WDPN31 PGTW 021500
MSGID/GENADMIN/NAVMARFCSTCEN PEARL HARBOR HI/JTWC//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 26W (NIDA) WARNING NR 43//
RMKS/
1. FOR METEOROLOGISTS.
2. 12 HOUR SUMMARY AND ANALYSIS.
    A. TROPICAL STORM (TS) 26W (NIDA), LOCATED APPROXIMATELY 505 NM 
SOUTHEAST OF KADENA, HAS TRACKED WEST-NORTHWESTWARD AT 05 KNOTS OVER 
THE PAST SIX HOURS. AT 0600Z, ANIMATED MULTISPECTRAL SATELLITE 
IMAGERY SHOWED A FULLY EXPOSED LOW LEVEL CIRCULATION CENTER (LLCC) 
NEARLY ONE DEGREE TO THE SOUTHWEST OF INCREASINGLY SHEARED 
CONVECTION. BY 1200Z CONVECTION HAD BEGUN TO BUILD BACK TOWARDS THE 
EXPOSED LLCC AS THE CONVECTIVE MASS ENLARGED UNDER THE INFLUENCE OF 
ENHANCED POLEWARD OUTFLOW INTO THE MID-LATITUDE WESTERLIES. THE 
CONVECTION HAS LEFT THE LLCC MOSTLY OBSCURED AND INCREASINGLY 
DIFFICULT TO LOCATE. THE LATEST MICROWAVE IMAGERY INDICATES A 
WEAKENED LOW LEVEL SIGNATURE AS WELL. THIS WEAKENING SUGGESTS THAT 
THE CURRENT WEST-NORTHWESTWARD TRACK MAY BE MORE A CONSEQUENCE OF 
INCREASED UNCERTAINTY IN THE INITIAL POSITION RATHER THAN THE ACTUAL 
STORM MOTION. THE INITIAL INTENSITY HAS ALSO BEEN ADJUSTED TO 50 
KNOTS, A BLEND OF A 3.5 DVORAK CURRENT INTENSITY (CI) FROM PGTW AND 
A 3.0 FROM RJTD. ANALYSIS OF AMSU TEMPERATURE ANOMALY CROSS SECTIONS 
SHOWS THE WARM CORE HAS CONTRACTED WHILE BECOMING INCREASINGLY 
ASYMMETRIC, AND IT HAS DROPPED SEVERAL THOUSAND FEET INTO THE MID TO 
LOWER TROPOSPHERE. 
3. FORECAST REASONING.
    A. THE FORECAST PHILOSOPHY HAS CHANGED SINCE THE LAST PROGNOSTIC 
REASONING BULLETIN. THE SYSTEM IS NO LONGER EXPECTED TO RECURVE INTO 
THE MID-LATITUDES, BUT RATHER WEAKEN AND DISSIPATE OVER OPEN WATER 
DUE TO VERTICAL WIND SHEAR (VWS). VWS HAS ALREADY INCREASED TO NEAR 
30 KNOTS OVER THE LLCC, HAD LEFT THE LLCC FULLY EXPOSED 6 TO 8 HOURS 
AGO, AND IS EXPECTED TO FURTHER INCREASE OVER THE NEXT 3 DAYS. AS 
THE CONVECTION ONCE AGAIN BECOMES DECOUPLED FROM THE LLCC, THE LLCC 
WILL TEND TO TRACK MORE WEST TO SLIGHTLY SOUTH OF WEST UNDER THE 
INFLUENCE OF (NORTH)EASTERLY SURFACE FLOW. THE CURRENT TRACK SHOWS A 
MORE NORTHWESTWARD THEN WESTWARD TREND AS A CONSEQUENCE OF THE 
PREVIOUS 6-HOUR MOTION. 
    B. THE STORM IS LIKELY TO CONTINUE TO DISSIPATE AS VWS ELEVATES 
OVER THE NEXT 36 HOURS. FOR THE MOST PART THE MODEL GUIDANCE DEPICTS 
A RECURVATURE SCENARIO. AT THIS TIME RECURVATURE STILL SEEMS LESS 
LIKELY BECAUSE THE LLCC HAS ALREADY DECOUPLED FROM ITS CONVECTION 
AND IS BEGINNING TO WEAKEN. HOWEVER, IF CONVECTION REBUILDS AND 
SUSTAINS NEAR THE CENTER (THOUGH UNLIKELY DUE TO VWS), THE MODEL 
GUIDANCE MAY BECOME MORE REPRESENTATIVE OF THE ACTUAL TRACK. AS 
FORECASTED THE STORM WILL BE FULLY DISSIPATED WITHIN 36 HOURS.
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