WDPN33 PGTW 112100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 18W (EIGHTEEN) 
WARNING NR 001//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TROPICAL DEPRESSION (TD) 18W (EIGHTEEN), LOCATED APPROXIMATELY 237
 NM NORTHWEST OF MANILA, PHILIPPINES, HAS TRACKED WEST-NORTHWESTWARD 
AT 07 KNOTS (KTS) OVER THE PAST SIX HOURS.  ANIMATED ENHANCED 
INFRARED SATELLITE IMAGERY REVEALS CONVECTIVE BANDING WRAPPING INTO A 
LOW LEVEL CIRCULATION CENTER (LLCC) OBSCURED BY FLARING CONVECTION 
OVERHEAD. AN 111759Z AMSR2 89 GHZ MICROWAVE IMAGE DEPICTS FRAGMENTED 
CONVECTIVE BANDING NORTH OF A CONSOLIDATING LLCC, LENDING GOOD 
CONFIDENCE TO THE INITIAL POSITION. THE INITIAL INTENSITY IS SET AT 
25 KTS BASED ON MULTI-AGENCY DVORAK CURRENT INTENSITY ESTIMATES OF 
T1.0-1.5 (25 KTS) BY PGTW, KNES, AND RJTD AND RECENT ASCAT DATA. TD 
18W IS TRACKING THROUGH A FAVORABLE ENVIRONMENT CONSISTING OF GOOD 
EQUATORWARD OUTFLOW, LOW (<10 KT) VERTICAL WIND SHEAR (VWS), AND HIGH 
(29-30 CELSIUS) SEA SURFACE TEMPERATURES (SST). UNDER THE INFLUENCE 
OF A DEEP-LAYERED SUBTROPICAL RIDGE (STR) TO THE NORTH, TD 18W IS 
TRACKING GENERALLY WESTWARD ALONG ITS SOUTHERN PERIPHERY. 
3. FORECAST REASONING.
   A. THIS IS THE FIRST PROGNOSTIC REASONING MESSAGE AND SETS THE 
FORECAST PHILOSOPHY.
   B. THE AFOREMENTIONED STR WILL ACT AS THE STEERING MECHANISM 
THROUGHOUT THE ENTIRE FORECAST PERIOD. THROUGH TAU 48, TD 18W IS 
FORECAST TO TRACK GENERALLY WESTWARD AS IT STEADILY STRENGTHENS TO A 
PEAK INTENSITY OF 60 KTS BY TAU 36 DUE TO CONTINUED FAVORABLE 
ENVIRONMENTAL CONDITIONS. AFTERWARDS, THE SYSTEM WILL SHIFT TO A 
WEST-NORTHWESTWARD TRACK THROUGH TAU 72, MAINTAINING INTENSITY 
THROUGH TAU 48 AND THEN GRADUALLY WEAKENING AS IT TRACKS OVER HAINAN 
AND INTO THE GULF OF TONKIN. THROUGH TAU 72, NUMERICAL MODEL GUIDANCE 
IS IN GOOD AGREEMENT WITH THE EXCEPTION OF NAVGEM WHICH PRESENTS A 
SOUTHERLY OUTLIER. THERE IS ONLY 50 NM OF TRACK SPREAD AMONG THE 
MAJORITY OF THE MODELS AT TAU 48, LENDING GOOD CONFIDENCE TO THE JTWC 
NEAR-TERM FORECAST TRACK.
   C. IN THE EXTENDED RANGE, TD 18W WILL TRACK GENERALLY WESTWARD 
ALONG THE PERIPHERY OF THE AFOREMENTIONED STR AS IT MAKES LANDFALL IN 
NORTHERN VIETNAM AFTER TAU 72. BY TAU 72, NUMERICAL MODEL SPREAD 
INCREASES TO 100 NM, PLACING SOME UNCERTAINTY IN THE EXACT LOCATION 
WHERE TD 18W WILL MAKE LANDFALL; CURRENT GUIDANCE DEPICTS LANDFALL 
SOUTH OF HANOI, VIETNAM. AFTERWARDS, THE SYSTEM WILL STEADILY WEAKEN 
DUE TO INTERACTION WITH THE RUGGED TERRAIN AND DISSIPATION OVER LAND 
IS ANTICIPATED BY TAU 96. THE JTWC FORECAST TRACK LIES NEAR THE 
MULTI-MODEL CONSENSUS; HOWEVER, DUE TO THE INCREASING MODEL SPREAD IN 
THE EXTENDED RANGE, THERE IS OVERALL FAIR CONFIDENCE IN THE JTWC 
FORECAST TRACK.//
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