WDPN31 PGTW 111500
MSGID/GENADMIN/NAVMARFCSTCEN PEARL HARBOR HI/JTWC//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 21W (NEPARTAK)// 
WARNING NR 013//
RMKS/
1. FOR METEOROLOGISTS.
2. 12 HOUR SUMMARY AND ANALYSIS.
    A. TROPICAL STORM (TS) NEPARTAK HAS INTENSIFIED INTO A 55-KNOT
SYSTEM OVER THE LAST 12 HOURS AS ANIMATED INFRARED IMAGERY SHOWS A
MIDGET SYSTEM WITH DEEP, CENTRAL CONVECTION AND GOOD POLEWARD
OUTFLOW INTO THE MID-LATITUDE WESTERLIES. IT APPEARS THAT TS
NEPARTAK HAS CRESTED THE SUBTROPICAL RIDGE AXIS AND IS NOW TRACKING 
STEADILY NORTHEASTWARD. ADDITIONALLY, THOUGH NEPARTAK IS JUST SOUTH
OF THE STRONG UPPER-LEVEL WESTERLIES, IT IS NOT YET SHOWING SIGNS OF
BEING NEGATIVELY IMPACTED BY UNFAVORABLE VERTICAL WIND SHEAR. THE
CURRENT POSITION IS BASED ON POSITION ESTIMATES FROM PGTW AND RJTD
AND THE CURRENT INTENSITY IS SUPPORTED BY A 111037Z 37GHZ TRMM
MICROWAVE IMAGE WHICH REVEALS THE DEVELOPMENT OF A MICROWAVE EYE.
3. FORECAST REASONING.
    A. THE FORECAST PHILOSOPHY HAS CHANGED SINCE THE PREVIOUS
BULLETIN TO REFLECT FASTER TRACK SPEEDS AND INCREASED INITIAL AND
FORECAST INTENSITIES.
    B.  TS 21W IS TRACKING ALONG THE NORTHWESTERN EDGE OF THE
SUBTROPICAL RIDGE AND IS EXPECTED TO CONTINUE TRACKING NORTHEASTWARD
THROUGH THE FORECAST PERIOD. OVER THE NEXT 12 TO 24 HOURS, NEPARTAK
IS EXPECTED TO FURTHER INTENSIFY TO BORDERLINE TYPHOON STRENGTH
AS THE SYSTEM RETAINS FAVORABLE POLEWARD OUTFLOW. BY TAU 36, THE
SUBTROPICAL STEERING RIDGE IS EXPECTED TO STRENGTHEN AND ENABLE
NEPARTAK TO ACCELERATE INTO THE MID-LATITUDES, ALSO SUBJECTING THE
SYSTEM TO UNFAVORABLE VERTICAL WIND SHEAR. ALSO BY TAU 36, THE
TROPICAL CYCLONE IS EXPECTED TO SUCCUMB TO THE INCREASED VERTICAL
WIND SHEAR AND DISSIPATE AS A SIGNIFICANT TROPICAL CYCLONE AFTER TAU
48. THE MODEL GUIDANCE HAS COME INTO VERY GOOD AGREEMENT WITH THIS
TRACK SCENARIO AND THE AIDS NO LONGER SHOW SIGNS OF A SLOWER, MORE
POLEWARD TRACK.//
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