WTNT43 KNHC 032100
TCDAT3
 
TROPICAL DEPRESSION THIRTEEN DISCUSSION NUMBER   1
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL132012
500 PM EDT MON SEP 03 2012
 
THE SMALL LOW PRESSURE SYSTEM LOCATED OVER THE CENTRAL
ATLANTIC...WHICH DEVELOPED FROM AN UPPER-LEVEL TROUGH...HAS
GRADUALLY ACQUIRED ENOUGH ORGANIZED DEEP CONVECTION TO BE
CLASSIFIED AS A TROPICAL DEPRESSION. VISIBLE SATELLITE IMAGERY AND
AN EARLIER ASCAT PASS INDICATED THAT THE LOW HAS A WELL-DEFINED
CENTER AND RELIABLE WINDS OF AROUND 25 KT. THE INITIAL INTENSITY IS
SET A LITTLE HIGHER AT 30 KT SINCE ASCAT HAS A KNOWN LOW BIAS AND
BECAUSE THE RESOLUTION OF THE INSTRUMENT LIKELY CAN NOT RESOLVE THE
SMALL RADIUS OF MAXIMUM WINDS.
 
THE DEPRESSION CURRENTLY LIES BENEATH A TROUGH AXIS...WHERE THE
UPPER-LEVEL WINDS APPEAR RELATIVELY LIGHT. GLOBAL MODELS SHOW THE
TROUGH AND THE CYCLONE MOVING IN TANDEM...WHICH KEEPS THE
DEPRESSION IN A MARGINALLY FAVORABLE UPPER-LEVEL WIND PATTERN FOR A
DAY OR SO. THEREFORE...SOME SLIGHT STRENGTHENING IS SHOWN IN THE
SHORT TERM. BY LATE WEDNESDAY...THE TROUGH IS EXPECTED TO LIFT OUT
AND WEAKEN. THIS WILL CAUSE AN INCREASE IN NORTHWESTERLY
SHEAR...AND WILL LIKELY RESULT IN WEAKENING. THE SYSTEM IS 
EXPECTED TO DEGENERATE TO A REMNANT LOW IN A FEW DAYS.

THE DEPRESSION IS FORECAST TO MOVE SLOWLY WEST-NORTHWESTWARD AROUND
THE SOUTHWESTERN PORTION OF A RIDGE OVER THE EASTERN ATLANTIC
DURING THE NEXT 24 HOURS.  AFTER THAT TIME...THE CYCLONE IS
EXPECTED TO TURN NORTHWARD AS THE WESTERN PORTION OF THE RIDGE
ERODES.  
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  03/2100Z 25.6N  42.2W   30 KT  35 MPH
 12H  04/0600Z 25.8N  42.9W   35 KT  40 MPH
 24H  04/1800Z 26.4N  43.7W   35 KT  40 MPH
 36H  05/0600Z 27.3N  44.3W   35 KT  40 MPH
 48H  05/1800Z 28.0N  44.5W   30 KT  35 MPH
 72H  06/1800Z 28.5N  44.5W   25 KT  30 MPH...POST-TROP/REMNT LOW
 96H  07/1800Z 29.5N  44.5W   20 KT  25 MPH...POST-TROP/REMNT LOW
120H  08/1800Z 30.5N  44.5W   20 KT  25 MPH...POST-TROP/REMNT LOW
 
$$
FORECASTER BROWN/CANGIALOSI
 

WTNT43 KNHC 040300
TCDAT3
 
TROPICAL DEPRESSION THIRTEEN DISCUSSION NUMBER   2
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL132012
1100 PM EDT MON SEP 03 2012
 
THE CLOUD PATTERN OF THE DEPRESSION HAS NOT CHANGED MUCH IN
ORGANIZATION THIS EVENING. THE CENTER OF THE SYSTEM APPEARS TO
BE NEAR OR JUST UNDER THE WESTERN EDGE OF A RATHER LINEAR BAND OF
SHALLOW CONVECTION...SUGGESTIVE OF NORTHWESTERLY SHEAR. DVORAK
T-NUMBERS ARE AT 2.0 FROM TAFB AND SAB...SO THE INITIAL INTENSITY
ESTIMATE IS HELD AT 30 KT.  THE DEPRESSION IS OVER WARM WATERS AND
REMAINS EMBEDDED IN AN UPPER-LEVEL TROUGH WHERE THE SHEAR IS
RELATIVELY LOW.  AS THIS FEATURE LIFTS OUT DURING THE NEXT DAY OR
SO...STRONG NORTHWESTERLY FLOW ASSOCIATED WITH AN INTENSE SHORTWAVE
TROUGH SOUTHEAST OF THE CANADIAN MARITIME PROVINCES IS FORECAST TO
IMPINGE ON THE DEPRESSION.  THIS IS EVIDENCED BY CROSS-SECTION
ANALYSES OF THE ECMWF/GFS MODELS WHICH SHOW A CONSIDERABLE
SOUTHEASTWARD TILT OF THE VORTEX WITH HEIGHT.  THE ABRUPT INCREASE
IN SHEAR SHOULD BE SUBSTANTIAL ENOUGH TO CAUSE WEAKENING...
ESPECIALLY FOR A SMALL SYSTEM SUCH AS THIS ONE.  THE NHC INTENSITY
FORECAST IS UNCHANGED FROM THE PREVIOUS ONE...CONSERVATIVELY
SHOWING REMNANT LOW STATUS IN 3 DAYS.
 
SATELLITE DATA SUGGEST AN INITIAL MOTION ESTIMATE OF 305/04.  THE
DEPRESSION IS MOVING SLOWLY NORTHWESTWARD AROUND THE WESTERN
PERIPHERY OF A SUBTROPICAL RIDGE TO THE EAST...AND SHOULD TURN
NORTH-NORTHWESTWARD AND NORTHWARD DURING THE NEXT DAY OR TWO AS A
SHORTWAVE PASSES TO THE NORTH AND ERODES THE RIDGE FURTHER. THE
OFFICIAL TRACK FORECAST IS NEAR THE PREVIOUS ONE THROUGH 48 HOURS
AND IS ADJUSTED TO THE RIGHT AFTER THAT...IN GOOD AGREEMENT WITH
THE LATEST HWRF MODEL.
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  04/0300Z 25.9N  42.8W   30 KT  35 MPH
 12H  04/1200Z 26.3N  43.3W   35 KT  40 MPH
 24H  05/0000Z 27.0N  44.1W   35 KT  40 MPH
 36H  05/1200Z 27.8N  44.5W   30 KT  35 MPH
 48H  06/0000Z 28.5N  44.3W   25 KT  30 MPH
 72H  07/0000Z 29.5N  44.0W   20 KT  25 MPH...POST-TROP/REMNT LOW
 96H  08/0000Z 31.0N  44.0W   15 KT  15 MPH...POST-TROP/REMNT LOW
120H  09/0000Z...DISSIPATED
 
$$
FORECASTER KIMBERLAIN
 

WTNT43 KNHC 040842
TCDAT3
 
TROPICAL DEPRESSION THIRTEEN DISCUSSION NUMBER   3
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL132012
500 AM EDT TUE SEP 04 2012
 
SMALL BANDS OF DEEP CONVECTION CONTINUE TO WRAP AROUND THE EASTERN
SIDE OF THE DEPRESSION AND NIGHT VISIBLE IMAGES INDICATE THE CENTER
IS JUST WEST OF THE SOUTHERNMOST BAND. INTENSITY ESTIMATES WERE 35
KT AND 30 KT FROM TAFB/SAB RESPECTIVELY...AND GIVEN THE LACK OF ANY
SIGNIFICANT CHANGE IN SATELLITE IMAGERY DURING THE PAST FEW
HOURS...THE INITIAL WINDS ARE KEPT AT 30 KT. 

THE FUTURE STRENGTH OF THE DEPRESSION IS NOT AN EASY PREDICTION AS
IT IS VERY CLOSE TO SOME STRONG NORTHWESTERLY SHEAR. HOWEVER...THE
BULK OF THE MODEL GUIDANCE IS NOW INDICATING THAT THIS SHEAR WILL
STAY AWAY FROM THE CYCLONE...WITH LITTLE CHANGE IN THE ENVIRONMENT
PROBABLE FOR THE NEXT COUPLE OF DAYS WHILE THE CYCLONE REMAINS OVER
WARM WATERS. AN UPPER-LEVEL TROUGH IS FORECAST BY MANY GLOBAL
MODELS TO CUT OFF TO THE SOUTHWEST OF THE DEPRESSION IN A FEW
DAYS...WHICH COULD CREATE A FAVORABLE WIND PATTERN FOR
INTENSIFICATION. WITH THE CHANGE IN THE FORECAST LARGE-SCALE
ENVIRONMENT...IT DOES NOT SEEM AS LIKELY THAT THE DEPRESSION WILL
BECOME A REMNANT LOW ANYTIME SOON...AND THE NEW FORECAST NO LONGER
SHOWS THAT TRANSITION. THE LATEST PREDICTION IS CLOSE TO THE MODEL
CONSENSUS DURING THE FORECAST PERIOD...BUT IS MUCH LOWER THAN THE
SHIPS/LGEM GUIDANCE. IF THE DEPRESSION WERE TO TRACK FARTHER TO THE
LEFT THAN ANTICIPATED IN THE NEAR TERM...THEN MORE WEAKENING THAN
SHOWN BELOW IS LIKELY...WHICH COULD ALSO CAUSE THE SYSTEM TO
DEGENERATE INTO A REMNANT LOW.
 
BEST ESTIMATE OF INITIAL MOTION IS 310/5. THE CYCLONE SHOULD TURN
TOWARD THE NORTH-NORTHWEST AND NORTH OVER THE NEXT 24H OR SO AS IT
MOVES AROUND A WEAK SUBTROPICAL RIDGE OVER THE EASTERN ATLANTIC
OCEAN. STEERING CURRENTS ARE QUITE LIGHT AFTER THAT TIME...WITH THE
MIDDLE- TO UPPER-LEVEL LOW DROPPING TO THE SOUTH AND WEST OF THE
DEPRESSION IN A FEW DAYS THAT COULD CAUSE A SLOW NORTHWEST OR
NORTHWARD MOTION IN THE 3 TO 5 DAY PERIOD. THE LATEST NHC FORECAST
IS VERY CLOSE TO THE PREVIOUS ONE...BUT IS ADJUSTED A BIT TO THE
NORTH AND WEST AT LONG RANGE...ON THE LEFT SIDE OF THE TVCA MODEL.

FORECAST POSITIONS AND MAX WINDS
 
INIT  04/0900Z 26.5N  43.3W   30 KT  35 MPH
 12H  04/1800Z 26.9N  43.9W   30 KT  35 MPH
 24H  05/0600Z 27.6N  44.3W   30 KT  35 MPH
 36H  05/1800Z 28.3N  44.4W   30 KT  35 MPH
 48H  06/0600Z 28.8N  44.0W   30 KT  35 MPH
 72H  07/0600Z 30.0N  43.5W   30 KT  35 MPH
 96H  08/0600Z 31.5N  44.5W   35 KT  40 MPH
120H  09/0600Z 33.0N  44.5W   35 KT  40 MPH
 
$$
FORECASTER BLAKE
 

