CONVECTIVE BANDING ALONG THE NORTHERN AND SOUTHERN PERIPHERY. THE
INITIAL INTENSITY IS BASED ON DVORAK ESTIMATES OF 55 KNOTS FROM KNES
AND PGTW. POSITION IS BASED ON ANIMATED MSI AND THE AFOREMENTIONED
MICROWAVE IMAGERY WITH HIGH CONFIDENCE. UPPER LEVEL ANALYSIS
INDICATES THE SYSTEM IS LOCATED BENEATH AN UPPER LEVEL RIDGE AXIS IN
A REGION OF LIGHT (05-10 KNOTS) VERTICAL WIND SHEAR. ANIMATED WATER
VAPOR IMAGERY CONTINUES TO SHOW RADIAL OUTFLOW, ENHANCED BY A POINT
SOURCE TO THE SOUTH OF THE SYSTEM AND A TROPICAL UPPER TROPOSPHERIC
TROUGH (TUTT) TO THE NORTHEAST. OUTFLOW INTO THE TUTT HAS INCREASED
DURING THE PAST SIX HOURS, RESULTING IN ENHANCED CONVECTIVE BANDING
ON THE POLEWARD SIDE OF 17W. THE CYCLONE IS TRACKING ALONG THE
WESTERN PERIPHERY OF A NEAR-EQUATORIAL RIDGE TO THE EAST.
3. FORECAST REASONING.
   A. NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE PREVIOUS
PROGNOSTIC REASONING MESSAGE.
   B. DUE TO THE INCREASED POLEWARD OUTFLOW AND SUBSEQUENT INCREASE
IN INITIAL INTENSITY, FORECAST INTENSITIES HAVE INCREASED THROUGH
TAU 72. TS 17W IS EXPECTED TO CONTINUE TRACKING NORTHWESTWARD AND
STEADILY INTENSIFY AS UPPER LEVEL CONDITIONS AND WARM (28-30 DEGREES
CELSIUS) SEA SURFACE TEMPERATURES PERSIST. AS THE STEERING REGIME OF
17W TRANSITIONS FROM THE NEAR EQUATORIAL RIDGE TO THE SUBTROPICAL
RIDGE (STR) TO THE EAST OF JAPAN, THIS SYSTEM IS EXPECTED TO BRIEFLY
TRACK ON A MORE NORTHWARD TRAJECTORY NEAR TAU 36. 17W SHOULD RESUME
A SLIGHTLY MORE NORTHWESTERLY TRACK AFTER TAU 36 AS THE SYSTEM MOVES
AROUND THE WESTERN PERIPHERY OF THE STR.
   C. AFTER TAU 72, SANBA IS EXPECTED TO REACH A PEAK INTENSITY OF
115 KNOTS IN A VERY FAVORABLE ENVIRONMENT. 17W WILL BEGIN TO BE
INFLUENCED BY AN APPROACHING MID-LATITUDE TROUGH AT THE 120 HOUR
POINT AND BEGIN RECURVING SOUTH OF THE KOREAN PENINSULA.  AS THE
SYSTEM SLOWLY RECURVES AND BEGINS TO INTERACT WITH THE WESTERLIES,
INTENSITY IS EXPECTED TO GRADUALLY DECREASE. THE AVAILABLE NUMERICAL
MODEL GUIDANCE IS IN GOOD AGREEMENT BEFORE TAU 72, WITH THE
EXCEPTION OF NOGAPS, THE LEFT OUTLIER. AFTER TAU 72, GUIDANCE BEGINS
TO SPREAD SLIGHTLY, WITH ECMWF CONTINUING TO FAVOR A MORE WESTERLY
TRACK WEST OF OKINAWA AND INTO THE YELLOE SEA. NOGAPS AND GFS FAVOR
A MORE EASTERLY TRACK TOWARD THE EASTERN SIDE OF THE KOREAN
PENINSULA. THIS FORECAST IS CLOSE TO CONSENSUS AND IS JUST TO THE
RIGHT OF THE PREVIOUS FORECAST TRACK. CONFIDENCE IN THIS FORECAST IS
HIGH THROUGH TAU 72 AND LOW AFTERWARDS AS GUIDANCE REMAINS SPREAD UP
TO 250 NM.//
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