Post by nolasim on Oct 4, 2013 3:01:57 GMT -6
NHC has once again moved its track to the left. It does not mention anything close to dissipation in its discussion. Definitely continues to bear careful monitoring for potential impacts to SE LA.
TROPICAL STORM KAREN DISCUSSION NUMBER 5
NWS NATIONAL HURRICANE CENTER MIAMI FL AL122013
400 AM CDT FRI OCT 04 2013
KAREN IS SHOWING THE AFFECTS OF 20-25 KT OF WESTERLY VERTICAL WIND
SHEAR. THE MAIN CONVECTIVE AREA IS NOW LOCATED ABOUT 100 N MI EAST
OF THE CENTER...WITH ONLY OCCASIONAL SHOWERS AND THUNDERSTORM
ACTIVITY NEAR THE CENTER. REPORTS FROM AIR FORCE RESERVE AND NOAA
HURRICANE HUNTER AIRCRAFT INDICATE THAT THE CENTRAL PRESSURE HAS
RISEN TO 1002 MB...AND THAT BOTH THE FLIGHT-LEVEL AND SFMR WINDS
HAVE DECREASED. BASED ON THE AIRCRAFT DATA...THE INITIAL INTENSITY
IS REDUCED TO A POSSIBLY GENEROUS 50 KT.
THE INITIAL MOTION IS 325/9. KAREN IS CURRENTLY BEING STEERED BY A
LOW/MID-LEVEL RIDGE OVER THE SOUTHEASTERN UNITED STATES. THIS
RIDGE IS FORECAST TO WEAKEN AS A LARGE DEEP-LAYER TROUGH MOVES
EASTWARD INTO THE CENTRAL UNITED STATES. THIS EVOLUTION SHOULD
CAUSE KAREN TO TURN NORTHWARD AND EVENTUALLY NORTHEASTWARD...WITH
THE BIG QUESTION BEING THE TIMING OF THE NORTHEASTWARD TURN. THE
UKMET...NAVGEM...AND CANADIAN MODELS DELAY THE TURN UNTIL AFTER
KAREN MAKES LANDFALL IN SOUTHERN LOUISIANA. THE GFS SHOWS THE
SHARPEST TURN...AND IT CALLS FOR THE CENTER TO MAKE LANDFALL ON THE
NORTHWESTERN FLORIDA PENINSULA. THE GFDL...HWRF...AND ECMWF ARE
BETWEEN THESE EXTREMES WITH LANDFALL FORECASTS FROM THE MOUTH OF
THE MISSISSIPPI RIVER TO THE WESTERN FLORIDA PANHANDLE. OVERALL...
THE GUIDANCE IS SLOWER THAN IT WAS 6 HOURS AGO...AND THE GUIDANCE
ENVELOPE HAS SHIFTED A LITTLE TO THE WEST DURING THE FIRST 48
HOURS. THE NEW FORECAST TRACK REFLECTS THESE TRENDS WITH A SLIGHT
WESTWARD SHIFT AND A SLOWER FORWARD SPEED. GIVEN THE SPREAD OF
THE GUIDANCE...THE FORECAST OF THE LANDFALL POSITION IS LOW
CONFIDENCE.
THE INTENSITY FORECAST IS RATHER PROBLEMATIC. FIRST...KAREN IS
LIKELY TO INTERACT WITH A SMALL UPPER-LEVEL TROUGH DURING THE NEXT
24 HOURS...WHICH MIGHT PROVIDE SOME SUPPORT FOR RENEWED CONVECTION.
SECOND...THE SHEAR MAY DIMINISH IN THE WAKE OF THE TROUGH...WHICH
COULD ALLOW FOR INTENSIFICATION...ESPECIALLY IF KAREN TURNS
NORTHEASTWARD WHILE STILL OVER WATER. THE ECMWF SHOWS ABOUT 10 MB
OF DEEPENING AFTER RECURVATURE...AND THE GFS...HWRF...AND GFDL
MODELS SHOW MORE. BASED ON THESE MODELS AND CURRENT TRENDS...THE
INTENSITY FORECAST IS MODIFIED TO SHOW LITTLE CHANGE IN STRENGTH
THROUGH 24 HOURS...FOLLOWED BY INTENSIFICATION TO NEAR HURRICANE
STRENGTH BY 48 HOURS. AFTER LANDFALL...KAREN SHOULD WEAKEN AND
EVENTUALLY BECOME EXTRATROPICAL AS IT MERGES WITH THE DEEP-LAYER
TROUGH.
SINCE THE CURRENT FORECAST IS SLOWER THAN THE PREVIOUS FORECAST...NO
CHANGE IN WATCHES AND WARNINGS IS NECESSARY AT THIS TIME. THIS
WILL BE REVISITED AS KAREN PROGRESSES NORTHWARD ACROSS THE CENTRAL
GULF OF MEXICO.
FORECAST POSITIONS AND MAX WINDS
INIT 04/0900Z 24.9N 89.8W 50 KT 60 MPH
12H 04/1800Z 25.9N 90.1W 50 KT 60 MPH
24H 05/0600Z 27.0N 90.4W 50 KT 60 MPH
36H 05/1800Z 28.0N 90.4W 55 KT 65 MPH
48H 06/0600Z 29.1N 89.5W 60 KT 70 MPH
72H 07/0600Z 32.5N 84.5W 35 KT 40 MPH...INLAND
96H 08/0600Z 37.5N 77.5W 25 KT 30 MPH...POST-TROP/EXTRATROP
120H 09/0600Z...DISSIPATED
