Tropical Storm DUJUAN Advisory vie, 19-02

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 01W (ONE) WARNING
NR 005//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TROPICAL STORM (TS) 01W (DAJUAN), LOCATED APPROXIMATELY 787 NM
EAST-SOUTHEAST OF MANILA, PHILIPPINES, HAS TRACKED NORTHWESTWARD AT
05 KNOTS
OVER THE PAST SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE IMAGERY
REVEALS A FULLY EXPOSED, WELL-DEFINED LOW LEVEL CIRCULATION CENTER
(LLCC), WITH FLARING DEEP CONVECTION WITH OVERSHOOTING TOPS SHEARED
TO THE WEST OF THE LLCC, LENDING HIGH CONFIDENCE TO THE INITIAL
POSITION. THE INITIAL INTENSITY IS ASSESSED AT 35 KNOTS WITH HIGH
CONFIDENCE BASED ON DVORAK CURRENT INTENSITY ESTIMATES BETWEEN T2.0
(30 KTS, RJTD AND KNES) AND T2.5 (35 KTS, PGTW) AND AN ADT ESTIMATE
OF 2.5 (35 KTS). UPPER-LEVEL ANALYSIS INDICATES A MARGINAL
ENVIRONMENT WITH MODERATE (15-20 KNOTS) EASTERLY VERTICAL WIND SHEAR
(VWS) OFFSET BY ROBUST DIFFLUENT POLEWARD OUTFLOW. SST VALUES REMAIN
CONDUCIVE AT 29-30C. TS 01W IS MOVING SLOWLY WESTWARD IN A GENERALLY
WEAK STEERING PATTERN, COCOONED WITHIN A COL AREA BETWEEN A
SUBTROPICAL RIDGE (STR) TO THE NORTHEAST AND A SECOND TO THE
SOUTHWEST.
3. FORECAST REASONING.
   A. THERE IS NO SIGNIFICANT CHANGE IN THE FORECAST PHILOSOPHY FROM
THE PREVIOUS PROGNOSTIC REASONING MESSAGE.
   B. TS 01W IS LOCATED WITHIN A WEAK STEERING ENVIRONMENT SOUTH OF
A BREAK IN THE SUBTROPICAL RIDGE (STR) RESULTING FROM THE PRESENCE
OF A MAJOR
SHORTWAVE TROUGH EXTENDING FROM JAPAN TO EAST OF TAIWAN. OVER THE
NEXT 36 HOURS, THE SHORTWAVE TROUGH WILL MOVE TO THE NORTHEAST AND
FILL, ALLOWING FOR THE STR TO THE EAST TO BUILD IN TO THE NORTHEAST
OF TS 01W, ALLOWING THE SYSTEM TO MOVE SLOWLY WESTWARD THROUGH TAU
36. AFTER TAU 48, THE STR AXIS REORIENTS SLIGHTLY TO A MORE
NORTHWEST-SOUTHEAST ORIENTATION, AND IN RESPONSE TS 01W WILL TURN TO
A MORE WEST-NORTHWEST TRACK THROUGH TAU 72. LANDFALL IS EXPECTED
NEAR TAU 60 ALONG THE FAR NORTHEAST COAST OF MINDANAO. NUMERICAL
MODEL GUIDANCE IS IN FAIR AGREEMENT THROUGH TAU 48, WITH INCREASING
UNCERTAINTY BY TAU 72. THE UKMET DETERMINISTIC AND ENSEMBLE
SOLUTIONS CONTINUE TO SHOW AN UNLIKELY POLEWARD TRACK TO THE EAST OF
THE PHILIPPINES, WHILE THE GFS SOLUTION SHOWS AN EQUALLY UNLIKELY
DUE TO WEST TRACK. DISCOUNTING THE OUTLIERS, THE REMAINDER OF THE
CONSENSUS MEMBERS LIE CLOSE TO THE CONSENSUS MEAN, WITH A 150NM
SPREAD IN SOLUTIONS AT TAU 72. AS DISCUSSED EARLIER, VWS IS
CURRENTLY DOMINATING THE SYSTEM. HOWEVER, VWS IS EXPECTED TO WEAKEN
SLIGHTLY OVER THE NEXT DAY OR SO, WHICH WILL ALLOW THE SYSTEM TO
REESTABLISH CORE CONVECTION, ENABLING A SLOW BUT STEADY
INTENSIFICATION TO A PEAK OF 50 KNOTS BY TAU 48. THERE IS
CONSIDERABLE UNCERTAINTY HOWEVER IN THE INTENSIFICATION FORECAST DUE
TO THE STEADY EASTERLY VWS AND HOW MUCH THE STRONG POLEWARD OUTFLOW
WILL OFFSET THIS SHEAR.
   C. THE SYSTEM IS FORECAST TO CONTINUE TRACKING ALONG THE WESTERN
BOUNDARY OF THE DEEP-LAYER STR LOCATED TO THE EAST THROUGH THE
EXTENDED FORECAST PERIOD. BY TAU 72 THE SYSTEM IS EXPECTED TO BE IN
THE BOHOL SEA, AND WILL TRACK NORTHWESTWARD OVER THE MAJOR ISLANDS
OF THE SOUTHWEST PHILIPPINES, REEMERGING INTO THE INTO THE NORTHERN
SULU SEA BY TAU 96, AND INTO THE SOUTH CHINA SEA BEFORE TAU 120. THE
COMBINED EFFECTS OF TERRAIN INTERACTION, INCREASING VWS, DECREASED
UPPER-LEVEL OUTFLOW AND THE ENTRAINMENT OF DRIER AIR WILL WEAKEN THE
SYSTEM TO 25 KNOTS BY TAU 120. EVEN WHEN DISCOUNTING THE UKMET,
UKMET ENSEMBLE SHOWING THE UNLIKELY POLEWARD TRACK, AND THE GFS
DEPICTING A STRAIGHT WESTERLY TRACK, NUMERICAL MODEL GUIDANCE IS IN
POOR AGREEMENT AFTER TAU 72, WITH A 450NM SPREAD IN MODEL SOLUTIONS
BY TAU 120. THE JTWC FORECAST TRACK REMAINS CONSISTENT WITH THE
PREVIOUS FORECAST AND LIES NEAR THE ECMWF SOLUTION. OVERALL, THERE
IS POOR CONFIDENCE IN THE JTWC FORECAST TRACK, WHICH LIES SOUTH OF
THE MULTI-MODEL CONSENSUS, NEAR THE ECMWF SOLUTION.//
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