Tropical Storm MAYSAK Advisory Sat Aug 29

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 10W (MAYSAK)
WARNING NR 02//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TROPICAL DEPRESSION (TD) 10W (MAYSAK), LOCATED APPROXIMATELY
610 NM SOUTH OF KADENA AB, HAS TRACKED WEST-SOUTHWESTWARD AT 08
KNOTS OVER THE PAST SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE
IMAGERY (MSI) DEPICTS A DEVELOPING LOW LEVEL CIRCULATION CENTER
(LLCC) PARTIALLY OBSCURED BY DEEP CONVECTION OVER THE WESTERN
SEMICIRCLE, AND FLARING CONVECTION OVER THE EASTERN SEMICIRCLE. THE
INITIAL POSITION IS PLACED WITH FAIR CONFIDENCE BASED ON THE
PARTIALLY OBSCURED LLCC IN THE MSI LOOP AND THE LOW LEVEL FEATURES
PRESENT IN THE MICROWAVE IMAGERY FROM A 280513Z ATMS PASS. THE
INITIAL INTENSITY OF 30 KTS IS PLACED WITH HIGH CONFIDENCE BASED ON
MULTIAGENCY DVORAK CURRENT INTENSITY ESTIMATES OF T2.0 (30 KTS, PGTW AND
RJTD) AND THE 30 KTS WINDS DEPICTED IN BOTH A 280033Z ASCAT-B
AND 280125Z ASCAT-C PASS THAT ARE POSITIONED TO THE SOUTHWEST OF THE
LOW LEVEL CIRCULATION FEATURE. THE WINDFIELD IN THE SCATTEROMETRY
DATA ALSO CONSTRAINS THE INITIAL POSITION, HOWEVER THE LOW LEVEL
CIRCULATION IN THE DATA REMAINS ELONGATED ALONG THE WEST TO EAST
AXIS. ENVIRONMENTAL CONDITIONS ARE CONDUCIVE FOR FURTHER DEVELOPMENT
WITH DIVERGENT EQUATORWARD OUTFLOW AND VERY WARM (30-31 CELSIUS) SEA
SURFACE TEMPERATURES (SST) OFFSET SLIGHTLY BY MODERATE (15-20 KTS)
VERTICAL WIND SHEAR (VWS) AND CONVERGENT FLOW ALOFT TO THE NORTH OF
THE SYSTEM STEMMING FROM AN INCOMING TROPICAL UPPER TROPOSPHERIC TROUGH
(TUTT) CELL TO THE EAST. OCEAN HEAT CONTENT IS VERY HIGH (GREATER THAN
125 JOULES PER SQUARE CENTIMETER). THE SYSTEM IS TRACKING SLOWLY IN A
WEAK STEERING ENVIRONMENT INDUCED BY AN EXTENSION OF A NEAR EQUATORIAL
RIDGE POSITIONED TO THE SOUTH AND EAST OF THE SYSTEM CENTER THAT EXTENDS
FROM THE PHILIPPINES EASTWARD ALONG 10 DEGREES NORTH LATITUDE, A STRONG
SUBTROPICAL RIDGE (STR) TO THE NORTH AND A DEEP-LAYER SUBTROPICAL LOW
CENTERED NEAR THE NORTHERN MARIANAS.
3. FORECAST REASONING.
   A. NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE PREVIOUS PROGNOSTIC
REASONING MESSAGE.
   B. TD 10W WILL CONTINUE ITS SLOW, GENERALLY WESTWARD TRACK UNDER THE
INFLUENCE OF THE CURRENT WEAK STEERING PATTERN THROUGH TAU 12. STEADY
INTENSIFICATION TO 50 KTS WILL TAKE PLACE DURING THIS TIME AS THE SYSTEM
TRACKS OVER VERY WARM WATERS AND THROUGH CONTINUED MODERATE VWS AND
CONVERGENT FLOW ALOFT TO THE NORTH FROM THE AFOREMENTIONED TUTT CELL.
DECREASING VWS FROM TAU 12 TO TAU 24, COUPLED WITH THE WARM SST AND
AND CONTINUED DIVERGENT EQUATORWARD OUTFLOW, WILL ALLOW FOR FURTHER
INTENSIFICATION TO 50 KTS BY TAU 24. AFTER THIS TIME, THE CONVERGENT FLOW
FROM THE TUTT CELL WILL BECOME DIVERGENT AS THE THE CELL PROPAGATES
WESTWARD. BETWEEN TAU 24 AND TAU 36, A REORIENTATION OF THE STEERING
RIDGES WILL ALSO TAKE PLACE WITH THE NER MOVING NORTHWARD AND REORIENTING
INTO A NORTH-SOUTH ORIENTATED RIDGE AXIS ALONG ROUGHLY THE 140 EAST
LONGITUDE LINE, RESULTING IN A GENERALLY NORTHWARD TRACK BETWEEN THESE
TIMES. AT TAU 36 THE ENHANCED OUTFLOW FROM THE TUTT CELL, ALONG WITH THE
CONTINUED HIGH OCEAN HEAT CONTENT, VERY WARM SSTS AND LOW (5-10 KTS) VWS
WILL ALLOW THE SYSTEM TO INTENSIFY, POSSIBLY RAPIDLY, FROM TAU 36 TO TAU
48 AT WHICH TIME THE SYSTEM WILL REACH AN INTENSITY OF 80 KTS. AFTER THIS
TIME, THE SYSTEM WILL BEGIN TO TRACK ALONG THE PERIPHERY OF THE SUBTROPICAL
RIDGE TO THE EAST, RESULTING IN A NORTH-NORTHWESTWARD TRACK. THE ENVIRONMENT
IS EXPECTED TO REMAIN VERY FAVORABLE FOR FURTHER INTENSIFICATION AND WILL
RESULT IN FURTHER INTENSIFICATION TO 100 KTS BY TAU 72. NUMERICAL MODEL
SOLUTIONS ARE IN POOR AGREEMENT ON THE TIMING OF THE STEERING RIDGE
REPOSITIONING, WHICH LEADS TO A 255 NM CROSS TRACK SPREAD IN SOLUTIONS BY
TAU 72. THIS LARGE SPREAD IN SOLUTIONS LENDS OVERALL FAIR CONFIDENCE IN THE
INITIAL PORTION OF THE JTWC FORECAST TRACK.
   C. IN THE EXTENDED PERIOD, THE AFOREMENTIONED RIDGE COMPLEX TO THE
EAST WILL REORIENT ONCE AGAIN, DEEPENING AFTER TAU 72, AND BECOME THE
PRIMARY STEERING MECHANISM OF THE STORM. THIS WILL LEAD TO A GENERALLY
NORTHWESTWARD TRACK INITIALLY, AND THEN TO A NORTHWARD TRACK AS TD 10W
APPROACHES THE SUBTROPICAL RIDGE AXIS. TD 10W IS FORECAST TO REACH PEAK
INTENSITY OF 110 KNOTS AT TAU 96 UNDER VERY FAVORABLE CONDITIONS OF LOW
VWS, ROBUST, DIVERGENT POLEWARD OUTFLOW AND VERY WARM SSTS. AS THE SYSTEM
ENTERS THE EAST CHINA SEA, IT IS FORECAST TO WEAKEN SLIGHTLY, AS COOLER
SSTS IN THE WAKE OF THE PASSAGE OF TY 09W THROUGH THE AREA AND INCREASING
VWS, WILL OFFSET STRONG POLEWARD OUTFLOW INTO THE BASE OF AN APPROACHING
MID-LATITUDE TROUGH. THIS SLIGHT WEAKENING WILL BRING THE INTENSITY DOWN
TO 100 KTS BY TAU 120. NUMERICAL MODEL SOLUTIONS MAINTAIN A NEARLY 255 NM
CROSS TRACK SPREAD THROUGH THE REMAINDER OF THE FORECAST. ALONG TRACK
CROSS SPREAD HAS IMPROVED SINCE THE LAST SET OF NUMERICAL MODEL
CALCULATIONS, WITH AN AVERAGE 120 NM SPREAD BETWEEN TAU 72 AND TAU 120.
THE JTWC FORECAST TRACK LIES WEST OF THE MULTI-MODEL CONSENSUS THROUGH TAU
72, FAVORING THE ECMWF SOLUTION, THEN LIES VERY CLOSE TO THE CONSENSUS,
ALBEIT WITH A FASTER TRACK, THROUGH TAU 120. DUE TO THE SPREAD IN MODEL
SOLUTIONS AND UNCERTAINTY IN THE TIMING OF STEERING RIDGE REPOSITIONING,
THE OVERALL JTWC FORECAST TRACK IS PLACED WITH OVERALL FAIR CONFIDENCE.//
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