WTNT41 KNHC 122057
TCDAT1
 
TROPICAL DEPRESSION SIX DISCUSSION NUMBER   1
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL062011
500 PM EDT FRI AUG 12 2011
 
THE LOW PRESSURE SYSTEM THAT HAS BEEN EMBEDDED WITHIN A BAROCLINIC
ZONE OFF THE SOUTHEAST UNITED STATES COAST DURING THE PAST DAY OR
TWO HAS LOST ITS FRONTAL CHARACTERISTICS OVER THE WARM ATLANTIC
WATERS. IN ADDITION...DEEP CONVECTION HAS BEEN INCREASING OVER THE
WELL-DEFINED LOW-LEVEL CENTER DURING THE PAST SEVERAL HOURS. BASED
ON ITS PRESENTATION IN SATELLITE IMAGERY AND EARLIER BUOY
REPORTS...THIS SYSTEM IS BEING DESIGNATED AS A TROPICAL DEPRESSION
WITH AN INITIAL INTENSITY OF 30 KT. SIGNIFICANT STRENGTHENING IS
NOT FORECAST SINCE THE DEPRESSION SHOULD REMAIN WITHIN AN
ENVIRONMENT OF INCREASING SOUTHWESTERLY SHEAR...FAIRLY DRY
MID-LEVEL AIR...AND PROGRESSIVELY COOLER WATERS. THE OFFICIAL
INTENSITY FORECAST IS CLOSE TO THE LGEM. EXTRATROPICAL TRANSITION
IS EXPECTED TO OCCUR IN ABOUT 36-48 HOURS ONCE THE CYCLONE MOVES
OVER WATERS COOLER THAN 25C AND INTERACTS WITH AN APPROACHING
FRONTAL BOUNDARY.

THE DEPRESSION IS MOVING 065/14 AND IS EMBEDDED WITHIN DEEP-LAYER
SOUTHWESTERLY FLOW BETWEEN A RIDGE OVER THE CENTRAL ATLANTIC OCEAN
AND A TROUGH OFFSHORE OF THE U.S. EAST COAST. THIS FLOW PATTERN IS
NOT EXPECTED TO CHANGE MUCH OVER THE NEXT COUPLE OF DAYS AND THAT
SHOULD KEEP THE CYCLONE MOVING IN THE SAME GENERAL HEADING UNTIL IT
MERGES WITH A FRONT. THE OFFICIAL TRACK FORECAST IS A LITTLE FASTER
THAN THE MODEL CONSENSUS...AND CLOSE TO A BLEND OF THE GFS AND
ECMWF MODELS.
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  12/2100Z 36.0N  63.9W   30 KT  35 MPH
 12H  13/0600Z 37.0N  61.4W   35 KT  40 MPH
 24H  13/1800Z 38.5N  57.8W   40 KT  45 MPH
 36H  14/0600Z 39.8N  53.9W   40 KT  45 MPH
 48H  14/1800Z 40.6N  49.8W   40 KT  45 MPH...POST-TROP/EXTRATROP
 72H  15/1800Z...DISSIPATED
 
$$
FORECASTER CANGIALOSI/STEWART
 

WTNT41 KNHC 130236
TCDAT1
 
TROPICAL DEPRESSION SIX DISCUSSION NUMBER   2
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL062011
1100 PM EDT FRI AUG 12 2011

THROUGH 0000 UTC...THE DEPRESSION WAS MAINTAINING A CENTRAL DENSE
OVERCAST...WITH SSM/IS AND TRMM DATA NEAR 2330 UTC SHOWING SOME
CONVECTIVE CURVATURE NEAR THE CENTER.  SINCE THEN...THE CONVECTION
HAS DIMINISHED...ALTHOUGH IT IS UNCLEAR WHETHER THIS IS A DIURNAL
MINIMUM OR THE START OF A WEAKENING TREND.  SATELLITE INTENSITY
ESTIMATES FROM TAFB AND SAB ARE 30 KT...AND THAT REMAINS THE
INITIAL INTENSITY.

THE INITIAL MOTION IS 065/19.  THE DEPRESSION IS MOVING ALONG THE
SOUTHEASTERN EDGE OF THE WESTERLIES AND TO THE NORTHWEST OF THE
SUBTROPICAL RIDGE.  ALL GUIDANCE AGREES THAT THE SYSTEM SHOULD MOVE
GENERALLY EAST-NORTHEASTWARD FOR 24 HR OR SO...FOLLOWED BY A MOTION
TOWARD THE EAST THAT SHOULD CONTINUE UNTIL DISSIPATION.  THE NEW
FORECAST TRACK IS A LITTLE SOUTH OF THE PREVIOUS TRACK BASED ON THE
INITIAL POSITION AND MOTION...AND IT LIES NEAR THE CENTER OF THE
TRACK GUIDANCE ENVELOPE.

THE DEPRESSION IS JUST SOUTHEAST OF A FRONTAL SYSTEM AND IS MOVING
TOWARD COOLER WATERS.  IN ADDITION...VERTICAL WIND SHEAR IS FORECAST
TO INCREASE AFTER 6-12 HOURS.  THEREFORE...THERE IS ONLY A SHORT
WINDOW FOR INTENSIFICATION.  THE INTENSITY FORECAST CALLS FOR
MODEST STRENGTHENING DURING THE NEXT 12 HOURS...FOLLOWED BY
EXTRATROPICAL TRANSITION AS THE DEPRESSION MERGES WITH THE FRONTAL
SYSTEM.  THE CYCLONE IS FORECAST TO DISSIPATE COMPLETELY WITHIN THE
FRONTAL ZONE BY 72 HR...AND THIS COULD EVEN OCCUR EARLIER.  THE
INTENSITY FORECAST IS A LITTLE LESS INTENSE THAN THE FORECAST OF
THE SHIPS AND LGEM MODELS.

 
FORECAST POSITIONS AND MAX WINDS
 
INIT  13/0300Z 36.6N  61.3W   30 KT  35 MPH
 12H  13/1200Z 37.8N  58.4W   35 KT  40 MPH
 24H  14/0000Z 39.3N  54.2W   35 KT  40 MPH
 36H  14/1200Z 40.3N  50.0W   35 KT  40 MPH...POST-TROP/EXTRATROP
 48H  15/0000Z 40.3N  45.6W   35 KT  40 MPH...POST-TROP/EXTRATROP
 72H  16/0000Z...DISSIPATED
 
$$
FORECASTER BEVEN
 

