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Subtropical Depression SEVENTEEN


ZCZC MIATCDAT2 ALL
TTAA00 KNHC DDHHMM
SUBTROPICAL DEPRESSION SEVENTEEN DISCUSSION NUMBER   2
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   AL172010
1100 AM AST WED OCT 06 2010
 
DURING THE PAST 6 HOURS...SATELLITE IMAGERY INDICATES THAT DEEP
CONVECTION HAS DEVELOPED IN THE NORTHWEST QUADRANT CLOSER TO THE
CENTER. HOWEVER...VISIBLE IMAGERY ALSO INDICATES THAT THERE ARE
MULTIPLE SMALL SWIRLS ROTATING AROUND THE CENTER OF THE LARGER
CYCLONIC GYRE. AS A RESULT...THE INITIAL POSITION IS LOCATED AT THE
MEAN CENTER OF THE BROADER CIRCULATION. SATELLITE INTENSITY
ESTIMATES ARE A CONSENSUS TROPICAL T2.5/35 KT FROM TAFB AND
SAB...AND AN ADT ESTIMATE OF T2.1/31 KT FROM UW-CIMSS. EARLIER AMSU
TEMPERATURE DATA ALSO INDICATED THAT A WEAK WARM CORE WAS LOCATED
BETWEEN 600-400 MB...SUGGESTING THAT THE SYSTEM WAS NOT FULLY NOT
FULLY TROPICAL. GIVEN THAT THIS SYSTEM IS STILL INTERACTING WITH AN
UPPER-LEVEL LOW NOTED IN WATER VAPOR IMAGERY TO BE CENTERED JUST
SOUTHEAST OF THE LOW-LEVEL CENTER...THE INITIAL INTENSITY WILL BE
HELD AT 30 KT AND THE SYSTEM WILL ALSO RETAIN SUBTROPICAL
DEPRESSION STATUS FOR THIS ADVISORY. AN AIR FORCE RESERVE
RECONNAISSANCE AIRCRAFT IS SCHEDULED TO INVESTIGATE THE CYCLONE
AROUND 18Z...WHICH SHOULD PROVIDE A BETTER INTENSITY ESTIMATE.
 
THE INITIAL MOTION ESTIMATE IS 325/8 BASED ON MICROWAVE POSITIONS
AND USING THE AFOREMENTIONED MEAN FIX POSITION DATA. THE CYCLONE IS
MOVING NORTHWESTWARD TOWARD A WEAKNESS IN A DEEP-LAYER RIDGE LOCATED
TO THE NORTH. A WEAK COLD FRONTAL SYSTEM IS EMBEDDED IN THE
WEAKNESS...AND A STRONG MID-TROPOSPHERIC TROUGH LOCATED OVER THE
EASTERN U.S. IS FORECAST TO MOVE EASTWARD AND WEAKEN THE RIDGE AND
ALSO STRENGTHEN THE FRONT SYSTEM. THE CYCLONE IS EXPECTED TO
GRADUALLY MOVE THROUGH THE WEAKNESS AND ACCELERATE AHEAD OF THE
TROUGH AFTER 36 HOURS...AND MERGE WITH THE FRONTAL SYSTEM AND
BECOME EXTRATROPICAL BY 96 HOURS. THE FORECAST IS A LITTLE TO THE
LEFT OF THE PREVIOUS TRACK...MAINLY DUE TO THE MORE WESTWARD
INITIAL POSITION...AND IS SIMILAR TO THE CONSENSUS MODEL...TVCN.
 
GRADUAL TRANSITION TO A FULLY TROPICAL LOW PRESSURE SYSTEM IS
EXPECTED TO OCCUR WITHIN THE NEXT 12 HOURS NOW THAT DEEP CONVECTION
HAS DEVELOPED WITHIN ABOUT 30 NMI OF THE LOW-LEVEL CENTER.
HOWEVER...THIS TROPICAL TRANSITION COULD COMPLICATE THE INTENSITY
FORECAST SINCE TROPICAL CYCLONE INTENSIFICATION PROCESSES USUALLY
OCCUR ON MUCH SHORTER TIME SCALES THAN THOSE ASSOCIATED WITH
SUBTROPICAL CYCLONES. THE VERTICAL SHEAR IS FORECAST TO REMAIN
RELATIVELY LOW FOR THE NEXT 36-48 HOURS WHILE THE CYCLONE WILL BE
OVER WARM SSTS OF GREATER THAN 28C. THIS SHOULD ALLOW FOR AT LEAST
SOME MODEST STRENGTHENING TO OCCUR. THE OFFICIAL INTENSITY FORECAST
IS A BLEND OF ALL OF THE NHC INTENSITY GUIDANCE. HOWEVER...IT
SHOULD BE NOTED THAT THE SHIPS MODEL MAKES THE CYCLONE A HURRICANE
BY 72 HOURS...WHICH IS A VIABLE POSSIBILITY IF THE SYSTEM TAKES ON
A MORE CLASSICAL TROPICAL CYCLONE STRUCTURE.
 

FORECAST POSITIONS AND MAX WINDS
 
INITIAL      06/1500Z 23.0N  68.0W    30 KT
 12HR VT     07/0000Z 23.5N  68.3W    35 KT
 24HR VT     07/1200Z 24.2N  68.2W    40 KT
 36HR VT     08/0000Z 24.9N  67.2W    45 KT
 48HR VT     08/1200Z 26.1N  65.2W    50 KT
 72HR VT     09/1200Z 29.3N  58.3W    50 KT
 96HR VT     10/1200Z 33.4N  47.4W    40 KT...POST-TROP/EXTRATROP
120HR VT     11/1200Z 38.0N  34.5W    35 KT...POST-TROP/EXTRATROP
 
$$
FORECASTER STEWART
 
NNNN


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Page last modified: Friday, 15-Apr-2011 12:09:20 UTC