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Tropical Storm ERIN Forecast Discussion Number 11

2013-08-17 16:32:58| National Hurricane Center (Atlantic)

Issued at 1100 AM AST SAT AUG 17 2013 000 WTNT45 KNHC 171432 TCDAT5 TROPICAL STORM ERIN DISCUSSION NUMBER 11 NWS NATIONAL HURRICANE CENTER MIAMI FL AL052013 1100 AM AST SAT AUG 17 2013 THE CLOUD PATTERN OF ERIN HAS CHANGED LITTLE DURING THE LAST SEVERAL HOURS. THE LOW-LEVEL CENTER IS EXPOSED TO THE SOUTH OF AN AREA OF DEEP CONVECTION DUE TO STRONG SOUTHERLY FLOW ALOFT. THE INITIAL WIND SPEED IS HELD AT 35 KT...A LITTLE HIGHER THAN THE DVORAK CLASSIFICATIONS. ERIN IS STILL OVER 25-26C WATERS...AND ALTHOUGH THE SSTS INCREASE ALONG THE FORECAST TRACK...THE CONTINUED IMPACT OF DRY STABLE AIR COMBINED WITH EVEN STRONGER SHEAR SHOULD CAUSE THE CYCLONE TO SLOWLY WEAKEN. THE NHC FORECAST SHOWS ERIN DEGENERATING TO A REMNANT LOW BY DAY 4 AND DISSIPATING BY DAY 5...HOWEVER...THIS CERTAINLY COULD OCCUR SOONER AS SHOWN BY AT LEAST A FEW MODELS. VISIBLE SATELLITE IMAGES INDICATE THAT ERIN HAS JOGGED TO THE NORTH DURING THE LAST 6 HOURS. A SMOOTHED INITIAL MOTION ESTIMATE IS 315/10. A TURN TO THE LEFT...OR WEST-NORTHWEST...IS EXPECTED TO BEGIN LATER TODAY AND PERSIST THROUGH MONDAY WHILE A SUBTROPICAL RIDGE BECOMES MORE ESTABLISHED TO THE NORTH OF THE STORM. IF ERIN SURVIVES BEYOND A FEW DAYS...IT WILL LIKELY TURN BACK TO THE NORTHWEST TOWARD ANOTHER WEAKNESS IN THE RIDGE. THE NHC TRACK FORECAST HAS BEEN ADJUSTED NORTHWARD...MAINLY TO ACCOUNT FOR THE INITIAL POSITION. FORECAST POSITIONS AND MAX WINDS INIT 17/1500Z 19.8N 35.7W 35 KT 40 MPH 12H 18/0000Z 20.5N 37.2W 35 KT 40 MPH 24H 18/1200Z 21.1N 39.0W 30 KT 35 MPH 36H 19/0000Z 21.8N 41.0W 30 KT 35 MPH 48H 19/1200Z 22.6N 43.4W 30 KT 35 MPH 72H 20/1200Z 25.0N 47.8W 30 KT 35 MPH 96H 21/1200Z 28.5N 50.0W 25 KT 30 MPH...POST-TROP/REMNT LOW 120H 22/1200Z...DISSIPATED $$ FORECASTER CANGIALOSI

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Tropical Storm ERIN Forecast Discussion Number 10

2013-08-17 10:41:26| National Hurricane Center (Atlantic)

Issued at 500 AM AST SAT AUG 17 2013 000 WTNT45 KNHC 170841 TCDAT5 TROPICAL STORM ERIN DISCUSSION NUMBER 10 NWS NATIONAL HURRICANE CENTER MIAMI FL AL052013 500 AM AST SAT AUG 17 2013 THE CENTER OF ERIN IS AT LEAST PARTLY EXPOSED NEAR THE SOUTHWESTERN EDGE OF THE MAIN CONVECTIVE CLUSTER DUE TO 15 KT OF SOUTHWESTERLY VERTICAL WIND SHEAR...AND THE CONVECTION IS SOMEWHAT FARTHER FROM THE CENTER THAN 6 HOURS AGO. THERE IS NO RECENT DATA FROM NEAR THE CENTER...SO THE INITIAL INTENSITY IS HELD AT 35 KT...WHICH IS ABOVE THE SATELLITE INTENSITY ESTIMATES FROM TAFB AND SAB. THE INITIAL MOTION IS 300/13. THERE IS NO CHANGE TO THE TRACK FORECAST PHILOSOPHY FROM THE PREVIOUS ADVISORY. A GRADUALLY STRENGTHENING SUBTROPICAL RIDGE SHOULD STEER ERIN GENERALLY WEST-NORTHWESTWARD FOR THE NEXT 24-36 HOUR. THIS SHOULD BE FOLLOWED BY A TURN MORE TO THE LEFT AROUND A STRONGER LOW-LEVEL RIDGE THROUGH 72H. THEREAFTER...A TURN BACK TO THE NORTHWEST IS FORECAST WHEN ERIN...OR ITS REMNANTS...MOVES TOWARD A BREAK IN THE RIDGE BETWEEN 50W-60W. THE NEW FORECAST TRACK IS SHIFTED A LITTLE TO THE NORTH OF THE PREVIOUS TRACK IN BEST AGREEMENT WITH THE ECMWF... UKMET...CANADIAN..AND NAVGEM MODELS. THE TRACK LIES WELL TO THE LEFT OF THE GFS...WHICH RECURVES ERIN THROUGH THE BREAK IN THE RIDGE. ERIN IS CURRENTLY OVER SEA SURFACE TEMPERATURES OF 25C-26C. WHILE THE FORECAST TRACK TAKES THE CYCLONE OVER WARMER WATER...THE CYCLONE IS MOVING INTO A VERY DRY MID/UPPER-LEVEL AIR MASS AS SEEN IN WATER VAPOR AND METEOSAT AIR MASS IMAGERY. IN ADDITION...THE SOUTHWESTERLY SHEAR IS EXPECTED TO GRADUALLY INCREASE DURING THE FORECAST PERIOD. THE NEW INTENSITY FORECAST IS THE SAME AS THE PREVIOUS FORECAST IN CALLING FOR ERIN TO WEAKEN TO A DEPRESSION IN ABOUT 36 HOURS AND TO DEGENERATE TO A REMNANT LOW IN ABOUT 96 HOURS. AN ALTERNATIVE SCENARIO IS THAT ERIN DISSIPATES EARLIER THAN CURRENTLY FORECAST...AS SHOWN BY ALL OF THE GLOBAL MODELS EXCEPT THE GFS. FORECAST POSITIONS AND MAX WINDS INIT 17/0900Z 18.9N 35.6W 35 KT 40 MPH 12H 17/1800Z 19.7N 37.1W 35 KT 40 MPH 24H 18/0600Z 20.4N 38.9W 35 KT 40 MPH 36H 18/1800Z 20.9N 40.8W 30 KT 35 MPH 48H 19/0600Z 21.4N 43.1W 30 KT 35 MPH 72H 20/0600Z 23.0N 48.0W 30 KT 35 MPH 96H 21/0600Z 25.5N 52.0W 25 KT 30 MPH...POST-TROP/REMNT LOW 120H 22/0600Z...DISSIPATED $$ FORECASTER BEVEN

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Tropical Storm ERIN Forecast Discussion Number 9

2013-08-17 04:30:55| National Hurricane Center (Atlantic)

Issued at 1100 PM AST FRI AUG 16 2013 000 WTNT45 KNHC 170230 TCDAT5 TROPICAL STORM ERIN DISCUSSION NUMBER 9 NWS NATIONAL HURRICANE CENTER MIAMI FL AL052013 1100 PM AST FRI AUG 16 2013 THUNDERSTORMS HAVE MARKEDLY INCREASED NEAR THE CENTER OF ERIN DURING THE PAST FEW HOURS. THE CENTER APPEARS TO BE ON THE SOUTHWESTERN EDGE OF A LARGE COLD CLOUD SHIELD...WHICH IS CONSISTENT WITH A SOUTHWESTERLY SHEAR ENVIRONMENT. SHIP MGSG6 PASSED NEAR THE CENTER RECENTLY AND REPORTED SUSTAINED WINDS OF 40 KT. A REVIEW OF THE HISTORY OF THE SHIP WIND DATA SUGGESTS THE REPORT IS PROBABLY A FEW KNOTS TOO HIGH...BUT IT EASILY SUPPORTS A 35 KT INITIAL INTENSITY. CONVECTION WILL LIKELY FLUCTUATE DURING THE NEXT DAY OR SO WHILE ERIN MOVES OVER MARGINALLY WARM WATERS AND IN A MODERATE SHEAR ENVIRONMENT. WEAKENING SHOULD OCCUR BY 36H DUE TO AN INCREASE IN SHEAR...WHICH WOULD PROMOTE THE MIXING OF VERY DRY AIR ALOFT INTO THE CENTER OF THE CYCLONE. ALTHOUGH THE SSTS NOTABLY INCREASE IN A FEW DAYS...A COMBINATION OF THE DRY ENVIRONMENT...STRONG SHEAR AND UPPER-LEVEL CONVERGENCE WILL PROBABLY CAUSE ERIN TO DEGENERATE INTO A REMNANT LOW BY 96H. THIS SOLUTION IS CONSISTENT WITH THE RELIABLE GLOBAL MODELS...ALTHOUGH MOST OF THESE MODELS DISSIPATE THE CYCLONE EVEN EARLIER THAN THE NEW NHC FORECAST. ERIN APPEARS TO BE MOVING TO THE NORTHWEST AT ABOUT 14 KT... ALTHOUGH THE CENTER IS HARDER TO LOCATE NOW DUE TO ALL OF THE CONVECTION. A GRADUAL TURN TOWARD THE WEST-NORTHWEST IS EXPECTED AS ERIN ENCOUNTERS A REBUILDING SUBTROPICAL RIDGE. THE CYCLONE SHOULD TURN MORE TO THE LEFT AROUND A STRONGER LOW-LEVEL RIDGE THROUGH 72H. THEREAFTER...A TURN BACK TO THE NORTHWEST IS FORECAST WHEN ERIN...OR ITS REMNANTS...MOVES TOWARD A WEAKNESS IN THE RIDGE. THE NEW NHC FORECAST IS VERY CLOSE TO THE PREVIOUS ONE THROUGH 36H...THEN IS SHIFTED WESTWARD NEAR A CONSENSUS OF THE UKMET... GFS...ECMWF...AND FLORIDA STATE SUPERENSEMBLE GUIDANCE AFTER THAT TIME. FORECAST POSITIONS AND MAX WINDS INIT 17/0300Z 18.5N 34.5W 35 KT 40 MPH 12H 17/1200Z 19.5N 36.1W 35 KT 40 MPH 24H 18/0000Z 20.2N 38.1W 35 KT 40 MPH 36H 18/1200Z 20.7N 39.9W 30 KT 35 MPH 48H 19/0000Z 21.0N 42.2W 30 KT 35 MPH 72H 20/0000Z 22.0N 47.0W 30 KT 35 MPH 96H 21/0000Z 24.5N 51.5W 25 KT 30 MPH...POST-TROP/REMNT LOW 120H 22/0000Z...DISSIPATED $$ FORECASTER BLAKE

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Tropical Depression ERIN Forecast Discussion Number 8

2013-08-16 22:31:17| National Hurricane Center (Atlantic)

Issued at 500 PM AST FRI AUG 16 2013 000 WTNT45 KNHC 162030 TCDAT5 TROPICAL DEPRESSION ERIN DISCUSSION NUMBER 8 NWS NATIONAL HURRICANE CENTER MIAMI FL AL052013 500 PM AST FRI AUG 16 2013 THERE HAS BEEN LITTLE CHANGE IN THE STRUCTURE OF ERIN THROUGHOUT THE DAY. THE CLOUD PATTERN CONSISTS OF A WELL-DEFINED LOW-LEVEL SWIRL WITH SMALL PATCHES OF CONVECTION. SINCE THE SATELLITE APPEARANCE OF THE CYCLONE HAS NOT CHANGED MUCH...THE INITIAL INTENSITY IS HELD AT 30 KT. THE DEPRESSION CURRENTLY LIES OVER 25-26C WATERS AND IS EMBEDDED WITHIN A FAIRLY STABLE AIRMASS. EVEN THOUGH ERIN WILL BE MOVING OVER WARMER WATERS IN A COUPLE OF DAYS...WEST-SOUTHWESTERLY WIND SHEAR IS EXPECTED TO INCREASE WHILE THE SYSTEM REMAINS IN A STABLE ATMOSPHERE. THE NHC WIND SPEED FORECAST IS THE SAME AS BEFORE...AND KEEPS ERIN STEADY STATE THROUGHOUT THE FORECAST PERIOD. AS MENTIONED IN PREVIOUS DISCUSSIONS...ERIN COULD DEGENERATE TO A REMNANT LOW OR AN OPEN TROUGH DURING THE NEXT FEW DAYS...AS SHOWN BY SOME OF THE DYNAMICAL MODELS. ERIN REMAINS ON TRACK...AND IS STILL MOVING WEST-NORTHWESTWARD AT ABOUT 15 KT. A SLIGHTLY SLOWER MOTION TOWARD THE WEST-NORTHWEST OR NORTHWEST IS FORECAST THROUGH SATURDAY WHILE THE DEPRESSION FEELS SOME INFLUENCE FROM A WEAKNESS IN THE SUBTROPICAL RIDGE. A SLIGHT BEND TO THE LEFT IS PREDICTED ON SUNDAY AND MONDAY WHEN ERIN LIES ON THE SOUTH SIDE OF THE RIDGE AXIS. THEREAFTER...A TURN BACK TO THE NORTHWEST IS FORECAST AS ERIN...OR ITS REMNANTS...MOVES TOWARD ANOTHER WEAKNESS IN THE RIDGE. THE NHC TRACK FORECAST IS NUDGED NORTHWARD FOR THIS ADVISORY TO COME INTO BETTER AGREEMENT WITH THE LATEST GUIDANCE. FORECAST POSITIONS AND MAX WINDS INIT 16/2100Z 17.7N 33.3W 30 KT 35 MPH 12H 17/0600Z 18.8N 35.0W 30 KT 35 MPH 24H 17/1800Z 19.8N 37.1W 30 KT 35 MPH 36H 18/0600Z 20.4N 39.0W 30 KT 35 MPH 48H 18/1800Z 20.9N 41.0W 30 KT 35 MPH 72H 19/1800Z 22.7N 45.8W 30 KT 35 MPH 96H 20/1800Z 25.0N 50.5W 30 KT 35 MPH 120H 21/1800Z 28.0N 53.5W 30 KT 35 MPH $$ FORECASTER CANGIALOSI

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Tropical Depression ERIN Forecast Discussion Number 7

2013-08-16 16:32:56| National Hurricane Center (Atlantic)

Issued at 1100 AM AST FRI AUG 16 2013 000 WTNT45 KNHC 161432 TCDAT5 TROPICAL DEPRESSION ERIN DISCUSSION NUMBER 7 NWS NATIONAL HURRICANE CENTER MIAMI FL AL052013 1100 AM AST FRI AUG 16 2013 SATELLITE IMAGES INDICATE THAT ERIN HAS WEAKENED. THE STRUCTURE OF THE CYCLONE CONSISTS OF A LOW-LEVEL CLOUD SWIRL WITH A COUPLE OF SMALL AREAS OF CONVECTION SOUTH AND EAST OF THE CENTER. THE DVORAK CLASSIFICATIONS HAVE FALLEN...AND ERIN IS DOWNGRADED TO A 30-KT TROPICAL DEPRESSION FOR THIS ADVISORY. THE OBSERVED WEAKENING IS LIKELY THE RESULT OF COOL SEA SURFACE TEMPERATURES AND STABLE AIR... AS SEEN IN THE GOES-R PROVING GROUND AIRMASS PRODUCT. ALTHOUGH ERIN IS EXPECTED TO MOVE OVER WARMER WATER IN A FEW DAYS... SOUTHWESTERLY SHEAR IS ANTICIPATED TO INCREASE WHILE THE DEPRESSION REMAINS IN A STABLE ATMOSPHERE. THE NHC INTENSITY PREDICTION CALLS FOR LITTLE CHANGE IN STRENGTH THROUGHOUT THE FORECAST PERIOD. IT IS POSSIBLE THAT ERIN COULD DEGENERATE TO A REMNANT LOW OR AN OPEN TROUGH DURING THE NEXT FEW DAYS...AS SUGGESTED BY SOME OF THE MODEL GUIDANCE. THE DEPRESSION IS MOVING WEST-NORTHWESTWARD AT ABOUT 15 KT. THIS GENERAL MOTION WITH SOME DECREASE IN FORWARD IS EXPECTED DURING THE NEXT 36 HOURS WHILE THE CYCLONE FEELS SOME INFLUENCE FROM A WEAKNESS IN THE SUBTROPICAL RIDGE. BETWEEN 36 AND 72 HOURS...LOW- TO MID-LEVEL RIDGING IS FORECAST TO BECOME MORE PRONOUNCED TO THE NORTH OF THE SYSTEM...CAUSING A TURN TOWARD THE WEST. BEYOND THAT TIME...A GRADUAL TURN TO THE NORTHWEST IS PREDICTED WHEN THE WEAK CYCLONE MOVES TOWARD ANOTHER WEAKNESS IN THE RIDGE. THE NHC TRACK FORECAST IS VERY SIMILAR TO THE PREVIOUS ONE AND CLOSE TO THE MULTI-MODEL CONSENSUS TVCA. FORECAST POSITIONS AND MAX WINDS INIT 16/1500Z 16.9N 32.1W 30 KT 35 MPH 12H 17/0000Z 17.9N 34.0W 30 KT 35 MPH 24H 17/1200Z 19.1N 36.2W 30 KT 35 MPH 36H 18/0000Z 19.9N 38.2W 30 KT 35 MPH 48H 18/1200Z 20.2N 40.2W 30 KT 35 MPH 72H 19/1200Z 21.1N 44.6W 30 KT 35 MPH 96H 20/1200Z 23.5N 49.5W 30 KT 35 MPH 120H 21/1200Z 25.5N 52.5W 30 KT 35 MPH $$ FORECASTER CANGIALOSI

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