WDPN32 PGTW 090900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 25W (VAMCO) 
WARNING NR 001//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TROPICAL DEPRESSION 25W (VAMCO), LOCATED APPROXIMATELY 599 NM 
EAST-SOUTHEAST OF MANILA, PHILIPPINES, HAS TRACKED NORTHWESTWARD AT 
11 KNOTS OVER THE PAST SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE 
IMAGERY (MSI) DEPICTS FLARING DEEP CONVECTION, PRIMARILY STRETCHING 
ACROSS THE SOUTHERN HEMISPHERE OF A BROAD AND STILL SOMEWHAT 
ELONGATED LOW LEVEL CIRCULATION CENTER (LLCC). THE INITIAL POSITION 
IS PLACED WITH FAIR CONFIDENCE BASED ON ANALYSIS OF THE OUTER LOW-
LEVEL BANDS EVIDENT IN ANIMATED VISIBLE AND MSI. A PARTIAL 090514Z 
AMSR2 89 GHZ MICROWAVE IMAGE, SHOWS THE WELL-DEFINED OUTER LOW-LEVEL 
BANDING FEATURES, ANALYSIS OF WHICH PROVIDES ADDITIONAL WEIGHT TO 
THE INITIAL POSITION. THE INITIAL INTENSITY OF 25 KTS IS SET WITH 
FAIR CONFIDENCE BASED ON MULTI-AGENCY DVORAK CURRENT INTENSITY 
ESTIMATES OF T1.5 (25 KTS) FROM BOTH PGTW AND RJTD. A 090025Z ASCAT-
B AND 090114Z ASCAT-C SHOWED THE ELONGATED NATURE OF THE LLCC, WITH 
20-25 KNOT WINDS ALONG THE NORTHWESTERN AND SOUTHEASTERN PERIPHERY 
OF THE SYSTEM, WITH A POCKET OF HIGHER WINDS TO THE NORTHEAST. TD 
25W IS TRACKING NORTHWESTWARD ALONG THE SOUTHWESTERN PERIPHERY OF A 
SUBTROPICAL RIDGE (STR) POSITIONED TO THE NORTHEAST. THE SYSTEM IS 
TRACKING THROUGH AN ENVIRONMENT WHICH IS VERY FAVORABLE FOR 
DEVELOPMENT WITH WARM (29-30 CELSIUS) SEA SURFACE TEMPERATURES 
(SST), LOW (5-10 KTS) VERTICAL WIND SHEAR (VWS), HIGH (120-140 
KJ/CM^2) OHC AND A DEVELOPING UPPER-LEVEL POINT SOURCE PROVIDING 
STRONG EQUATORWARD AND MODERATE POLEWARD OUTFLOW. 
3. FORECAST REASONING.
   A. THIS IS THE FIRST PROGNOSTIC REASONING MESSAGE AND SETS THE 
FORECAST PHILOSOPHY.
   B. TD 25W WILL CONTINUE TO TRACK NORTHWESTWARD THROUGH TAU 12 AND 
SLOWLY TURN ONTO A WESTWARD TRACK BY TAU 48 AS THE STR BUILDS 
WESTWARD TO THE NORTH OF THE SYSTEM, BLOCKING FURTHER POLEWARD 
MOVEMENT. TD 25W IS FORECAST TO MAKE LANDFALL IN CENTRAL LUZON, 
ROUGHLY EAST OF MANILA, NEAR TAU 60, RAPIDLY TRACK ACROSS LUZON AND 
REEMERGE INTO THE SOUTH CHINA SEA BY TAU 72. OVERALL THE ENVIRONMENT 
IS HIGHLY CONDUCIVE TO INTENSIFICATION, WITH THE ONLY LIMITATION 
BEING THE TIME NEEDED TO CONSOLIDATE INTO A BETTER DEFINED 
CIRCULATION CENTER. ONCE THE SYSTEM BECOMES WELL CONSOLIDATED, 
WITHIN THE NEXT 6 TO 12 HOURS, IT IS EXPECTED TO BEGIN TO QUICKLY 
INTENSIFY TO 55 KNOTS BY TAU 24. A PERIOD OF RAPID INTENSIFICATION 
IS FORECAST BETWEEN TAUS 36 AND 48 AS THE SYSTEM TRACKS OVER WATERS 
WITH OHC VALUES APPROACHING 150-175 KJ/CM^2, VWS REMAINS VERY LOW 
AND THE UPPER-LEVEL ANTICYCLONE BECOMES VERTICALLY STACKED OVER THE 
LLCC, AND BEGINS TO TAP INTO A POLEWARD OUTFLOW CHANNEL. THE 
FORECAST CALLS FOR A PEAK INTENSITY OF 110 KNOTS AT TAU 48, BUT 
ADDITIONAL INTENSIFICATION IS POSSIBLE PRIOR TO LANDFALL. AS THE 
SYSTEM CROSSES LUZON, INTERACTION WITH THE RUGGED TERRAIN WILL 
INDUCE SIGNIFICANT WEAKENING, WITH THE SYSTEM FORECAST TO REEMERGE 
INTO THE SOUTH CHINA SEA AS A MINIMAL TYPHOON. NUMERICAL MODEL TRACK 
GUIDANCE IS IN TIGHT AGREEMENT THROUGH THE TURN WESTWARD, WITH 
DIFFERENT SOLUTIONS ON THE TIMING AND DEGREE OF THE TURN WESTWARD, 
LEADING TO A SPREAD OF 100NM AT TAU 48 WITH NAVGEM REPRESENTING THE 
POLEWARD EDGE OF THE ENVELOPE AND JGSM THE EQUATORWARD. THIS TIGHT 
AGREEMENT LENDS OVERALL GOOD CONFIDENCE IN THIS INITIAL PORTION OF 
THE JTWC FORECAST TRACK, LAID ON THE NORTHERN EDGE OF THE GUIDANCE 
ENVELOPE THROUGH TAU 48, THEN NEAR THE MULTI-MODEL CONSENSUS THROUGH 
TAU 72. INTENSITY GUIDANCE IS MORE MIXED, WITH THE COAMP-TC SHOWING 
VERY SLOW INTENSIFICATION AND A PEAK OF ONLY 55 KNOTS, WHILE HWRF 
SHOWS A PEAK OF 115 KNOTS AND THE REMAINDER OF THE GUIDANCE PACKAGE 
BEING CLOSER TO THE 85-90 KNOT RANGE. BASED ON THE ENVIRONMENTAL 
ANALYSIS, THE JTWC FORECAST IS WELL ABOVE THE CONSENSUS, AND CLOSELY 
TRACKS THE HWRF SOLUTION.  
   C. AFTER TAU 72, THE SYSTEM WILL CONTINUE TO TRACK WESTWARD 
THROUGH TAU 120 UNDER THE STEERING INFLUENCE OF THE DEEP-LAYER STR 
TO THE NORTH. AFTER REEMERGING OVER THE OPEN WATERS OF THE SOUTH 
CHINA SEA, THE SYSTEM WILL REINTENSIFY TO A PEAK OF 70 KNOTS UNDER 
MARGINALLY FAVORABLE ENVIRONMENTAL CONDITIONS. NUMERICAL MODEL 
GUIDANCE IS IN FAIR AGREEMENT WITH CROSS-TRACK SPREAD INCREASING TO 
215 NM AT TAU 120, WITH THE MAJORITY OF MODELS SUPPORTING THE 
WESTWARD TRACK, WHILE A GROUP CONSISTING OF NVGM, AFUM, HWRF AND THE 
UKMET ENSEMBLE SHOWING A SLIGHTLY MORE WEST-NORTHWESTWARD TRACK 
TOWARDS HAINAN ISLAND. IN LIGHT OF THE INCREASING UNCERTAINTY AND 
DISTINCT SEPARATION IN THE CONSENSUS MODELS, THERE IS OVERALL LOW 
CONFIDENCE IN THE EXTENDED FORECAST TRACK, WHICH LIES JUST SOUTH OF 
THE CONSENSUS TRACK, NEAR THE ECMWF SOLUTION.//
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