TROPICAL DEPRESSION DANNY DISCUSSION NUMBER 12
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL AL052009
500 AM EDT SAT AUG 29 2009

SATELLITE IMAGES…SURFACE OBSERVATIONS AND DATA FROM AN AIR FORCE RECONNAISSANCE PLANE INDICATE THAT DANNY IS RAPIDLY BECOMING ABSORBED BY A FRONTAL LOW WHICH IS DEVELOPING OVER NORTH CAROLINA.

IN FACT…THE PLANE TRAVERSED THE POSSIBLE LOCATION OF DANNY A COUPLE TIMES AND DID NOT FIND ANY SIGNIFICANT CYCLONIC WIND SHIFT NOR DID IT MEASURE TROPICAL STORM FORCE WINDS AT THE SURFACE.

THEREFORE…ADVISORIES ON DANNY HAVE BEEN TERMINATED AND THE TROPICAL STORM WATCH HAS BEEN DISCONTINUED.

THE EXTRATROPICAL LOW WILL MOVE TOWARD THE NORTH-NORTHEAST AND THEN NORTHEAST AND ITS POTENTIAL IMPACTS WILL BE HANDLED WITH GALE WARNINGS AND OTHER PRODUCTS ISSUED BY LOCAL NWS OFFICES IN THAT REGION.

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

INITIAL 29/0900Z 34.3N 74.6W 30 KT…BECOMING ABSORBED
12HR VT 29/1800Z 38.0N 73.0W 35 KT…EXTRATROPICAL
24HR VT 30/0600Z 41.2N 69.2W 40 KT…EXTRATROPICAL
36HR VT 30/1800Z 46.2N 62.8W 40 KT…EXTRATROPICAL
48HR VT 31/0600Z 49.5N 56.0W 40 KT…EXTRATROPICAL
72HR VT 01/0600Z 54.5N 43.5W 40 KT…EXTRATROPICAL
96HR VT 02/0600Z 56.5N 27.0W 45 KT…EXTRATROPICAL
120HR VT 03/0600Z 57.0N 10.1W 50 KT…EXTRATROPICAL

DANNY REMAINS A POORLY ORGANIZED TROPICAL STORM. THE STRONGEST WINDS AND LARGEST AREAS OF CONVECTION ARE STILL WELL SOUTHEAST OF THE CENTER…ALTHOUGH SOME DISORGANIZED CONVECTION HAS RECENTLY FORMED NEAR THE CENTER.

JUST-RECEIVED QUIKSCAT DATA SHOWS ONE RELIABLE-LOOKING 35 KT VECTOR SOUTHEAST OF THE CENTER…SO THE INITIAL INTENSITY REMAINS 35 KT.

ANALYSES FROM CIMSS AT THE UNIVERSITY OF WISCONSIN INDICATE ABOUT 15 KT OF SOUTHWESTERLY VERTICAL WIND SHEAR AS DANNY IS BECOMING EMBEDDED IN FLOW BETWEEN AN UPPER-LEVEL ANTICYCLONE NEAR 26N71W AND THE POWERFUL UPPER-LEVEL TROUGH MOVING NORTHEASTWARD THROUGH THE SOUTHEASTERN UNITED STATES.

DANNY HAS CONTINUED ITS ERRATIC MOTION THIS EVENING. JUST BEFORE SUNSET…THE EXPOSED CENTER APPEARED TO BE MOVING NORTH-NORTHEASTWARD OR NORTHEASTWARD.

SINCE THEN…THE CENTER HAS DISAPPEARED UNDER CIRRUS CLOUDS…BUT IT SEEMS TO BE MOVING MORE NORTHWARD AT A FASTER PACE.

THE INITIAL MOTION IS AN UNCERTAIN 020/10. OTHER THAN THAT…THE TRACK FORECAST SCENARIO IS UNCHANGED.

TROPICA STORM DANNY SHOULD ACCELERATE INTO THE WESTERLIES…MOVING GENERALLY NORTH-NORTHEASTWARD FOR THE FIRST 24 HR OR SO…FOLLOWED BY A TURN TO THE NORTHEAST AND EVENTUALLY EAST-NORTHEASTWARD.

THE NEW FORECAST TRACK IS NUDGED TO THE EAST OF THE PREVIOUS TRACK BASED ON THE INITIAL POSITION AND MOTION…AND LIES ALONG THE LEFT EDGE OF THE TIGHTLY CLUSTERED TRACK GUIDANCE MODELS THROUGH 48 HR.

THE TRACK CALLS FOR THE CENTER TO PASS EAST OF CAPE HATTERAS IN ABOUT 12 HR…SOUTHEAST OF CAPE COD IN 24-30 HR…AND NEAR OR OVER NOVA SCOTIA AND NEWFOUNDLAND IN 36-48 HR.

DANNY IS ABOUT OUT OF TIME TO STRENGTHEN AS A TROPICAL CYCLONE…AS VERTICAL SHEAR OVER THE SYSTEM IS FORECAST TO INCREASE SIGNIFICANTLY OVER THE NEXT 12-24 HR.

AFTER THAT…THE SYSTEM SHOULD UNDERGO EXTRATROPICAL TRANSITION.

THE INTENSITY FORECAST IS THE SAME AS THE PREVIOUS ADVISORY…CALLING FOR A LITTLE INTENSIFICATION WHILE DANNY IS STILL TROPICAL…LITTLE CHANGE IN STRENGTH THROUGH EXTRATROPICAL TRANSITION…THEN SOME INTENSIFICATION AS AN EXTRATROPICAL LOW OVER THE NORTH ATLANTIC.

AN AIR FORCE RESERVE HURRICANE HUNTER AIRCRAFT SHOULD ARRIVE IN DANNY AROUND 06Z TO BETTER DETERMINE THE POSITION AND INTENSITY.

AS DANNY BECOMES EXTRATROPICAL…ITS EXPANDING WIND FIELD MAY IMPACT THE COAST OF NEW ENGLAND.

THESE POTENTIAL IMPACTS WILL BE HANDLED WITH GALE WARNINGS AND OTHER PRODUCTS ISSUED BY LOCAL NWS OFFICES IN THAT REGION.

TROPICAL STORM DANNY PATH – FORECAST POSITIONS AND MAX WINDS

INITIAL 29/0300Z 31.4N 74.9W 35 KT
12HR VT 29/1200Z 34.7N 73.8W 40 KT
24HR VT 30/0000Z 39.5N 70.1W 40 KT
36HR VT 30/1200Z 44.0N 64.5W 40 KT…EXTRATROPICAL
48HR VT 31/0000Z 47.3N 58.1W 40 KT…EXTRATROPICAL
72HR VT 01/0000Z 51.5N 45.0W 40 KT…EXTRATROPICAL
96HR VT 02/0000Z 53.5N 30.0W 45 KT…EXTRATROPICAL
120HR VT 03/0000Z 56.0N 14.0W 50 KT…EXTRATROPICAL

…DANNY NOW MOVING NORTH-NORTHEASTWARD WITH NO CHANGE IN ORGANIZATION…

A TROPICAL STORM WATCH IS IN EFFECT FOR THE NORTH CAROLINA COAST FROM CAPE LOOKOUT NORTHWARD TO DUCK…INCLUDING THE PAMLICO AND ALBEMARLE SOUNDS.

A TROPICAL STORM WATCH MEANS THAT TROPICAL STORM CONDITIONS ARE POSSIBLE WITHIN THE WATCH AREA…IN THIS CASE…WITHIN 24 HOURS.

A TROPICAL STORM WARNING MAY BE REQUIRED FOR PORTIONS OF THIS AREA TONIGHT.

INTERESTS ELSEWHERE FROM THE CAROLINAS NORTHWARD TO NEW ENGLAND AND THE CANADIAN MARITIMES SHOULD MONITOR THE PROGRESS OF DANNY.

AT 800 PM EDT…0000 UTC…THE CENTER OF TROPICAL STORM DANNY WAS LOCATED NEAR LATITUDE 30.9 NORTH…LONGITUDE 75.1 WEST OR ABOUT 300 MILES…480 KM…SOUTH OF CAPE HATTERAS NORTH CAROLINA AND ABOUT 765 MILES…1230 KM…SOUTH-SOUTHWEST OF NANTUCKET MASSACHUSETTS.

DANNY IS MOVING TOWARD THE NORTH-NORTHEAST NEAR 8 MPH…13 KM/HR.

A GENERAL NORTHWARD TO NORTH-NORTHEASTWARD MOTION IS EXPECTED WITH AN INCREASE IN FORWARD SPEED DURING THE NEXT COUPLE OF DAYS.

ON THIS TRACK…THE CENTER OF DANNY IS EXPECTED TO PASS OFFSHORE OF THE OUTER BANKS OF NORTH CAROLINA EARLY SATURDAY…PASS OFFSHORE OF SOUTHEASTERN NEW ENGLAND ON SATURDAY NIGHT AND MOVE NEAR THE CANADIAN MARITIMES SUNDAY.

MAXIMUM SUSTAINED WINDS ARE NEAR 40 MPH…65 KM/HR…WITH HIGHER GUSTS.

SOME SLIGHT STRENGTHENING IS POSSIBLE TONIGHT…WITH LITTLE CHANGE IN INTENSITY EXPECTED ON SATURDAY.

DANNY IS EXPECTED TO BECOME EXTRATROPICAL ON SATURDAY NIGHT.

TROPICAL STORM FORCE WINDS EXTEND OUTWARD UP TO 175 MILES…280 KM MOSTLY TO THE SOUTHEAST OF THE CENTER.

THE ESTIMATED MINIMUM CENTRAL PRESSURE IS 1006 MB…29.71 INCHES.

LARGE SWELLS FROM DANNY ARE EXPECTED TO PRODUCE DANGEROUS SURF CONDITIONS AND LIFE-THREATENING RIP CURRENTS ALONG THE U.S. EAST COAST DURING THE NEXT DAY OR TWO.

…SUMMARY OF 800 PM EDT INFORMATION…
LOCATION…30.9N 75.1W
MAXIMUM SUSTAINED WINDS…40 MPH
PRESENT MOVEMENT…NORTH-NORTHEAST OR 30 DEGREES AT 8 MPH
MINIMUM CENTRAL PRESSURE…1006 MB

THE NEXT ADVISORY WILL BE ISSUED BY THE NATIONAL
HURRICANE CENTER AT 1100 PM EDT.

AFTER STALLING EARLIER THIS AFTERNOON…THE CENTER OF DANNY IS FINALLY MOVING SLOWLY NORTHWARD OR NORTH-NORTHEASTWARD.

DATA FROM AN AIR FORCE RESERVE HURRICANE HUNTER AIRCRAFT SUGGEST THAT DANNY IS STILL A MINIMAL TROPICAL STORM…BASED ON A 33-KT OBSERVATION FROM THE SFMR IN THE SOUTHEASTERN QUADRANT.

THE INTENSITY FORECAST SHOWS THE POSSIBILITY FOR A LITTLE STRENGTHENING IN THE SHORT TERM…AS THE INCREASING UPPER-LEVEL DIVERGENCE COULD SUPPORT THE REDEVELOPMENT OF CONVECTION NEAR THE CENTER.

HOWEVER…BY 24 HOURS…DANNY WILL BE MOVING INTO A VERY UNFAVORABLE ENVIRONMENT FOR A TROPICAL CYCLONE…WITH THE SHIPS MODEL SHOWING WIND SHEAR INCREASING TO 35 KT BY THAT TIME.

BY 36 HOURS…DANNY WILL BE OVER SSTS OF NEAR 20C…AND INTERACTING WITH THE DEEP-LAYER BAROCLINIC TROUGH OVER THE EASTERN U.S.

MOST OF THE LATEST GLOBAL MODELS AND PHASE SPACE DIAGRAMS SHOW THAT DANNY WILL BE EXTRATROPICAL BY THAT TIME.

THERE IS THE POTENTIAL FOR SOME INTENSIFICATION OF DANNY LATE IN THE FORECAST PERIOD AS AN EXTRATROPICAL CYCLONE OVER THE NORTH ATLANTIC.

THE GUIDANCE WAS INITIALIZED WITH A LONG TERM MOTION OF 315/08…AND REMAINS IS GOOD AGREEMENT ON THE RAPID ACCELERATION OF DANNY NORTHWARD AND NORTH-NORTHEASTWARD.

IN FACT…THE MODEL SPREAD IS SMALLER NOW THAN IT WAS EARLIER TODAY. THE OFFICIAL TRACK IS SLOWER THAN THE MODEL CONSENSUS THROUGH MOST OF THE PERIOD DUE TO THE SLOW INITIAL MOTION.

FROM 24 TO 36 HOURS…THE NEW FORECAST IS SHIFTED TO THE RIGHT OF THE PREVIOUS FORECAST TRACK…BUT DANNY IS STILL EXPECTED TO MOVE CLOSE TO THE SOUTHEASTERN COAST OF NEW ENGLAND AND APPROACH NOVA SCOTIA IN 36-48 HOURS.

DATA FROM THE AIRCRAFT SUGGEST THAT THE ONLY 34-KT WINDS ARE LOCATED IN THE SOUTHEASTERN QUADRANT.

THE LACK OF WINDS ON THE WEST SIDE OF DANNY LESSEN THE THREAT FOR TROPICAL STORM WIND REACHING THE NORTH CAROLINA OUTER BANKS.

HOWEVER…THE WATCH IS LEFT IN PLACE IN CASE THE WIND FIELD BECOMES BETTER DEFINED ON THE WESTERN SIDE OF DANNY.

AS DANNY BECOMES EXTRATROPICAL…ITS EXPANDING WIND FIELD MAY IMPACT THE COAST OF NEW ENGLAND.

THESE POTENTIAL IMPACTS WILL BE HANDLED WITH GALE WARNINGS AND OTHER PRODUCTS ISSUED BY LOCAL NWS OFFICES IN THAT REGION.

TROPICAL STORM DANNY – FORECAST POSITIONS AND MAX WINDS

INITIAL 28/2100Z 30.4N 75.4W 35 KT
12HR VT 29/0600Z 32.7N 75.8W 40 KT
24HR VT 29/1800Z 37.3N 73.2W 40 KT
36HR VT 30/0600Z 41.9N 68.2W 40 KT…EXTRATROPICAL
48HR VT 30/1800Z 46.5N 61.4W 40 KT…EXTRATROPICAL
72HR VT 31/1800Z 50.5N 49.5W 40 KT…EXTRATROPICAL
96HR VT 01/1800Z 53.0N 35.0W 45 KT…EXTRATROPICAL
120HR VT 02/1800Z 55.0N 22.0W 50 KT…EXTRATROPICAL

TROPICAL STORM DANNY DISCUSSION NUMBER 9
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL AL052009
1100 AM EDT FRI AUG 28 2009

THE CENTER OF DANNY REMAINS EXPOSED THIS MORNING…AND OVER THE PAST COUPLE OF HOURS HAS BEEN MOVING ALMOST DUE WESTWARD AWAY FROM THE DEEP CONVECTION.

NOAA BUOY 41047 WELL SOUTHEAST OF THE CENTER REPORTED A 1-MINUTE PEAK SUSTAINED WIND OF 31 KT AT 1100 UTC.

THE INITIAL INTENSITY IS HELD AT 35 KT…ASSUMING THAT HIGHER WINDS STILL EXIST WELL EAST OF THE CENTER.

AN AIR FORCE RESERVE HURRICANE HUNTER AIRCRAFT WILL BE INVESTIGATING DANNY LATER THIS AFTERNOON TO PROVIDE MORE INFORMATION ON ITS INTENSITY AND STRUCTURE.

THE INITIAL MOTION ESTIMATE IS 325/9…A COMPROMISE BETWEEN THE SHORT TERM WESTWARD MOTION AND THE LONGER TERM NORTH-NORTHWESTWARD MOTION OBSERVED OVERNIGHT.

THE FORECAST IS ADJUSTED TOWARD THE WEST DUE TO THE INITIAL MOTION AND ACTUALLY LIES WEST OF ALL THE DYNAMICAL MODELS AT 12 HOURS…AS THESE MODELS IMMEDIATELY TURN DANNY NORTHWARD.

LATER IN THE FORECAST PERIOD…THE TRACK IS VERY CLOSE TO THE TVCN MULTI-MODEL CONSENSUS.

BY 36 HOURS…THIS POSITION IS JUST SOUTH OF THE COAST OF MASSACHUSETTS…WITH THE GFS…ECMWF…AND GFS ENSEMBLE MEAN SIGNIFICANTLY LEFT OF THE CONSENSUS…AND MOST OF THE OTHER GUIDANCE CLUSTERED TO THE RIGHT.

BEYOND THAT TIME…DANNY SHOULD BE ACCELERATING TOWARD THE NORTHEAST THROUGH THE CANADIAN MARITIMES AND EAST-NORTHEASTWARD INTO THE NORTH ATLANTIC.

IT SHOULD BE NOTED THAT THERE ARE A COUPLE OF ALTERNATIVE SCENARIOS THAT COULD OCCUR.

THE SHALLOW BAM MODEL REPRESENTS AN EVEN MORE WESTWARD TRACK THAT COULD OCCUR IF DANNY LOSES ALL OF ITS DEEP CONVECTION.

IT IS ALSO POSSIBLE THAT A NEW CENTER COULD RE-FORM UNDER THE DEEP CONVECTION FARTHER EAST.

EITHER OF THESE SCENARIOS WOULD LIKELY REDUCE THE THREAT TO THE U.S. EAST COAST.

THE INTENSITY FORECAST SHOWS THE POSSIBILITY FOR A LITTLE STRENGTHENING IN THE NEXT 12 HOURS…BUT AFTER THAT TIME THE CYCLONE WILL BE MOVING INTO A VERY UNFAVORABLE ENVIRONMENT…WITH THE SHIPS MODEL SHOWING WIND SHEAR INCREASING TO OVER 30 KT BY 24 HOURS AS DANNY INTERACTS WITH A DEEP-LAYER TROUGH OVER THE EASTERN UNITED STATES.

THE GLOBAL MODELS AND PHASE SPACE DIAGRAMS SHOW THAT DANNY WILL BEGIN EXTRATROPICAL TRANSITION BEGINNING BY 48 HOURS…AND THAT THE CYCLONE WILL BE FULLY EXTRATROPICAL BY 72 HOURS.

THIS EVOLUTION IS REFLECTED IN THE OFFICIAL FORECAST…WHICH SHOWS AN EXPANDING WIND FIELD AS DANNY MOVES FROM THE CANADIAN MARITIMES INTO THE NORTH ATLANTIC.

DESPITE THE WESTWARD SHIFT IN THE TRACK…A TROPICAL STORM WARNING WILL NOT BE ISSUED FOR THE COAST OF NORTH CAROLINA AT THIS TIME…DUE TO THE CURRENT AND EXPECTED LIMITED EXTENT OF TROPICAL STORM FORCE WINDS ON THE WEST SIDE OF THE CIRCULATION.

THE TROPICAL STORM WATCH REMAINS IN EFFECT IN CASE THE WIND FIELD BECOMES BETTER DEFINED ON THE WESTERN SIDE OF DANNY OR IF THE FORECAST CONTINUES TO SHIFT WESTWARD.

A TROPICAL STORM WATCH MAY ALSO BE NEEDED FOR PORTIONS OF THE COAST OF NEW ENGLAND LATER TODAY.

TROPICAL STORM DANNY PATH – FORECAST POSITIONS AND MAX WINDS

INITIAL 28/1500Z 30.1N 75.5W 35 KT
12HR VT 29/0000Z 32.5N 75.7W 40 KT
24HR VT 29/1200Z 36.2N 74.1W 40 KT
36HR VT 30/0000Z 40.7N 70.7W 40 KT
48HR VT 30/1200Z 44.6N 65.1W 40 KT…INLAND
72HR VT 31/1200Z 49.6N 52.5W 40 KT…EXTRATROPICAL
96HR VT 01/1200Z 52.5N 38.0W 40 KT…EXTRATROPICAL
120HR VT 02/1200Z 54.5N 21.5W 45 KT…EXTRATROPICAL

TROPICAL STORM DANNY DISCUSSION NUMBER 8
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL AL052009
500 AM EDT FRI AUG 28 2009

AN AIR FORCE RECONNAISSANCE PLANE HAS BEEN IN THE AREA OF DANNY SINCE AROUND 05 UTC AND FOUND THAT DANNY IS BARELY A TROPICAL STORM…WITH THE STRONGEST WINDS CONFINED ONLY TO THE NORTHEAST OF THE CENTER.

THE INITIAL INTENSITY HAS BEEN LOWERED TO 35 KNOTS.

AFTER SEVERAL HOURS OF THE CENTER BEING COMPLETELY EXPOSED DUE TO STRONG WESTERLY SHEAR…A NEW ROUND OF CONVECTION HAS RECENTLY DEVELOPED NEAR THE CENTER.

THE STRONG SHEAR NEARBY MOST LIKELY WILL REMOVE THE CONVECTION ONCE AGAIN AT ANY TIME.

SINCE GLOBAL MODELS ARE BUILDING A WEAK UPPER-LEVEL RIDGE OVER THE CYCLONE WITHIN THE NEXT 12 TO 24 HOURS…THERE IS A SMALL OPPORTUNITY FOR SLIGHT STRENGTHENING DURING THIS PERIOD.

THEREAFTER…WITH A LARGE TROUGH APPROACHING DANNY…THE MOST LIKELY SCENARIO IS THAT THE CYCLONE WILL INTERACT WITH THE MID-LATITUDE TROUGH AND BEGIN THE TRANSITION TO AN EXTRATROPICAL CYCLONE BY 48 HOURS.

THE CENTER HAS BEEN MOVING BETWEEN THE NORTHWEST AND NORTH-NORTHWEST DURING THE PAST FEW HOURS…BUT THE BEST LONG-TERM ESTIMATE OF THE INITIAL MOTION IS 330 DEGREES AT 8 KT.

THE LARGE TROUGH ALONG THE EASTERN UNITED STATES WILL FORCE DANNY TO MOVE TOWARD THE NORTH AND THEN NORTHEAST WITH INCREASING FORWARD SPEED AFTER 24 HOURS.

MOST OF THE TRACK MODELS KEEP THE CENTER OF DANNY AWAY FROM THE UNITED STATES EAST COAST…AND SINCE THE TROPICAL STORM FORCE WINDS ARE CONFINED TO THE EASTERN PORTION OF THE CYCLONE…IT IS NOT NECESSARY TO ISSUE A TROPICAL STORM WARNING FOR THE REGION CURRENTLY UNDER A TROPICAL STORM WATCH.

THE TROPICAL STORM WATCH REMAINS IN EFFECT IN CASE THE WIND FIELD BECOMES BETTER DEFINED ON THE WESTERN SIDE OF DANNY DURING THE NEXT SEVERAL HOURS OR THE FORECAST UNEXPECTEDLY SHIFTS TO THE WEST.

TROPICAL STORM DANNY FORECAST POSITIONS AND MAX WINDS

INITIAL 28/0900Z 29.5N 74.4W 35 KT
12HR VT 28/1800Z 31.3N 74.7W 40 KT
24HR VT 29/0600Z 34.2N 74.0W 45 KT
36HR VT 29/1800Z 38.5N 71.5W 40 KT
48HR VT 30/0600Z 42.5N 67.0W 40 KT
72HR VT 31/0600Z 47.5N 59.0W 40 KT…EXTRATROPICAL
96HR VT 01/0600Z 52.0N 47.0W 40 KT…EXTRATROPICAL
120HR VT 02/0600Z 54.0N 26.0W 45 KT…EXTRATROPICAL

REPORTS FROM AN AIR FORCE RESERVE HURRICANE HUNTER AIRCRAFT INDICATE THAT THE CIRCULATION OF DANNY HAS BECOME BETTER DEFINED TODAY…WITH STRONGER WINDS IN THE PREVIOUSLY WEAK SOUTHWESTERN QUADRANT.

ASIDE FROM THAT…THE CYCLONE REMAINS VERY DISORGANIZED.

THE MAIN CONVECTION IS IN A LINE 130-170 N MI EAST THROUGH SOUTH OF THE CENTER…AND THE STRONGEST WINDS ARE 100 N MI OR MORE FROM THE CENTER OVER THE NORTHERN SEMICIRCLE.

THE AIRCRAFT DATA…AS WELL AS DATA FROM THE QUIKSCAT AND ASCAT SCATTEROMETERS…SUGGEST THAT THE MAXIMUM WINDS HAVE DECREASED TO 40-45 KT.

THE INITIAL INTENSITY WILL BE REDUCED TO 45 KT.

THE CENTER HAS MOVED SLOWLY WESTWARD SINCE SUNRISE…WITH THE INITIAL MOTION ESTIMATED AT 270/2.

THE TRACK GUIDANCE MODELS REMAIN IN EXCELLENT AGREEMENT THAT DANNY SHOULD TURN NORTHWARD OVER THE NEXT 24-36 HR IN ADVANCE OF A COMPLEX DEEP-LAYER TROUGH MOVING INTO THE EASTERN UNITED STATES.

AFTER THAT…THE STORM SHOULD ACCELERATE NORTHEASTWARD INTO THE WESTERLIES…PASSING NEAR OR OVER CAPE HATTERAS…SOUTHEASTERN NEW ENGLAND…AND THE CANADIAN MARITIMES ON ITS WAY INTO THE NORTH ATLANTIC.

WITH THE MORE WESTERLY INITIAL POSITION…THE TRACK GUIDANCE ENVELOPE HAS SHIFTED SOMEWHAT WESTWARD DURING THE FIRST 48 HR…AND THE NEW FORECAST TRACK IS ADJUSTED WESTWARD AS WELL.

WHILE THE TRACK IS STILL DOWN THE MIDDLE OF THE GUIDANCE ENVELOPE…THE GFS…UKMET…NOGAPS…AND CANADIAN MODELS ARE ALL TO THE LEFT OF THE NEW TRACK.

SOME ADDITIONAL ADJUSTMENT TOWARD THE LEFT…TOWARD THE EAST COAST OF THE U. S….MAY BE REQUIRED IF THIS TREND CONTINUES.

DANNY REMAINS IN AN AREA OF UPPER-LEVEL CONFLUENT FLOW ASSOCIATED WITH THE PERSISTENT CYCLONIC SHEAR AXIS SEEN IN WATER VAPOR IMAGERY.

IN ADDITION…BOTH WATER VAPOR IMAGERY AND SSM/IS TOTAL PRECIPITABLE WATER IMAGERY SUGGEST THAT THE ENVIRONMENT NEAR DANNY IS DRY.

THESE FACTORS…COMBINED WITH THE CURRENT LACK OF ORGANIZATION…SUGGESTS THAT STRENGTHENING WILL BE SLOW AT BEST DURING THE NEXT 24 HR.

THERE IS A WINDOW OF OPPORTUNITY FOR DANNY TO STRENGTHEN FROM 24-36 HR AS IT IS FORECAST TO MOVE UNDER AN UPPER-LEVEL ANTICYCLONE.

AFTER THAT…IT WILL ENCOUNTER STRONG SOUTHWESTERLY FLOW ASSOCIATED WITH THE DEEP-LAYER TROUGH…WHICH SHOULD CAUSE WEAKENING AND EXTRATROPICAL TRANSITION.

THE NEW INTENSITY FORECAST CALLS FOR DANNY TO NOT REACH HURRICANE STRENGTH…WITH A PEAK INTENSITY OF 60 KT IN 48 HR.

IT SHOULD BE NOTED THAT THE GFDL AND HWRF STILL FORECAST DANNY TO BECOME A HURRICANE BY 36 HR.

HURRICANE DANNY FORECAST POSITIONS AND MAX WINDS

INITIAL 27/2100Z 27.5N 73.5W 45 KT
12HR VT 28/0600Z 28.5N 74.7W 45 KT
24HR VT 28/1800Z 30.7N 75.0W 50 KT
36HR VT 29/0600Z 34.4N 74.1W 55 KT
48HR VT 29/1800Z 38.8N 71.6W 60 KT
72HR VT 30/1800Z 46.5N 61.5W 50 KT…EXTRATROPICAL
96HR VT 31/1800Z 50.0N 49.0W 40 KT…EXTRATROPICAL
120HR VT 01/1800Z 51.0N 32.0W 35 KT…EXTRATROPICAL

TROPICAL STORM DANNY DISCUSSION NUMBER 5
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL AL052009
1100 AM EDT THU AUG 27 2009

DANNY HAS BECOME A LITTLE BETTER ORGANIZED THIS MORNING.

THE LOW-LEVEL CIRCULATION LOOKS BETTER DEFINED THAN IT DID YESTERDAY…AND THE CONVECTION IS CLOSER TO THE CENTER.

THAT BEING SAID…THE CENTER IS STILL EXPOSED…THE CONVECTION HAS MORE OF A LINEAR CHARACTER THAN THE CURVED BANDS CHARACTERISTIC OF A TROPICAL CYCLONE…AND THE STRONGEST WINDS ARE STILL WELL REMOVED FROM THE CENTER.

THE INITIAL INTENSITY IS HELD AT 50 KT PENDING THE NEXT AIR FORCE RESERVE HURRICANE HUNTER MISSION AT 18Z…ALTHOUGH RECENT QUIKSCAT DATA SUGGESTS THIS COULD BE A LITTLE GENEROUS.

THE EXPOSED LOW-LEVEL CENTER HAS BEEN MOVING ALMOST DUE WESTWARD FOR THE PAST FEW HOURS.

IT IS UNCLEAR IF THIS IS REPRESENTATIVE OF THE ACTUAL MOTION OF DANNY OR A SHORT-TERM TREND.

SO…THE INITIAL MOTION IS AN UNCERTAIN 310/11.

DESPITE THE PROBLEMATIC INITIAL MOTION…THE TRACK GUIDANCE MODELS ARE IN EXCELLENT AGREEMENT THAT DANNY SHOULD TURN NORTHWARD OVER THE NEXT 24-36 HR IN ADVANCE OF A COMPLEX DEEP-LAYER TROUGH MOVING INTO THE EASTERN UNITED STATES.

AFTER THAT…THE STORM SHOULD ACCELERATE NORTHEASTWARD INTO THE WESTERLIES…PASSING NEAR OR OVER NEW ENGLAND AND THE CANADIAN MARITIMES ON ITS WAY INTO THE NORTH ATLANTIC.

THE NAM…NOGAPS…AND CANADIAN MODELS ARE ON THE LEFT SIDE OF THE GUIDANCE ENVELOPE… CALLING FOR THE CENTER TO PASS NEAR CAPE HATTERAS AND THEN OVER NEW ENGLAND.

THE GFS…GFDL…AND HWRF ARE ON THE RIGHT SIDE…CALLING FOR THE CENTER TO STAY OFFSHORE UNTIL IT REACHES NOVA SCOTIA.

THE NEW FORECAST TRACK IS ADJUSTED TO THE LEFT OF THE PREVIOUS TRACK FOR THE FIRST 48 HR BASED ON THE INITIAL POSITION AND MOTION…AND IT LIES DOWN THE MIDDLE OF THE GUIDANCE ENVELOPE.

WHILE THE FORECAST TRACK DOES NOT CURRENTLY SHOW DANNY MAKING LANDFALL IN THE UNITED STATES…ADDITIONAL MOTION TO THE LEFT OF THE TRACK COULD BRING THE CENTER NEAR OR OVER THE U. S. EASTERN SEABOARD.

DANNY IS CURRENTLY IN AN AREA OF UPPER-LEVEL CONFLUENT FLOW ASSOCIATED WITH THE PERSISTENT CYCLONIC SHEAR AXIS SEEN IN WATER VAPOR IMAGERY.

THE LARGE-SCALE MODELS FORECAST THIS FEATURE TO BE REPLACED BY AN UPPER-LEVEL ANTICYCLONE DURING THE NEXT 24-30 HR…AND IF THIS VERIFIES IT WILL GIVE DANNY ITS BEST CHANCE TO STRENGTHEN.

BASED ON THIS…THE INTENSITY FORECAST CALLS FOR DANNY TO STRENGTHEN DURING THE 24-48 HR PERIOD…WITH A PEAK INTENSITY OF 65 KT.

THE GUIDANCE AGREES THAT DANNY SHOULD START LOSING TROPICAL CHARACTERISTICS AND INTENSITY AFTER 48 HR AS IT BECOMES EMBEDDED IN A STRONG BAROCLINIC ENVIRONMENT.

OVERALL…THE INTENSITY FORECAST IS IN BEST AGREEMENT WITH THE INTENSITY CONSENSUS…WITH THE PEAK INTENSITY BELOW THAT OF THE HWRF AND GFDL MODELS.

HURRICANE DANNY FORECAST POSITIONS AND MAX WINDS

INITIAL 27/1500Z 27.5N 73.1W 50 KT
12HR VT 28/0000Z 28.7N 73.9W 50 KT
24HR VT 28/1200Z 30.3N 74.5W 55 KT
36HR VT 29/0000Z 33.2N 74.3W 60 KT
48HR VT 29/1200Z 36.9N 72.4W 65 KT
72HR VT 30/1200Z 45.0N 64.5W 60 KT…EXTRATROPICAL
96HR VT 31/1200Z 50.0N 53.0W 45 KT…EXTRATROPICAL
120HR VT 01/1200Z 52.5N 37.0W 30 KT…EXTRATROPICAL

DATA FROM NOAA BUOY 41047 AND THE AIR FORCE RECONNAISSANCE AIRCRAFT HAVE BEEN CRITICAL IN LOCATING THE BROAD AND ELONGATED CIRCULATION OF DANNY THIS MORNING…WHICH APPEARS TO HAVE MADE ANOTHER NORTHWARD REFORMATION.

THE AIR FORCE PLANE FOUND 55 KT WINDS AT 850 MB AND DROPSONDE AND RELIABLE SFMR WINDS OF ABOUT 45 KT. AN EARLIER NOAA HURRICANE HUNTER AIRCRAFT SHOWED 12000 FT WINDS OF 66 KT AND RELIABLE SFMR VALUES OF 45-50 KT.

THE NOAA SFMR DATA ALSO REASONABLY FIT A 2254 UTC QUIKSCAT PASS WHICH HAD A FEW 50 KT WIND BARBS. THEREFORE…THE ADVISORY INTENSITY IS SET TO 50 KT.

IT SHOULD BE NOTED THAT DANNY DOES NOT HAVE A TYPICAL TROPICAL CYCLONE STRUCTURE AND HAS MOST OF THE STRONG WINDS LOCATED WELL NORTH AND EAST OF THE CENTER.

WITH ALL THE CENTER REFORMATIONS…THE INITIAL MOTION IS JUST ABOUT IMPOSSIBLE TO DETERMINE…BUT THE BEST ESTIMATE IS 315/9.

DESPITE THE INITIAL UNCERTAINTY…THE MODELS ARE IN EXCELLENT AGREEMENT ON A TURN TOWARD THE NORTH ON FRIDAY AS DANNY MOVES BETWEEN A RIDGE OVER THE WESTERN ATLANTIC OCEAN AND A SHORTWAVE TROUGH OVER THE SOUTHEASTERN UNITED STATES.

THE STORM SHOULD THEN ACCELERATE NORTHEASTWARD DUE TO INCREASING FLOW AHEAD OF A LARGER TROUGH OVER THE GREAT LAKES.

THE OFFICIAL FORECAST IS SHIFTED EASTWARD BECAUSE OF THE CENTER REFORMATION AND THE GOOD TRACK MODEL AGREEMENT.

HOWEVER…ANY SIGNIFICANT DEVIATION TO THE WEST OF THE FORECAST TRACK WOULD BRING DANNY CLOSER TO THE U.S. EAST COAST.

WHILE SHEAR IS RELATIVELY LIGHT NEAR DANNY FOR THE TIME BEING…GLOBAL MODELS INCREASE THE SHEAR WITHIN A DAY OR SO.

DESPITE THIS PATTERN CHANGE…ALL OF THE RELIABLE INTENSITY MODELS MAKE DANNY A HURRICANE IN A COUPLE OF DAYS…AND MOST OF THE GLOBAL MODELS SHOW THE SYSTEM INTENSIFYING DESPITE THE SHEAR.

SOME OF THIS INCREASE IN STRENGTH COULD BE DUE TO BAROCLINIC INFLUENCES AS THE GLOBAL MODELS ARE SHOWING A RATHER DIFFLUENT PATTERN NEAR THE TROPICAL CYCLONE WITH STRONG JET DYNAMICS.

HOWEVER…THIS WOULD ARGUE MORE FOR A STRONG EXTRATROPICAL CYCLONE RATHER THAN A TROPICAL CYCLONE.

THE OFFICIAL FORECAST STILL SHOWS THIS SYSTEM TO BE A HURRICANE IN A COUPLE OF DAYS BUT GIVEN THE SEEMINGLY UNFAVORABLE ENVIRONMENT…THE NHC FORECAST IS LOWER THAN MOST OF THE GUIDANCE AND MAKES DANNY EXTRATROPICAL BY 72 HOURS.

HURRICANE DANNY FORECAST POSITIONS AND MAX WINDS

INITIAL 27/0900Z 27.4N 72.1W 50 KT
12HR VT 27/1800Z 28.4N 73.1W 50 KT
24HR VT 28/0600Z 30.0N 74.0W 55 KT
36HR VT 28/1800Z 32.3N 74.0W 60 KT
48HR VT 29/0600Z 35.7N 72.9W 65 KT
72HR VT 30/0600Z 44.0N 66.5W 65 KT…EXTRATROPICAL
96HR VT 31/0600Z 50.0N 55.0W 50 KT…EXTRATROPICAL
120HR VT 01/0600Z 53.0N 40.0W 35 KT…EXTRATROPICAL

INTERESTS IN THE BAHAMAS AND THE SOUTHEASTERN UNITED STATES SHOULD MONITOR THE PROGRESS OF DANNY.

TROPICAL STORM CENTER LOCATED NEAR 25.2N 71.2W AT 26/2100Z
POSITION ACCURATE WITHIN 30 NM

PRESENT MOVEMENT TOWARD THE WEST-NORTHWEST OR 300 DEGREES AT 10 KT

ESTIMATED MINIMUM CENTRAL PRESSURE 1007 MB
MAX SUSTAINED WINDS 40 KT WITH GUSTS TO 50 KT.
34 KT…….150NE 0SE 0SW 120NW.
12 FT SEAS..150NE 75SE 75SW 150NW.
WINDS AND SEAS VARY GREATLY IN EACH QUADRANT. RADII IN NAUTICAL MILES ARE THE LARGEST RADII EXPECTED ANYWHERE IN THAT QUADRANT.

REPEAT…CENTER LOCATED NEAR 25.2N 71.2W AT 26/2100Z
AT 26/1800Z CENTER WAS LOCATED NEAR 25.0N 70.8W

FORECAST VALID 27/0600Z 26.0N 72.5W
MAX WIND 40 KT…GUSTS 50 KT.
34 KT…150NE 0SE 0SW 120NW.

FORECAST VALID 27/1800Z 27.1N 73.8W
MAX WIND 45 KT…GUSTS 55 KT.
34 KT…150NE 90SE 45SW 120NW.

FORECAST VALID 28/0600Z 28.7N 74.5W
MAX WIND 50 KT…GUSTS 60 KT.
50 KT… 30NE 0SE 0SW 0NW.
34 KT…150NE 90SE 60SW 120NW.

FORECAST VALID 28/1800Z 31.1N 74.5W
MAX WIND 60 KT…GUSTS 75 KT.
50 KT… 45NE 45SE 30SW 30NW.
34 KT…150NE 150SE 90SW 90NW.

FORECAST VALID 29/1800Z 38.5N 71.5W
MAX WIND 65 KT…GUSTS 80 KT.
50 KT… 60NE 60SE 45SW 45NW.
34 KT…150NE 150SE 100SW 100NW.

EXTENDED OUTLOOK. NOTE…ERRORS FOR TRACK HAVE AVERAGED NEAR 225 NM ON DAY 4 AND 300 NM ON DAY 5…AND FOR INTENSITY NEAR 20 KT EACH DAY

OUTLOOK VALID 30/1800Z 47.5N 63.5W…EXTRATROPICAL MAX WIND 60 KT…GUSTS 75 KT.

OUTLOOK VALID 31/1800Z 53.1N 48.0W…EXTRATROPICAL MAX WIND 45 KT…GUSTS 55 KT.

REQUEST FOR 3 HOURLY SHIP REPORTS WITHIN 300 MILES OF 25.2N 71.2W

NEXT ADVISORY AT 27/0300Z

$$
FORECASTER BEVEN

SATELLITE IMAGERY SHOWS THAT THE AREA OF DISTURBED WEATHER EAST OF THE BAHAMAS HAS DEVELOPED A WELL-DEFINED LOW-LEVEL CIRCULATION…WITH REPORTS FROM A NOAA HURRICANE HUNTER AIRCRAFT INDICATING THE SYSTEM WAS BEST DEVELOPED BELOW 12000 FT.

QUIKSCAT DATA AND A FEW OBSERVATIONS FROM THE STEPPED FREQUENCY MICROWAVE RADIOMETER SHOW TROPICAL STORM-FORCE WINDS OCCURRING NORTH AND NORTHEAST OF THE CENTER…WHICH IS THE BASIS FOR THE INITIAL INTENSITY OF 40 KT.

THE STORM HAS BEEN TANGLED UP WITH AN UPPER-LEVEL LOW FOR THE PAST 24 HR…AND THE STRUCTURE AS MUCH RESEMBLES A SUBTROPICAL CYCLONE AS A TROPICAL CYCLONE.

HOWEVER…CYCLONE PHASE ANALYSES FROM FLORIDA STATE UNIVERSITY SUGGEST THAT DANNY IS MARGINALLY MORE TROPICAL THAN SUBTROPICAL…HENCE THE DESIGNATION OF TROPICAL STORM.

THE INITIAL MOTION IS A SOMEWHAT UNCERTAIN 295/16.

DANNY IS ON THE NORTH SIDE OF A MID/UPPER-LEVEL LOW CENTERED OVER HISPANIOLA AND SOUTHWEST OF A MID/UPPER-LEVEL RIDGE CENTER EAST OF BERMUDA.

THIS PATTERN SHOULD STEER DANNY GENERALLY NORTHWESTWARD WITH DECELERATION FOR THE NEXT 24-36 HR.

AFTER THAT…THE LARGE SCALE MODELS AGREE THAT A MID/UPPER-LEVEL TROUGH SHOULD DEVELOP OVER THE GREAT LAKES…WITH A MID/UPPER-LEVEL LOW OVER THE GULF COAST STATES MOVING EASTWARD OR NORTHEASTWARD.

THIS EVOLUTION SHOULD CAUSE DANNY TO TURN NORTHWARD AND THEN RECURVE INTO THE WESTERLIES.

WHILE THE MODELS AGREE ON THE SCENARIO…THERE IS ENOUGH SPREAD IN THE TRACK GUIDANCE TO MAKE IT UNCERTAIN WHAT LAND AREA DANNY MAY AFFECT.

THE NAM AND THE CANADIAN MODELS FORECAST DANNY TO MAKE LANDFALL IN EASTERN NORTH CAROLINA IN ABOUT 72 HR AND MOVE UP THE U. S. EASTERN SEABOARD…WHILE THE GFS…HWRF… AND GFDL SHOW A MORE EASTERLY TRACK THAT KEEPS DANNY OFFSHORE UNTIL IT REACHES THE CANADIAN MARITIMES.

THE FORECAST SPLITS THE DIFFERENCE BETWEEN THESE EXTREMES AND IS A LITTLE TO THE LEFT OF THE MODEL CONSENSUS.

THE FORECAST TRACK IS ROUGHLY PARALLEL TO THE U. S. EAST COAST…AND ANY DEVIATION FROM THE TRACK COULD MAKE A LARGE DIFFERENCE IN WHAT AREAS GET IMPACTED BY DANNY.

THEREFORE…IT IS IMPORTANT NOT TO FOCUS TOO MUCH ON THE EXACT FORECAST TRACK.

THE INTENSITY FORECAST IS PROBLEMATIC.

WATER VAPOR IMAGERY SHOWS UPPER-LEVEL LOWS NORTH AND SOUTH OF DANNY CONNECTED BY A CYCLONIC SHEAR AXIS.

THIS IS NOT A IDEAL PATTERN FOR STRENGTHENING…AND THE LARGE-SCALE MODELS SUGGEST IT MAY TAKE 24-36 HR FOR THE ENVIRONMENT TO BECOME MORE FAVORABLE.

BASED ON THIS AND THE CURRENT ORGANIZATION OF THE STORM…THE INTENSITY FORECAST CALLS FOR SLOW STRENGTHENING FOR THE FIRST 36 HR.

IT THEN SHOWS A FASTER STRENGTHENING FROM 36-48 HR AS CONDITIONS BECOME MORE FAVORABLE.

AFTER 48 HR…STRONG UPPER-LEVEL SOUTHWESTERLY WINDS ASSOCIATED WITH THE EASTERN U. S. TROUGHS ARE EXPECTED TO CAUSE INCREASED SHEAR AND THE BEGINNING OF EXTRATROPICAL TRANSITION.

THE INTENSITY FORECAST THUS CALLS FOR DANNY TO REACH 65 KT IN 72 HR…THEN BECOME EXTRATROPICAL BY 96 HR.

THE INTENSITY FORECAST IS IN BEST AGREEMENT WITH THE SHIPS AND LGEM MODELS.

HOWEVER…IT IS WEAKER THAN THE FORECASTS OF THE GFDL AND HWRF.

TROPICAL STORM DANNY FORECAST POSITIONS AND MAX WINDS

INITIAL 26/1500Z 24.9N 70.3W 40 KT
12HR VT 27/0000Z 25.8N 72.0W 40 KT
24HR VT 27/1200Z 26.8N 73.6W 45 KT
36HR VT 28/0000Z 28.1N 74.5W 50 KT
48HR VT 28/1200Z 30.1N 75.2W 60 KT
72HR VT 29/1200Z 36.0N 73.5W 65 KT
96HR VT 30/1200Z 45.0N 67.0W 65 KT…EXTRATROPICAL
120HR VT 31/1200Z 52.0N 53.0W 60 KT…EXTRATROPICAL