WDPN31 PGTW 190900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 19W 
(NINETEEN) WARNING NR 002//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TROPICAL DEPRESSION (TD) 19W (NINETEEN), LOCATED
APPROXIMATELY 427 NM EAST OF MANILA, PHILIPPINES, HAS 
TRACKED WEST-NORTHWESTWARD AT 13 KNOTS OVER THE PAST 
SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE IMAGERY 
(MSI) DEPICTS A BROAD SYSTEM, WITH WELL DEFINED LOW 
LEVEL SPIRAL BANDS OF DEEP CONVECTION LYING OUTSIDE OF 
A MOAT OF LITTLE TO NO CONVECTION SURROUNDING AN 
OBSCURED LOW LEVEL CIRCULATION CENTER (LLCC). THE 
INITIAL POSITION IS PLACED WITH FAIR CONFIDENCE BASED 
ON ANALYSIS OF THE LOW LEVEL BANDS, WITH SUPPORT FROM 
A 190456Z AMSR2 36GHZ AND 89GHZ COMPOSITE MICROWAVE 
IMAGE. THE INITIAL INTENSITY OF 30 KNOTS IS ASSESSED 
WITH HIGH CONFIDENCE BASED ON MULTI-AGENCY DVORAK 
CURRENT INTENSITY ESTIMATES OF T2.0 (30 KNOTS) FROM 
PGTW AND KNES) AND T1.5 (25 KNOTS) FROM RJTD, AS WELL 
AS AN ADVANCED DVORAK TECHNIQUE ESTIMATE OF T1.8 (28 
KNOTS), AND A SATELLITE CONSENSUS ESTIMATE OF 38 KNOTS. 
TD 19W IS TRACKING ALONG THE SOUTHERN PERIPHERY OF A 
SUBTROPICAL RIDGE EXTENDING SOUTHWESTWARD FROM A CENTER 
NEAR 30N 155E TO FAR NORTHERN VIETNAM. THE SYSTEM IS 
TRACKING THROUGH A GENERALLY FAVORABLE ENVIRONMENT WITH 
WARM SSTS (29-30 DEG CELSIUS), LOW VWS (10-15 KNOTS) AND
MODERATE UPPER-LEVEL OUTFLOW ON THE DIVERGENT SOUTHWEST
QUADRANT OF AN UPPER LEVEL ANTICYCLONE.  
3. FORECAST REASONING.
   A. NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE 
PREVIOUS PROGNOSTIC REASONING MESSAGE.
   B. TD 19W WILL CONTINUE TO TRACK GENERALLY WEST-
NORTHWESTWARD ALONG THE PERIPHERY OF THE STEERING STR 
OVER THE NEXT 36 HOURS AS IT APPROACHES AND THEN CROSSES
CENTRAL LUZON. AFTER REEMERGING OVER WATER JUST AFTER TAU 
36, THE SYSTEM IS FORECAST TO TAKE ON A SLIGHTLY MORE 
NORTHWESTERLY COURSE FOR SHORT PERIOD TOWARDS A WEAKNESS 
IN THE STEERING RIDGE, BEFORE AGAIN RESUMING A WESTWARD 
TRACK BY TAU 96. TD 19W IS FORECAST TO STEADILY INTENSIFY 
TO 45 KNOTS BEFORE MAKING LANDFALL ON THE CENTRAL LUZON 
COASTLINE. THE SYSTEM WILL MAINTAIN INTENSITY AT 45 KNOTS, 
OR EVEN SLIGHTLY WEAKEN BEFORE RESUMING INTENSIFICATION 
AFTER TAU 48 OVER THE OPEN WATERS OF THE SOUTH CHINA SEA.
TD 19W IS FORECAST TO REACH A PEAK INTENSITY OF 60 KNOTS 
BY TAU 72 AS MARGINAL UPPER LEVEL OUTFLOW IS OFFSET BY LOW 
TO MODERATE (15-20 KNOTS) VWS AND WARM SSTS (29 DEG CELSIUS). 
NUMERICAL TRACK GUIDANCE IS IN MODERATE AGREEMENT WITH 115 
NM SPREAD AT TAU 12 INCREASING TO 255 NM BY TAU 72, WITH 
NAVGEM REPRESENTING THE NORTHERN OUTLIER AND THE ECMWF 
ENSEMBLE TRACKER BEING THE SOUTHERN OUTLIER. THE JTWC TRACK 
FORECAST LIES ALONG THE SOUTHERN SIDE OF THE GUIDANCE 
ENVELOPE THROUGH TAU 48. DUE TO THE INCREASING SPREAD 
IN THE GUIDANCE ENVELOPE, THERE IS OVERALL LOW CONFIDENCE 
IN THIS PORTION OF THE JTWC FORECAST TRACK. ADDITIONALLY, 
THERE EXISTS AN ALTERNATE SCENARIO, IN WHICH THE WEAKNESS 
IN THE STEERING RIDGE IS STRONGER AND LAST LONGER THAN 
CURRENTLY FORECAST, LEADING TO A MORE NORTHWARD AND SLOWER 
JOB IN THE TRACK BETWEEN TAUS 36 AND 72. THE NAVGEM AND 
UKMET ENSEMBLE GENERALLY INDICATE THIS SCENARIO, SHOWING 
A SHORT PERIOD OF MORE NORTHWARD MOVEMENT BEFORE RESUMING 
A WESTWARD TRACK BY TAU 96. THE HWRF TRACKER REPRESENTS 
THE OUTLIER IN THE FORECAST TRACK, TAKING THE SYSTEM 
COMPLETELY INTO THE WEAKNESS IN THE RIDGE TOWARDS HONG KONG 
THROUGH TAU 120. AT THIS TIME HOWEVER, THE WEAKNESS IN THE 
RIDGE DOES NOT APPEAR TO BE STRONG OR LONG LASTING ENOUGH 
TO LEAD TO A NORTHWARD TRACK FORECAST.  
   C. IN THE EXTENDED FORECAST, TD 19W IS EXPECTED TO TRACK
WESTWARD AND THEN WEST-SOUTHWESTWARD AS THE PRIMARY STEERING 
MECHANISM SHIFTS TO A DEVELOPING STR LOCATED THE NORTHWEST 
OF THE SYSTEM. AS THE SYSTEM MOVES WEST AND COMES UNDER THE 
INFLUENCE OF THE STR TO THE NORTHWEST, UPPER LEVEL OUTFLOW 
BECOMES CONVERGENT OVER TOP OF THE SYSTEM WHILE VWS WILL 
BEGIN TO INCREASE TO 20-30 KNOTS, OFFSETTING THE CONTINUED 
WARM SSTS, AND LEADING TO A STEADY WEAKENING TREND. NUMERICAL 
MODELS GENERALLY AGREE ON THE WESTWARD TRACK BUT WITH ACROSS 
TRACK SPREAD INCREASING TO NEARLY 300 NM AT TAU 120, WITH 
NAVGEM TAKING THE SYSTEM OVER HAINAN, WHILE GFS TAKES THE 
SYSTEM INLAND OVER CENTRAL VIETNAM. AS DISCUSSED PREVIOUSLY, 
THE HWRF MODEL IS THE NOTABLE OUTLIER, TAKING THE SYSTEM 
NORTHWARD TOWARDS HONG KONG BY TAU 120 BUT THIS REPRESENTS 
THE ALTERNATE SCENARIO AND ALL THE REMAINDER OF THE MODEL 
GUIDANCE SHOWS A GENERALLY WESTWARD TRACK THROUGH TAU 120. 
DUE TO POSSIBILITY OF THE ALTERNATE SCENARIO AND THE 
INCREASED MODEL SPREAD EVEN WHEN DISCOUNTING THE HWRF 
SOLUTION, THERE REMAINS LOW CONFIDENCE IN THIS PORTION 
OF THE JTWC FORECAST TRACK.//
NNNN