Subject: Pacific-NW: Subj/prognostic Reasoning For Tropical Depression 12w Warning Nr 02//

From: SIU Weather Processor <[email-masked]>
Date: Tue, 14 Sep 2010 21:45:05 -0500

WDPN31 PGTW 150300
MSGID/GENADMIN/NAVMARFCSTCEN PEARL HARBOR HI/JTWC//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 12W WARNING NR 02//
RMKS/
1. FOR METEOROLOGISTS.
2. 12 HOUR SUMMARY AND ANALYSIS.
   A. TROPICAL DEPRESSION (TD) 12W (TWELVE), LOCATED APPROXIMATELY
380 NM SOUTH OF OKINAWA, JAPAN HAS TRACKED NORTHWESTWARD AT 09 KNOTS
OVER THE PAST SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE IMAGERY
SHOWS CONVECTIVE BANDING WRAPPING INTO A LOW LEVEL CIRCULATION
CENTER (LLCC) WITH THE MAJORITY OF DEEP CONVECTION IN THE
SOUTHEASTERN QUADRANT AND NORTHERN PERIPHERY. THE INITIAL POSITION
IS BASED ON A 142138Z CORIOLIS MICROWAVE IMAGE THAT SHOWS CURVED LOW
LEVEL CONVECTIVE BANDING. THE INITIAL INTENSITY IS BASED ON THE PGTW
DVORAK ESTIMATE OF 30 KNOTS AND DROPSONDE OBSERVATIONS OF 27 TO 30
KNOTS AT 142157Z AND 142209Z RESPECTIVELY. A TROPICAL UPPER
TROPOSPHERIC TROUGH (TUTT) TO THE WEST AND NORTH IS CAUSING
SUBSIDENCE AND LIMITING POLEWARD OUTFLOW. HOWEVER, THERE IS MODERATE
EQUATORWARD OUTFLOW. TD 12W IS LOCATED IN AN AREA OF LOW VERTICAL
WIND SHEAR AND GOOD DIVERGENCE ALOFT FAVORABLE FOR DEVELOPMENT.
3. FORECAST REASONING.
   A. THIS IS THE FIRST ISSUANCE OF THE PROGNOSTIC REASONING MESSAGE.
   B. TD 12W IS CURRENTLY TRACKING ALONG THE SOUTHWESTERN PERIPHERY
OF A LOW- TO MID-LEVEL STEERING RIDGE IN A WEAK STEERING
ENVIRONMENT. AROUND TAU 36, TD 12W IS EXPECTED TO CONTINUE SLOWLY
TRACKING NORTHWESTWARD AND TURN NORTHWARD AS AN UPPER LEVEL, MID-
LATITUDE TROUGH WEAKENS THE STEERING RIDGE TO THE NORTH. TD 12W IS
THEN FORECAST TO TURN NORTHEASTWARD, SOUTH OF OKINAWA, AND BEGIN
TRACKING ALONG THE NORTHWESTERN PERIPHERY OF A STEERING RIDGE
EXTENSION THAT BUILDS IN TO THE SOUTH. AS TD 12W CONTINUES TO TRACK
FARTHER NORTH, POLEWARD OUTFLOW SHOULD INCREASE INTO THE MID-
LATITUDE UPPER LEVEL TROUGH AND INTO THE TUTT CELL TO THE EAST,
WHICH WILL ALLOW FOR INTENSIFICATION.
   C. BY TAU 96, TD 12W IS EXPECTED TO TURN NORTHWESTWARD AS THE
SUBTROPICAL RIDGE TO THE NORTH BUILDS BACK IN. THE SYSTEM IS
FORECAST TO CONTINUE INTENSIFYING THROUGHOUT THE FORECAST PERIOD AND
REACH TYPHOON STRENGTH BY TAU 96. THE NUMERICAL MODEL GUIDANCE IS IN
AGREEMENT IN TRACK PHILOSOPHY, ALTHOUGH DIFFERS IN THE TIMING OF
BOTH TURNS TO THE NORTHEAST AND TO THE NORTHWEST. THIS FORECAST IS
IN AGREEMENT WITH THE NOGAPS, GFS, AND JGSM MODELS, WHICH TURN THE
SYSTEM MORE SLOWLY AND TRACKS THE SYSTEM SOUTH OF OKINAWA. HOWEVER,
GFDN PULLS TD 12W FASTER NORTHWARD AND THEN NORTHWESTWARD OVER
OKINAWA AS IT ANALYSES THE RIDGE TO WEAKEN AND THEN BUILD BACK IN
FASTER THAN THE OTHER MODELS. THIS IS ALSO A POSSIBLE SCENARIO.//

+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
To unsubscribe from WX-TROPL send e-mail to [email-masked] with
"unsub wx-tropl" in the body of your message. For help with WX-TROPL
write to [email-masked]. For more information on tropical weather products, see the NHC Homepage at http://www.nhc.noaa.gov.