Friday, September 2, 2011

JTWC - Prognostic Reasoning for Tropical Cyclone Advisory 32 - Tropical Storm Talas

WDPN32 PGTW 020300
MSGID/GENADMIN/NAVMARFCSTCEN PEARL HARBOR HI/JTWC//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 15W (TALAS) WARNING NR
32//
RMKS/
1. FOR METEOROLOGISTS.
2. 12 HOUR SUMMARY AND ANALYSIS.
A. TROPICAL STORM (TS) 15W (TALAS), LOCATED APPROXIMATELY 280 NM
SOUTHEAST OF IWAKUNI, JAPAN, HAS TRACKED NORTH-NORTHWESTWARD AT 08
KNOTS OVER THE PAST SIX HOURS. TS 15W IS ZEROING IN ON OSAKA BAY AND
THE KANSAI REGION OF HONSHU WHILE MAINTAINING A STEADY INTENSITY.
RECENT ANIMATED MULTISPECTRAL SATELLITE IMAGERY SHOWS THE LOW LEVEL
CIRCULATION CENTER (LLCC) EXPANDING EVEN MORE. THE DIAMETER OF THE
OPEN AREA IS NOW 140 NM. THE SIZE OF THE LLCC AND THE UPPER LEVEL
CYCLONE HAVE PREVENTED CONVECTION FROM CONSOLIDATING OVER THE
SYSTEM. THE OUTER RAIN BANDS ARE BRINGING HEAVY PRECIPITATION TO
SHIKOKU AND THE WAKAYAMA PREFECTURE. COASTAL STATIONS ARE REPORTING
NEAR GALE FORCE WINDS, AND THE 011200Z SOUNDING FROM SHIONOMISAKI
(WAKAYAMA PENINSULA, WMO 47778) REVEALED 50 KNOT WINDS BEGINNING AT
ONE THOUSAND FEET. 20 KT SOUTHEASTERLIES HAVE SET IN AT TOKUSHIMA
AIRPORT (RJOS). A 011135Z ASCAT IMAGE CAPTURES THE EXPANSIVE NATURE
OF THE SYSTEM, SHOWING GALE FORCE WINDS EXTENDING OVER 200 NM
OUTWARDS IN THE NORTHERN SEMICIRCLE. A 012256Z SSMIS IMAGE COMPARED
TO PREVIOUS MICROWAVE IMAGERY INDICATES THE LOW LEVEL CONVECTIVE
BANDS ARE BECOMING MORE ELONGATED AND LESS CONCENTRIC AROUND THE
LLCC, AND THE HIGHER FREQUENCIES SHOW A SIGNIFICANT DROP-OFF IN DEEP
CONVECTION. THE CURRENT INTENSITY IS BASED ON A COMBINATION OF
SURFACE REPORTS, UPPER AIR SOUNDINGS FROM SHIONOMISAKI AND HAMAMATSU
AIR BASE, AND AN EARLIER ASCAT IMAGE RATHER THAN SUBJECTIVE DVORAK
ESTIMATES. THE EXPANSIVENESS OF TS 15W IS MAKING FOR DVORAK
ESTIMATES THAT ARE BELOW ACTUAL INTENSITY. ANIMATED WATER
VAPORIMAGERY REVEALS A WELL-DEVELOPED POLEWARD OUTFLOW CHANNEL ON
THE NORTHEAST QUADRANT AS THE STORM TAPS INTO AN UPPER LEVEL TROUGH.
THE TROUGH IS SUPPORTING A COLD FRONT THAT WILL COME INTO PLAY AFTER
THE STORM CROSSES HONSHU. VERTICAL WIND SHEAR REMAINS UNDER 10
KNOTS AND SEA SURFACE TEMPERATURE (SST) HAS INCREASED TO 28 DEGREES.
TS 15W IS BEING STEERED ALONG THE WESTERN FLANK OF A BLOCKING RIDGE
THAT HAS SET UP OVER WESTPAC. THE OMEGA BLOCK IS DRIVING TS 15W
TOWARDS OSAKA BAY AND THE KANSAI REGION OF HONSHU.
3. FORECAST REASONING.
A. THERE IS NO CHANGE TO THE FORECAST PHILOSOPHY.
B. TS 15W WILL CONTINUE STEERING ALONG THE WESTERN FLANK OF A
BLOCKING RIDGE THAT HAS SET UP OVER WESTPAC. THERE REMAINS A
REASONABLE CHANCE FOR MILD INTENSIFICATION BEFORE TS 15W FEELS THE
EFFECTS OF LAND INTERACTION. THE POLEWARD OUTFLOW CHANNEL IS WELL-
ESTABLISHED SO OUTFLOW WILL NOT CHANGE MUCH, BUT SST WILL INCREASE
ANOTHER DEGREE OR TWO AS THE STORM CROSSES THE KUROSHIO CURRENT. THE
BLOCK WILL DRIVE THE SYSTEM POLEWARD AND INTO THE SEA OF JAPAN NEAR
TAU 30, WHERE IT WILL HAVE A BRIEF PERIOD OF FAVORABLE CONDITIONS TO
RE-GROUP. NORTH OF 37 DEGREES LATITUDE, HOWEVER, TS 15W WILL
ENCOUNTER A SHARP INCREASE IN VERTICAL WIND SHEAR, A SHARP DROP IN
SEA SURFACE TEMPERATURE, AND INTERACTION WITH A BAROCLINIC BOUNDARY
IN A VERY BRIEF PERIOD. TS 15W WILL THEN GO THROUGH A RAPID
EXTRATROPICAL TRANSITION PROCESS (XTT) WHILE ACCELERATING TO THE
NORTHEAST. THICKNESS PROGS ARE SPEEDING UP THE PROCESS, INDICATING
XTT COMPLETION NEAR 40N, SHORTLY AFTER TAU 48. THE UPSTREAM ENERGY
ASSOCIATED WITH THE ENCROACHING MID-LATITUDE SYSTEM FORESHADOWS A
VIGOROUS TRANSITION INTO AN EXPANSIVE, GALE FORCE MID-LATITUDE LOW.
ALTHOUGH MOST MODEL GUIDANCE IS COMING INTO BETTER AGREEMENT AND
MOVING THE TRACK EASTWARD, THEY ARE STILL SHOWING A TENDENCY TO
STEER THE VORTEX TOWARDS THE 500 MB HEIGHT FALLS, A COMMON
OCCURRENCE DURING XTT. THE ONLY GUIDANCE HANDLING THE XTT PROCESS
CAPABLY IS ECMWF. THE JTWC FORECAST STAYS WELL RIGGHT OF, AND FASTER
THAN CONSENSUS, AND CLOSE TO ECMWF.//

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