Tropical Storm JELAWAT Advisory Sun Sep 23

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 18W (JELAWAT) WARNING NR 11//
RMKS//
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TYPHOON (TY) 18W (JELAWAT), LOCATED APPROXIMATELY 485 NM EAST-
SOUTHEAST OF MANILA, PHILIPPINES, HAS TRACKED WESTWARD AT 04 KNOTS
AND INCREASED TO TYPHOON STRENGTH OVER THE PAST SIX HOURS. ANIMATED
MULTISPECTRAL SATELLITE IMAGERY DEPICTS A WELL ORGANIZED LOW-LEVEL
CIRCULATION CENTER (LLCC) WITH A SMALL EYE THAT IS BEGINNING TO
FORM. A 222126Z SSMIS 91 GHZ MICROWAVE IMAGE INDICATES DEEP
CONVECTION ENCIRCLING THE LLCC WITH AN EYEWALL WELL ESTABLISHED AND
A LARGE BAND OF DEEP CONVECTION TO THE SOUTHWEST. UPPER LEVEL
ANALYSIS REVEALS THAT TY 18W HAS CONTINUED EXCELLENT EQUATORWARD
OUTFLOW AND HAS SOME SLIGHT POLEWARD OUTFLOW INTO THE TUTT CELL
JUST NORTHEAST OF THE SYSTEM. LOW (05-10 KNOTS) VERTICAL WIND SHEAR
CONTINUES TO ACT UPON THE SYSTEM. THE INITIAL INTENSITY IS ASSESSED
AT 75 KNOTS BASED ON THE IMPROVED ORGANIZATION AND AN AGREEMENT OF
DVORAK ESTIMATES FROM PGTW AND RJTD. TY 18W HAS SLOWLY DRIFTED WEST
WITHIN A WEAK STEERING ENVIRONMENT DUE TO THE WEAK RIDGE TO THE
NORTHEAST OF THE SYSTEM AND MID-LATITUDE TROUGH CURRENTLY OVER THE
SOUTHERN JAPAN.
3. FORECAST REASONING.
   A. NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE PREVIOUS
REASONING MESSAGE.
   B. TY 18W IS FORECAST TO TRACK SLOWLY NORTHWESTWARD FOR THE NEXT
12 HOURS UNDER THE STEERING INFLUENCE OF THE WEAK RIDGE POSITIONED
NORTHEAST OF THE SYSTEM. THIS STEERING INFLUENCE IS EXPECTED TO BE
SHORT-LIVED AS A MIDLATITUDE SHORTWAVE TROUGH DEEPENS OVER JAPAN.
AFTER TAU 12, THIS TROUGH WILL PROPAGATE FURTHER EASTWARD AND THE
CURRENT STEERING RIDGE IS EXPECTED TO REBUILD AND AMPLIFY, DRIVING
THE SYSTEM ON A MORE POLEWARD TRACK. TY 18W SHOULD CONTINUE TO
INTENSIFY AS IT REMAINS IN FAVORABLE ENVIRONMENTAL CONDITIONS.
DYNAMIC MODELS HAVE BECOME IN BETTER AGREEMENT THROUGH TAU 72,
RULING OUT EGRR AND JGSM WHICH CONTINUALLY TAKE AN UNLIKELY SHARP
TURN TO THE NORTHEAST. THE FORECAST TRACK IS LEFT OF CONSENSUS TO
OFFSET THE UNLIKELY TRACKS OF THESE MODELS. FORECAST CONFIDENCE
REMAINS LOW AS TY 18W HAS YET TO MAKE A MORE NORTHWESTWARD MOTION
AND DUE TO MODELS NOT BEING CONSISTENT.
   C. IN THE EXTENDED TAUS, TY 18W IS FORECAST TO TURN MORE
NORTHWESTWARD AS THE SUBTROPICAL RIDGE CONTINUES TO AMPLIFY.
DYNAMIC MODEL GUIDANCE HAVE YET TO REMAIN CONSISTENT. PREVIOUS
MODEL TRACKS THAT PUT THE LATER TAUS SOUTHWEST OF OKINAWA, JAPAN,
NOW TRACK TOWARDS TAIWAN. DUE TO THIS MODEL INCONSISTENCY, THERE IS
LOW CONFIDENCE IN THE EXTENDED FORECAST. TY 18W WILL REACH A PEAK
INTENSITY OF 115 KNOTS NEAR TAU 96 BUT DUE TO THE TRACK
UNCERTAINTY, THERE IS LOW CONFIDENCE IN THE INTENSITY FORECAST AS
WELL.//
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