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Tropical Storm KAREN Forecast Discussion Number 5

2013-10-04 10:52:17| National Hurricane Center (Atlantic)

Issued at 400 AM CDT FRI OCT 04 2013 000 WTNT42 KNHC 040851 TCDAT2 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 $$ FORECASTER BEVEN

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Tropical Storm KAREN Forecast Discussion Number 4

2013-10-04 04:44:35| National Hurricane Center (Atlantic)

Issued at 1000 PM CDT THU OCT 03 2013 000 WTNT42 KNHC 040244 TCDAT2 TROPICAL STORM KAREN DISCUSSION NUMBER 4 NWS NATIONAL HURRICANE CENTER MIAMI FL AL122013 1000 PM CDT THU OCT 03 2013 KAREN CONTINUES TO BE A SHEARED CYCLONE WITH A VIGOROUS CIRCULATION...AND WITH MOST OF THE THUNDERSTORM ACTIVITY TO THE NORTH AND EAST OF THE CENTER. THERE HAS BEEN AN EXCELLENT COVERAGE BY BOTH AIR FORCE AND NOAA HURRICANE HUNTER PLANES DURING THE PAST SEVERAL HOURS. BASED ON THAT RECONNAISSANCE DATA...THE INITIAL INTENSITY IS KEPT AT 55 KNOTS IN THIS ADVISORY. THE SHEAR AFFECTING KAREN IS FORECAST TO INCREASE AND THIS WOULD SUGGEST WEAKENING. IT IS BECOMING LESS REALISTIC THAT KAREN WILL BECOME A HURRICANE IN A DAY OR TWO...BUT GIVING CREDIT TO SOME DYNAMICAL MODELS...LIKE THE HWRF...WHICH DO SO...THE NHC FORECAST CALLS FOR A SLIGHT STRENGTHENING. IT IS ANTICIPATED THAT KAREN WILL BE ON A WEAKENING TREND BEYOND 48 HOURS...AND BECOME EXTRATROPICAL BY DAY 4. FIXES FROM THE HURRICANE HUNTER PLANES INDICATE THAT KAREN IS MOVING TOWARD THE NORTH-NORTHWEST OR 335 DEGREES AT 9 KNOTS. AS A NARROW RIDGE OVER FLORIDA WEAKENS OR SLIDES EASTWARD...AND A LARGE MID- TO UPPER-LEVEL TROUGH APPROACHES FROM THE WEST...THE CYCLONE WILL BEGIN TO MOVE SLOWLY NORTHWARD AND THEN RECURVE TO THE NORTHEAST WITH AN INCREASE IN FORWARD SPEED. THE OVERALL TRACK GUIDANCE SUGGESTS A TYPICAL RECURVATURE OVER THE CENTRAL GULF OF MEXICO AND SO DOES THE NHC FORECAST. IN FACT...THE OFFICIAL FORECAST IS VERY SIMILAR TO THE PREVIOUS ONE...AND FOLLOWS VERY CLOSELY THE MULTI-MODEL CONSENSUS. GIVEN THE CURRENT NHC FORECAST...NO CHANGE IN WATCHES AND WARNINGS IS NECESSARY AT THIS TIME...BUT THIS WILL BE REVISITED AS KAREN PROGRESSES NORTHWARD ACROSS THE CENTRAL GULF OF MEXICO. FORECAST POSITIONS AND MAX WINDS INIT 04/0300Z 24.2N 89.0W 55 KT 65 MPH 12H 04/1200Z 25.5N 89.7W 55 KT 65 MPH 24H 05/0000Z 26.9N 90.0W 60 KT 70 MPH 36H 05/1200Z 28.0N 90.0W 60 KT 70 MPH 48H 06/0000Z 29.2N 89.0W 60 KT 70 MPH 72H 07/0000Z 32.5N 84.5W 35 KT 40 MPH...INLAND 96H 08/0000Z 36.5N 79.5W 25 KT 30 MPH...POST-TROP/EXTRATROP 120H 09/0000Z...DISSIPATED $$ FORECASTER AVILA

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Tropical Storm KAREN Forecast Discussion Number 3

2013-10-03 22:50:42| National Hurricane Center (Atlantic)

Issued at 400 PM CDT THU OCT 03 2013 000 WTNT42 KNHC 032050 TCDAT2 TROPICAL STORM KAREN DISCUSSION NUMBER 3 NWS NATIONAL HURRICANE CENTER MIAMI FL AL122013 400 PM CDT THU OCT 03 2013 THE SATELLITE APPEARANCE OF KAREN REMAINS LESS THAN IMPRESSIVE...AS THE CENTER HAS BEEN PARTIALLY EXPOSED TO THE WEST OF THE REMAINING DEEP CONVECTION. THE SHIPS MODEL CONTINUES TO ANALYZE ABOUT 20 KT OF SOUTHWESTERLY SHEAR OVER KAREN...AND DRY AIR IS PRESENT IN THE MID/UPPER LEVELS OVER THE WESTERN SEMICIRCLE. DESPITE THESE NEGATIVE FACTORS...KAREN CONTINUES TO MAINTAIN ITS INTENSITY. THE NOAA HURRICANE HUNTERS JUST MEASURED A CENTRAL PRESSURE OF 999 MB...AND FLIGHT-LEVEL AND SFMR WINDS FROM BOTH THE NOAA AND AIR FORCE RESERVE AIRCRAFT SUPPORT MAINTAINING THE INITIAL INTENSITY AT 55 KT. MODERATE SHEAR IS EXPECTED TO CONTINUE...AND ONLY GRADUAL STRENGTHENING IS EXPECTED BEFORE THE SHEAR INCREASES FURTHER IN ABOUT 48 HOURS. SOME WEAKENING IS THEN ANTICIPATED AS KAREN APPROACHES THE GULF COAST...BUT THE STORM COULD STILL BE NEAR HURRICANE STRENGTH AT LANDFALL. THE NHC FORECAST IS CLOSE TO THE SHIPS AND LGEM MODELS AND THE IVCN INTENSITY CONSENSUS THROUGH THE PERIOD. KAREN SHOULD BE EXTRATROPICAL BY ABOUT 4 DAYS AND ABSORBED BY DAY 5...IF NOT SOONER. THE INITIAL MOTION ESTIMATE IS A MORE CONFIDENT 330/10 BASED ON AIRCRAFT FIXES AND SATELLITE IMAGERY. THE TRACK FORECAST REASONING REMAINS UNCHANGED...AS KAREN WILL MOVE AROUND THE PERIPHERY OF THE SUBTROPICAL RIDGE DURING THE NEXT DAY OR SO...WITH A DECREASE IN FORWARD SPEED AS A MID-LEVEL RIDGE BUILDS BRIEFLY TO THE NORTHEAST OF THE CYCLONE. A NORTHEASTWARD ACCELERATION IS EXPECTED AFTER 48 HOURS AHEAD OF A MID/UPPER-LEVEL TROUGH. THE TRACK GUIDANCE HAS AGAIN SHIFTED A LITTLE TO THE WEST THIS CYCLE...AND THERE REMAINS CONSIDERABLE EAST/WEST SPREAD...WITH THE HWRF AND GFS TO THE EAST AND THE ECMWF TO THE WEST. THE NHC TRACK HAS BEEN ADJUSTED TO THE WEST ABOUT A HALF A DEGREE BUT STILL LIES A LITTLE TO THE EAST OF THE LATEST TCVA CONSENSUS...AND IS CLOSE TO THE FSU SUPERENSEMBLE THROUGH LANDFALL. THE 34-KT WIND RADII HAVE BEEN ADJUSTED OUTWARD IN THE EASTERN SEMICIRCLE BASED ON AN EARLIER ASCAT PASS. GIVEN THE NEW NHC TRACK AND INTENSITY FORECAST...A TROPICAL STORM WARNING HAS BEEN ISSUED FOR A PORTION OF SOUTHEASTERN LOUISIANA. FORECAST POSITIONS AND MAX WINDS INIT 03/2100Z 23.3N 88.5W 55 KT 65 MPH 12H 04/0600Z 24.6N 89.3W 60 KT 70 MPH 24H 04/1800Z 26.2N 89.9W 60 KT 70 MPH 36H 05/0600Z 27.6N 89.8W 65 KT 75 MPH 48H 05/1800Z 28.8N 89.3W 60 KT 70 MPH 72H 06/1800Z 32.0N 86.0W 40 KT 45 MPH...INLAND 96H 07/1800Z 36.0N 80.5W 25 KT 30 MPH...POST-TROP/EXTRATROP 120H 08/1800Z...ABSORBED BY FRONT $$ FORECASTER BRENNAN

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Post-Tropical Cyclone JERRY Forecast Discussion Number 20

2013-10-03 22:32:03| National Hurricane Center (Atlantic)

Issued at 500 PM AST THU OCT 03 2013 000 WTNT41 KNHC 032031 TCDAT1 POST-TROPICAL CYCLONE JERRY DISCUSSION NUMBER 20 NWS NATIONAL HURRICANE CENTER MIAMI FL AL112013 500 PM AST THU OCT 03 2013 JERRY LACKS SUFFICIENT ORGANIZED DEEP CONVECTION TO QUALIFY AS A TROPICAL CYCLONE...AND IS THEREFORE BEING DESIGNATED AS A REMNANT LOW PRESSURE SYSTEM. THE INTENSITY ESTIMATE REMAINS AT 30 KT... ALTHOUGH THIS MAY BE GENEROUS. THE LOW WILL CONTINUE TO TRAVERSE PROGRESSIVELY COOLER WATERS...AND VERTICAL SHEAR OVER THE SYSTEM IS FORECAST TO INCREASE TO NEAR 25 KT IN 48 HOURS. REGENERATION IS UNLIKELY AND BASED ON A BLEND OF THE GFS AND ECMWF SOLUTIONS...THE SYSTEM IS EXPECTED TO OPEN UP INTO A TROUGH AFTER 48 HOURS. INITIAL MOTION IS A LITTLE FASTER...060/12. POST-TROPICAL JERRY IS FORECAST TO MOVE EAST-NORTHEASTWARD TO NORTHEASTWARD AHEAD OF A BROAD MID-LATITUDE TROUGH. THE OFFICIAL TRACK FORECAST IS VERY SIMILAR TO THE PREVIOUS ONE AND LIES BETWEEN THE GFS PREDICTION AND THE MULTI-MODEL CONSENSUS. THIS IS THE LAST ADVISORY ON JERRY ISSUED BY THE NATIONAL HURRICANE CENTER. ADDITIONAL INFORMATION ON THIS SYSTEM CAN BE FOUND IN HIGH SEAS FORECASTS ISSUED BY THE NATIONAL WEATHER SERVICE...UNDER AWIPS HEADER NFDHSFAT1 AND WMO HEADER FZNT01 KWBC. FORECAST POSITIONS AND MAX WINDS INIT 03/2100Z 31.8N 38.7W 30 KT 35 MPH...POST-TROP/REMNT LOW 12H 04/0600Z 32.6N 36.7W 30 KT 35 MPH...POST-TROP/REMNT LOW 24H 04/1800Z 33.7N 34.1W 30 KT 35 MPH...POST-TROP/REMNT LOW 36H 05/0600Z 34.8N 32.0W 25 KT 30 MPH...POST-TROP/REMNT LOW 48H 05/1800Z 36.0N 30.5W 25 KT 30 MPH...POST-TROP/REMNT LOW 72H 06/1800Z...DISSIPATED $$ FORECASTER PASCH

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Tropical Storm KAREN Forecast Discussion Number 2

2013-10-03 16:39:03| National Hurricane Center (Atlantic)

Issued at 1000 AM CDT THU OCT 03 2013 000 WTNT42 KNHC 031438 TCDAT2 TROPICAL STORM KAREN DISCUSSION NUMBER 2 NWS NATIONAL HURRICANE CENTER MIAMI FL AL122013 1000 AM CDT THU OCT 03 2013 KAREN CONTINUES TO HAVE A SOMEWHAT SHEARED APPEARANCE ON SATELLITE IMAGERY...WITH THE DEEP CONVECTION DISPLACED TO THE NORTHEAST OF THE LOW-LEVEL CENTER. THIS IS CONSISTENT WITH THE 20 OR SO KT OF SHEAR ANALYZED OVER THE CYCLONE BY THE SHIPS MODEL. THE INITIAL INTENSITY IS RAISED TO 55 KT BASED ON SEVERAL BIAS-CORRECTED SFMR WINDS IN THE 50-55 KT RANGE REPORTED BY THE AIRCRAFT. WITH MODERATE SHEAR EXPECTED TO CONTINUE...ONLY GRADUAL STRENGTHENING IS EXPECTED BEFORE THE SHEAR INCREASES FURTHER IN ABOUT 48 HOURS. SOME WEAKENING IS ANTICIPATED AS KAREN APPROACHES THE GULF COAST...BUT THE STORM COULD STILL BE NEAR HURRICANE STRENGTH AT LANDFALL. THE NHC FORECAST IS CLOSE TO THE SHIPS AND LGEM MODELS THROUGH THE PERIOD. KAREN SHOULD BE INVOLVED WITH A FRONTAL ZONE BY DAY 4 AND ABSORBED BY THE FRONT BY DAY 5. THE INITIAL MOTION ESTIMATE IS STILL A RELATIVELY UNCERTAIN 330/10. THE TRACK FORECAST REASONINS HAS NOT CHANGED...AS KAREN WILL MOVE AROUND THE PERIPHERY OF THE SUBTROPICAL RIDGE DURING THE NEXT DAY OR SO AND THEN ACCELERATE NORTHEASTWARD AHEAD OF A MID/UPPER-LEVEL TROUGH. THERE REMAINS CONSIDERABLE EAST/WEST SPREAD IN THE TRACK GUIDANCE...WITH THE GFS REMAINING WELL EAST OF THE OTHER GLOBAL MODELS AND ITS ENSEMBLE MEAN. THE TRACK GUIDANCE HAS SHIFTED A LITTLE TO THE WEST THIS CYCLE...AND THE NEW NHC TRACK IS CLOSE TO THE MULTI-MODEL CONSENSUS AND ABOUT A HALF A DEGREE LEFT OF THE PREVIOUS TRACK THROUGH 48 HOURS. NOTE THAT A STRONGER STORM WOULD LIKELY MOVER FARTHER EAST...WHILE A WEAKER SYSTEM WOULD BE MORE LIKELY TO TAKE A TRACK FARTHER WEST. FORECAST POSITIONS AND MAX WINDS INIT 03/1500Z 22.2N 87.9W 55 KT 65 MPH 12H 04/0000Z 23.8N 88.7W 60 KT 70 MPH 24H 04/1200Z 25.4N 89.4W 60 KT 70 MPH 36H 05/0000Z 26.9N 89.5W 65 KT 75 MPH 48H 05/1200Z 28.2N 89.1W 60 KT 70 MPH 72H 06/1200Z 31.0N 87.0W 45 KT 50 MPH...INLAND 96H 07/1200Z 35.0N 81.5W 25 KT 30 MPH...POST-TROP/EXTRATROP 120H 08/1200Z...ABSORBED BY FRONT $$ FORECASTER BRENNAN

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