WDPN31 PGTW 221500
MSGID/GENADMIN/NAVMARFCSTCEN PEARL HARBOR HI/JTWC//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 02W WARNING NR 04//
RMKS/
1. FOR METEOROLOGISTS.
2. 12 HOUR SUMMARY AND ANALYSIS.
TROPICAL DEPRESSION (TD) 02W, LOCATED APPROXIMATELY 240 NM EAST-
SOUTHEAST OF YAP, HAS TRACKED NORTHWESTWARD AT 09 KNOTS OVER THE 
PAST 06 HOURS. THE TD HAS BEEN UNABLE TO STRENGTHEN TO TROPICAL
STORM STRENGTH OVER THE PAST 12 HOURS DUE TO MARGINAL UPPER LEVEL
CONDITIONS AND WEAK SUPPORTING WESTERLIES ON THE EQUATORWARD SIDE
OF THE DEPRESSION AS CONFIRMED BY A 220052Z ASCAT PASS. MODERATE
EASTERLY FLOW ALOFT CONTINUES TO HINDER THE VERTICAL EXTENT OF 
CIRCULATION AND IS SHEARING DEEP CONVECTION SEVERAL DEGREES AHEAD
OF THE LOW LEVEL CIRCULATION CENTER (LLCC). BOTH KNES AND PGTW ARE 
FIXING A 2.0 DVORAK, WHICH CORRESPONDS TO 30 KNOTS. A SERIES OF 
MICROWAVE IMAGES, TO INCLUDE A 220947Z 85H TMI PASS, CONFIRM THAT 
THE LLCC HAS BEEN (AND CONTINUES TO BE) BIASED TO THE SOUTHEAST OF 
THE CENTRAL CONVECTION.
3. FORECAST REASONING
    A. THE FORECAST PHILOSOPHY HAS CHANGED SLIGHTLY SINCE THE 
PREVIOUS PROGNOSTIC REASONING MESSAGE. THE SYSTEM IS EXPECTED TO 
PEAK SOONER (TAU 36) AT A LOWER INTENSITY (45 KNOTS), THEN BEGIN 
TO WEAKEN DUE TO INCREASED VERTICAL WIND SHEAR IN THE LATER 
FORECAST PERIOD. THE FORECAST HAS ALSO BEEN SLOWED DOWN BEYOND
TAU 72.
    B. TD 02W IS FORECAST TO TRACK NORTHWESTWARD ALONG THE 
SOUTHWESTERN PERIPHERY OF THE LOW TO MID-LEVEL RIDGE TO THE 
NORTHEAST FOR THE FIRST 72 HOURS. MODEL GUIDANCE IS FAIRLY CONSISTENT
WITH A NORTHWESTWARD TRACK WITH THE EXCEPTION OF EGRR, A SOUTHERN 
OUTLIER, AND WBAR, A NORTHERN OUTLIER. THIS RIDGE WILL WEAKEN OVER 
THE NEXT 2 DAYS AS A MID-LATITUDE TROUGH, CURRENTLY ANALYZED OVER 
INTERIOR CHINA, PULLS OUT TO SEA AND DEEPENS. THE WILL ALLOW THE 
SHEAR GRADIENT TO MIGRATE FURTHER SOUTH AS THE PATTERN BECOMES MORE 
MERIDIONAL AND SHOULD LIMIT INTENSIFICATION BEYOND 45 KNOTS 
(ESPECIALLY IN LIGHT OF THE CURRENT PACE OF INTENSIFICATION).  
    C. BY TAU 72 THE TD WILL BEGIN TO WEAKEN DUE TO INCREASED 
VERTICAL WIND SHEAR ASSOCIATED WITH THE TROUGH IN PARA 3.B. THE 
SYSTEM WILL ALSO SLOW AS THE RIDGE CENTER WEAKENS AND PUSHES 
DOWNSTREAM. NEARLY ALL THE DYNAMICAL AIDS, WITH THE EXCEPTION OF 
EGRR, HINT AT WEAK RECURVATURE. GFS IS THE ONLY TRACKER THAT 
COMPLETES A CLASSIC RECURVATURE INTO THE MID-LATITUDES. IT IS LIKELY 
THAT THE SYSTEM WILL DISSIPATE DUE TO SHEAR BEFORE RECURVATURE CAN 
OCCUR.//
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