WDPN31 PGTW 281500
MSGID/GENADMIN/NAVMARFCSTCEN PEARL HARBOR HI/JTWC//
SUBJ/PROGNOSTIC REASONING FOR SUPER TYPHOON 26W (NIDA) WARNING NR 
27//
RMKS/
1. FOR METEOROLOGISTS.
2. 12 HOUR SUMMARY AND ANALYSIS.
    A. SUPER TYPHOON (STY) 26W (NIDA), LOCATED APPROXIMATELY 350 NM
SOUTH-SOUTHWEST OF IWO TO, HAS TRACKED NORTH-NORTHEASTWARD AT 02 
KNOTS OVER THE PAST SIX HOURS. ANIMATED INFRARED SATELLITE IMAGERY
SHOWS THAT OVER THE PAST 12 HOURS, STY 26W HAS BEEN SLOWLY OSCIL-
LATING IN A TROCHOIDAL PATTERN IN THE VICINITY OF 19.0N 139.0E. 
STEERING REMAINS ERRATIC AS THE MID-LEVEL SUBTROPICAL RIDGE TO THE
EAST OF STY 26W HAD BEEN WEAKENED RECENTLY BY A TRANSITORY MID-
LATITUDE TROUGH. A ZONAL PATTERN HAS RE-DEVELOPED AS THE TROUGH HAS
MOVED EASTWARD, BUT STY 26W IS STILL WELL SOUTH OF THE STRONG
MID-LATITUDE WESTERLY FLOW (CENTERED NEAR 30N). EXCELLENT RADIAL
OUTFLOW HAS PROVIDED THE EXHAUST MECHANISM ALLOWING NIDA TO MAINTAIN
SUPER TYPHOON INTENSITY FOR THE LAST SEVERAL DAYS. THE CURRENT
INTENSITY IS SLIGHTLY HIGHER THAN THE DVORAK ESTIMATES FROM RJTD AND
PGTW (127 KNOTS), TO REFLECT A SLOWER WEAKENING TREND THAN THE
INTENSITY ESTIMATES INDICATE.
3. FORECAST REASONING.
    A. THE FORECAST PHILOSOPHY HAS NOT CHANGED SIGNIFICANTLY FROM
THE PREVIOUS PROGNOSTIC REASONING BULLETIN.
    B. THE SLOW ERRATIC TRACK OF STY 26W WILL REMAIN IN A GENERALLY
NORTH-NORTHEASTERLY DIRECTION, DUE TO THE WEAK INFLUENCE OF THE MID-
LEVEL STR TO THE EAST. MODEL GUIDANCE INDICATES THAT THE STR WILL
SLOWLY BUILD TO THE WEST AS STY 26W DRIFTS NORTHWARD. BY TAU 24 THE
STR WILL HAVE BUILT IN STRONG ENOUGH TO BECOME THE DOMINANT INFLUENCE
ON THE TRACK OF STY 26W. THE INCREASED LINKAGE WILL HELP TO BRING
ABOUT A SLOW RECURVE TO THE NORTHEAST. AS STY 26W TRACKS TO THE
NORTHEAST, INCREASED INTERACTION WITH THE MID-LATITUDE WESTERLIES
WILL AT FIRST ENHANCE THE POLEWARD OUTFLOW ALLOWING STY 26W TO
PERSIST AS A STRONG TYPHOON THROUGH TAU 48. BETWEEN TAU 48 AND 72
THE VERTICAL WIND SHEAR ASSOCIATED WITH THE WESTERLIES WILL REDUCE
THE POLEWARD OUTFLOW AND WILL BEGIN TO SHEAR THE UPPER AND LOWER
LEVELS APART. ADDITIONALLY, DECREASING OCEAN HEAT CONTENT/SEA SURFACE
TEMPERATURES WILL ENHANCE THE WEAKENING TREND BEYOND TAU 48. MODEL
GUIDANCE REMAINS IN POOR AGREEMENT, WITH JGSM, ECMWF, AND GFS SHOWING
A WESTWARD TRACK, AS WELL AS EGRR AND UKMO SHOWING A NORTHWESTWARD
TRACK. THE REMAINING AIDS SHOW A RECURVE SCENARIO. THE CURRENT
FORECAST REASONING IS FAVORING THE RECURVE MODELS. HOWEVER, NOGAPS
REMAINS THE MOST AGGRESSIVE OF THE AIDS IN TERMS OF TRACK SPEED AND
INTENSITY. THE FORECAST TAKES THESE ELEMENTS INTO CONSIDERATION 
KEEPING THE FORECAST SLIGHTLY SLOWER THAN THE CONSENSUS TO ACCOUNT
FOR DIFFERENCES IN THE WESTWARD TRACKING AIDS, AND NOGAPS FAST
ACCELERATION AND OVERLY HIGH INTENSITY VALUES. 
    C. IN THE EXTENDED TAUS, THERE IS GREATER UNCERTAINTY WITH POOR
AGREEMENT BETWEEN THE AVAILABLE MODEL TRACKERS. THERE IS A 
POSSIBILITY THAT THE SYSTEM MAY WEAKEN AND DISSIPATE PRIOR TO 
COMPLETING ETT AND EITHER SLOW IN FORWARD MOTION OR TRACK UNDER THE 
STRONG LOW-LEVEL NORTHEASTERLY FLOW BACK TO THE SOUTHWEST. THIS 
ALTERNATE SCENARIO IS BASED ON THE LOW-LEVEL STR BUILDING EASTWARD, 
NORTH OF THE SYSTEM, AS IDENTIFIED IN SEVERAL MODELS, AND THE SYSTEM 
TRACKING ALONG THE SOUTHERN EDGE OF THE BAROCLINIC ZONE WHILE 
WEAKENING RAPIDLY.//
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