Textbook dual outflow channels
Posted by JAC on 9/12/2009, 9:40 pm



REMARKS:
122100Z POSITION NEAR 15.7N 150.2E.
TROPICAL STORM (TS) 15W (CHOI-WAN), LOCATED APPROXIMATELY 260 NM
EAST OF SAIPAN, HAS TRACKED WEST-NORTHWESTWARD AT 13 KNOTS OVER THE
PAST SIX HOURS. ANIMATED INFRARED IMAGERY SHOWS MULTIPLE SPIRAL
BANDS WRAPPING INTO DEEP, CENTRAL CONVECTION. THE IMAGERY AND UPPER-
LEVEL ANALYSIS DEPICT GREAT RADIAL OUTFLOW. ADDITIONALLY, A POLEWARD
OUTFLOW CHANNEL INTO A DEEPENING TROPICAL UPPER TROPOSPHERIC TROUGH
(TUTT) CELL TO THE EAST IS QUICKLY DEVELOPING. THE MODEL AIDS ARE IN
VERY GOOD AGREEMENT WITH THIS FORECAST AS THEY HAVE ALL STARTED TO
SHIFT SLIGHTLY TO THE NORTH OF SAIPAN. HOWEVER, THE 12Z UPPER-LEVEL
SOUNDING AT MINAMITORISHIMA (RJAM, 24.5N 154.0E) REPORTS EASTERLY
WINDS THROUGHOUT THE COLUMN, INDICATING THAT THE SUBTROPICAL RIDGE
IS STILL FIRMLY IN PLACE. THEREFORE, THIS FORECAST TAKES THE SYSTEM
WESTWARD THROUGH TAU 36 BEFORE THE MID-LATITUDE TROUGH CURRENTLY
OVER JAPAN SLIGHTLY WEAKENS THE SUBTROPICAL RIDGE, ALLOWING FOR A
MORE NORTHWESTWARD TRACK THROUGH TAU 120. THE UPGRADE IN INTENSITY
TO TROPICAL STORM STRENGTH AS WELL AS THE CURRENT POSITION ARE BASED
ON THE 121730Z PGTW FIX AND ARE SUPPORTED BY A WELL-DEVELOPED LOW
LEVEL SIGNATURE DEPICTED IN THE 121531Z AMSRE MICROWAVE IMAGE. MAX-
IMUM SIGNIFICANT WAVE HEIGHT AT 121800Z IS 12 FEET. NEXT WARNINGS AT
130300Z, 130900Z, 131500Z AND 132100Z.//
NNNN
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WP15 Choi-Wan should ramp up to a super typhoon this week - JAC, 9/12/2009, 9:36 pm
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