Tropical Storm NOUL Advisory Sa, 15.09.

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 13W (THIRTEEN)
WARNING NR 001//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
TROPICAL DEPRESSION 13W (THIRTEEN), LOCATED APPROXIMATELY 165 NM SOUTHWEST
OF MANILA, PHILIPPINES, HAS TRACKED WESTWARD AT 14 KNOTS OVER THE PAST SIX
HOURS. ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS
DISORGANIZED, DEEP CONVECTION OBSCURING A LOW LEVEL CIRCULATION CENTER
(LLCC). THE INITIAL POSITION IS PLACED WITH HIGH CONFIDENCE BASED ON
THE POSITION OF THE LLCC IN THE EIR LOOP AS WELL AS IN A 151349Z ASCAT-B
PASS. THE INITIAL INTENSITY OF 25 KTS IS ALSO PLACED WITH HIGH CONFIDENCE
AND IS HEDGED SLIGHTLY HIGHER THAN MULTI-AGENCY DVORAK CURRENT INTENSITY
ESTIMATES OF T1.0 (PGTW, 25 KTS) AND T1.5 (RJTD, 25 KTS) BASED ON THE 30 KTS
WINDS PRESENT IN THE AFOREMENTIONED SCATTEROMETRY DATA. TD 13W IS CURRENTLY
TRACKING ALONG THE SOUTHERN PERIPHERY OF THE SUBTROPICAL RIDGE (STR) THAT IS
POSITIONED TO THE NORTHEAST AND THROUGH AN ENVIRONMENT THAT IS FAVORABLE FOR
FURTHER DEVELOPMENT WITH VERY WARM (30-32 CELSIUS) SEA SURFACE TEMPERATURES
(SST) AND MODERATE EQUATORWARD OUTFLOW ALOFT OFFSET SLIGHTLY BY MODERATE
(15-20 KTS) VERTICAL WINDSHEAR (VWS) ALONG THE WESTERN PERIPHERY OF THE
SYSTEM.
3. FORECAST REASONING.
   A. THIS IS THE INITIAL PROGNOSTIC REASONING MESSAGE FOR THIS SYSTEM
AND SETS THE FORECAST PHILOSOPHY.
   B. IN THE NEAR-TERM, TD 13W WILL TRACK GENERALLY WEST-NORTHWESTWARD
OVER THE WARM WATERS OF THE SOUTH CHINA SEA TOWARDS TO COAST OF VIETNAM
UNDER THE STEERING INFLUENCE OF THE STR POSITIONED TO THE NORTHEAST. THE
SYSTEM WILL CONTINUE TO INTENSIFY TO 40 KTS BY TAU 12 AS A RESULT OF
CONTINUED VERY WARM SSTS, SUFFICIENT UPPER LEVEL OUTFLOW AND LOW TO
MODERATE (10-15 KTS) VERTICAL WIND SHEAR. AFTER TAU 12, THE SYSTEM WILL
BEGIN A MORE MODERATED INTENSIFICATION DUE TO MODERATE (15-20 KTS) VWS
AND CONVERGENT FLOW DUE TO THE DEEP EASTERLY FLOW ALOFT ALONG THE NORTHERN
PERIPHERY OF THE SYSTEM, LEADING TO A PEAK INTENSITY OF 70 KTS BY TAU 48.
THEREAFTER, THE SYSTEM WILL WEAKEN SLIGHTLY DUE TO CONTINUED MODERATE VWS
AND CONVERGENT FLOW ALONG THE NORTHERN PERIPHERY TO AN INTENSITY OF 65 KTS
BY TAU 72. NUMERICAL MODEL SOLUTIONS ARE IN FAIR AGREEMENT BOTH ALONG AND
ACROSS TRACK WITH A MAXIMUM SPREAD OF 130 NM AT TAU 48 THAT DECREASES TO
105 NM BY TAU 72. THIS SPREAD IS LIKELY THE RESULT OF THE MODELS RESOLVING
AN INCOMING SHORTWAVE TROUGH PROPAGATING FROM THE WEST THAT WILL CAUSE THE
STEERING RIDGE TO RECEDE TO THE EAST BETWEEN TAU 48 AND TAU 72. THIS FAIR
AGREEMENT IN MODEL SOLUTIONS LENDS OVERALL FAIR CONFIDENCE IN THIS INITIAL
PORTION OF THE JTWC FORECAST TRACK.
   C. IN THE EXTENDED PERIOD, THE SYSTEM WILL CONTINUE TO TRACK GENERALLY
WEST-NORTHWESTWARD AND REACH LANDFALL ALONG THE VIETNAM COAST JUST AFTER
TAU 72. THEREAFTER THE SYSTEM WILL BEGIN TO WEAKEN RAPIDLY DUE TO CONTINUED
MODERATE VWS AND INTERACTION WITH THE UNDERLYING TERRAIN. BY TAU 96 THE
SYSTEM INTENSITY WILL WEAKEN TO 30 KTS AND BEGIN TO DISSIPATE OVER LAND. BY
TAU 120 CONTINUED TERRAIN INTERACTIONS WILL LEAD TO DISSIPATION OVER LAND.
NUMERICAL MODEL SOLUTIONS DIVERGE TO A GREATER EXTENT IN THIS EXTENDED
PORTION OF THE FORECAST WITH A MAXIMUM ACROSS TRACK SPREAD OF 260 NM BY TAU
96. THIS HIGHER SPREAD IN TRACK GUIDANCE LENDS ONLY FAIR CONFIDENCE TO THE
OVERALL JTWC FORECAST TRACK WHICH IS PLACED ALONG THE MULTI-MODEL CONSENSUS.//
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