Sunday, September 4, 2011

JTWC - Prognostic Reasoning Tropical Cyclone Advisory 04 - Tropical Storm 16W

WDPN31 PGTW 040300
MSGID/GENADMIN/NAVMARFCSTCEN PEARL HARBOR HI/JTWC//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 16W WARNING NR 04//
RMKS/
1. FOR METEOROLOGISTS.
2. 12 HOUR SUMMARY AND ANALYSIS.
A. TROPICAL STORM (TS) 16W, LOCATED APPROXIMATELY 595 NM EAST-
NORTHEAST OF IWO TO, JAPAN, CONTINUED TO ACCELERATE AND TRACKED
NORTHWARD AT 35 KTS OVER THE PAST SIX HOURS. ANIMATED INFRARED
SATELLITE IMAGERY SHOWS THAT CONVECTIVE BANDS HAVE BECOME FRAGMENTED
AND DETACHED BEHIND THE MAIN AREA OF DEEP CENTRAL CONVECTION.
HOWEVER, ANIMATED MULTISPECTRAL IMAGERY SHOWS THE LOW LEVEL
CIRCULATIN CENTER REMAINS INTACT ALTHOUGH PARTIALLY EXPOSED AND
LAGGING BEHIND THE MAIN CONVECTION. THIS IS EVIDENT ON A 032314Z
METOPA MICROWAVE IMAGE. THE INITIAL POSITION WAS BASED ON THE ABOVE
ANIMATIONS AND FROM THE MICROWAVE IMAGE WITH HIGH CONFIDENCE. THE
INITIAL INTENSITY IS SUPPORTED BY DVORAK ESTIMATES FROM PGTW, RJTD
AND KNES. UPPER LEVEL ANALYSIS INDICATES THE SYSTEM IS JUST TO THE
EAST OF A TROPICAL UPPER TROPOSPHERIC TROUGH (TUTT) AND TO THE WEST
OF AN ANTICYCLONE THAT IS ENHANCING NORTHEASTWARD OUTFLOW, ALBEIT
IN AN AREA OF MODERATE (15-20 KT) VERTICAL WIND SHEAR (VWS). THE
TUTT LIMITING OUTFLOW ALONG THE WESTERN PERIPHERY. THE STORM IS
BEING STEERED BY A DEEP-LAYERED SUBTROPICAL RIDGE TO THE EAST.
3. FORECAST REASONING.
A. THERE IS NO SIGNIFICANT CHANGE TO THE FORECAST PHILOSPHY.
B. TS 16W IS FORECAST TO INITIALLY WEAKEN AS CONVECTION ERODES
DUE TO ITS ABNORMALLY FAST STORM MOTION AND INCREASING VERTICAL
WIND SHEAR AHEAD OF AN APPROACHING MID-LATITUDE TROUGH FROM THE
NORTHWEST. THIS TROUGH WILL WEAKEN THE STEERING RIDGE AND CAUSE
THE CYCLONE TO MOMENTARILY RECURVE SLIGHTLY EAST OF TRACK. AFTER
TAU 36, THE SYSTEM IS EXPECTED TO TURN MORE POLEWARD AS A HIGH
AMPLITUDE SUBTROPICAL RIDGE TO THE EAST OF NORTHERN JAPAN WILL
BUILD AND ASSUME STEERING. THE INITIAL EXPOSURE TO STRONG WESTERLIES
WILL ENHANCE OUTFLOW AND SLIGHTLY INTENSIFY THE STORM, ALBEIT FOR A
SHORT PERIOD. AFTER TAU 48, THE SYSTEM WILL BEGIN EXTRA-TROPICAL
TRANSITION (ET) AND WEAKEN AS VWS INCREASES AND SEA SURFACE
TEMPERATURES COOL. THE SYSTEM WILL COMPLETE ET BY END OF FORECAST.
GIVEN THE EXCEEDINGLY FAST STORM MOTION, THERE IS A DISTINCT
POSSIBILITY THAT THE SYSTEM WILL DISSIPATE BEFORE TAU 36. THE
NUMERICAL MODEL GUIDANCE IS IN FAIR AGREEMENT UP TO TAU 48 BEFORE
IT FANS OUT TO APPROXIMATELY 30 DEGREES WITH EGRR TO THE LEFT OF
AND JGSM AND WBAR TO THE RIGHT OF THE ENVELOPE. THIS TRACK FORECAST
IS TO THE RIGHT OF CONSENSUS. NEXT WARNINGS AT 040900Z, 041500Z,
042100Z AND 050300Z. REFER TO TROPICAL DEPRESSION 15W (TALAS)
WARNINGS (WTPN32 PGTW) FOR SIX-HOURLY UPDATES.//

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