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Tropical Storm ERIN Forecast Discussion Number 6

2013-08-16 10:32:19| National Hurricane Center (Atlantic)

Issued at 500 AM AST FRI AUG 16 2013 000 WTNT45 KNHC 160832 TCDAT5 TROPICAL STORM ERIN DISCUSSION NUMBER 6 NWS NATIONAL HURRICANE CENTER MIAMI FL AL052013 500 AM AST FRI AUG 16 2013 ERIN REMAINS DISORGANIZED THIS MORNING...WITH THE LOW-LEVEL CENTER PARTLY EXPOSED TO THE NORTHWEST OF THE MAIN CONVECTIVE CLUSTER. SATELLITE INTENSITY ESTIMATES ARE 35 KT FROM TAFB AND 30 KT FROM SAB...AND A CIMSS AMSU ESTIMATE NEAT 0400 UTC WAS 31 KT. THE INITIAL INTENSITY REMAINS 35 KT FOR THIS ADVISORY. THE INITIAL MOTION IS 295/14. ERIN IS CURRENTLY BEING STEERED BY A LOW/MID-LEVEL RIDGE TO THE NORTH AND NORTHEAST. THE GLOBAL MODELS FORECAST THIS RIDGE TO STRENGTHEN DURING THE NEXT 2-3 DAYS AS MID/UPPER-LEVEL LOW SOUTH OF THE AZORES MOVES OFF TO THE NORTHEAST. THE TRACK GUIDANCE IS IN FAIRLY GOOD AGREEMENT THAT ERIN WILL CONTINUE WEST-NORTHWESTWARD FOR 36-48 HR...THEN TURN MORE WESTWARD AS THE CYCLONE BECOME SHALLOWER AND STEERED MORE BY THE LOW-LEVEL FLOW. SUBSEQUENTLY...THE GFS...UKMET...CANADIAN...AND NAVGEM MODELS FORECAST A SECOND WEAKNESS TO DEVELOP IN THE RIDGE BETWEEN 50W-60W BY 120 HOURS...WHICH WOULD ALLOW ERIN TO TURN MORE NORTHWARD. THE TRACK GUIDANCE ENVELOPE HAS AGAIN SHIFTED TO THE NORTH...AND THE NEW TRACK FORECAST IS LIKEWISE SHIFTED NORTH OF THE PREVIOUS FORECAST. HOWEVER...THE NEW TRACK IS STILL SOUTH OF THE MODEL CONSENSUS. WHILE ERIN IS CURRENTLY IN A LIGHT VERTICAL WIND SHEAR ENVIRONMENT...THE CYCLONE IS CURRENTLY OVER SEA SURFACE TEMPERATURES OF 25C-26C...AND METEOSAT AIRMASS IMAGERY SUGGESTS THE CYCLONE IS APPROACHING AN AREA OF DRIER AIR. THE INTENSITY GUIDANCE NOW FORECASTS SHORT-TERM INTENSIFICATION THAN 6 HOURS AGO...AND THUS THE NEW INTENSITY FORECAST IS REDUCED FROM THAT OF THE PREVIOUS ADVISORY. IN THE LONG TERM...AFTER 72 HOURS...ERIN IS FORECAST TO REACH INCREASING SEA SURFACE TEMPERATURES. HOWEVER... IT IS ALSO EXPECTED TO ENCOUNTER INCREASING SOUTHWESTERLY SHEAR AND MORE DRY AIR. THE INTENSITY FORECAST IS THE SAME AS THE PREVIOUS FORECAST IN SHOWING WEAKENING DURING THIS TIME. AN ALTERNATIVE FORECAST SCENARIO IS THAT ERIN DEGENERATES TO A TROPICAL WAVE BEFORE 120 HOURS...AS FORECAST BY ALL OF THE GLOBAL MODELS EXCEPT THE GFS. FORECAST POSITIONS AND MAX WINDS INIT 16/0900Z 16.3N 30.5W 35 KT 40 MPH 12H 16/1800Z 17.3N 32.4W 35 KT 40 MPH 24H 17/0600Z 18.6N 34.7W 40 KT 45 MPH 36H 17/1800Z 19.6N 36.7W 40 KT 45 MPH 48H 18/0600Z 20.3N 38.7W 40 KT 45 MPH 72H 19/0600Z 21.0N 43.0W 40 KT 45 MPH 96H 20/0600Z 22.5N 47.5W 35 KT 40 MPH 120H 21/0600Z 24.5N 51.0W 30 KT 35 MPH $$ FORECASTER BEVEN

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Tropical Storm ERIN Forecast Discussion Number 5

2013-08-16 04:45:19| National Hurricane Center (Atlantic)

Issued at 1100 PM AST THU AUG 15 2013 000 WTNT45 KNHC 160245 TCDAT5 TROPICAL STORM ERIN DISCUSSION NUMBER 5 NWS NATIONAL HURRICANE CENTER MIAMI FL AL052013 1100 PM AST THU AUG 15 2013 CONVECTION ASSOCIATED WITH ERIN HAS BEEN ON THE WANE DURING MOST OF THE EVENING HOURS...ALTHOUGH RECENTLY A SMALL BURST HAS FORMED EAST OF THE CENTER. MICROWAVE PASSES SUGGEST THE SYSTEM IS NOT WELL ORGANIZED...WITH THE LOW-LEVEL CENTER APPARENTLY WEST OF THE MID- LEVEL CENTER. THE INITIAL INTENSITY IS BEING HELD AT 35 KT IN AGREEMENT WITH THE DVORAK ESTIMATE FROM TAFB. THE OVERALL ENVIRONMENT FOR THE NEXT DAY OR TWO SEEMS TO BE CONDUCIVE FOR SOME STRENGTHENING WITH THE SHEAR FORECAST TO BE LIGHT BUT A LIMITING FACTOR OF MARGINAL SSTS. IN A FEW DAYS...ALTHOUGH SSTS ARE FORECAST TO INCREASE...THE GLOBAL MODELS SHOW AN INCREASE IN SHEAR...WHICH WOULD FACILITATE RATHER DRY AIR ALOFT ENTRAINING INTO THE CENTRAL CORE OF ERIN. THUS...THE OFFICIAL NHC FORECAST SHOWS WEAKENING AFTER DAY 3...WHICH IS CONSISTENT WITH THE PREVIOUS FORECAST AND THE FLORIDA STATE SUPERENSEMBLE. MICROWAVE FIXES GIVE AN INITIAL MOTION OF 295/13. THIS GENERAL COURSE IS EXPECTED FOR THE NEXT COUPLE OF DAYS WHILE A MID-LEVEL RIDGE REMAINS TO THE NORTHEAST OF THE TROPICAL CYCLONE. AFTER THAT TIME...THE BIGGEST UNCERTAINTY IS WHETHER A WEAKNESS IN THE RIDGE FROM A MID- TO UPPER-LEVEL LOW LOCATED OVER THE EASTERN ATLANTIC WILL ALLOW THAT TRACK TO CONTINUE. IF THE STORM IS SHALLOW ENOUGH...IT WILL PROBABLY MISS THE WEAKNESS AND INSTEAD TAKE A MORE WESTWARD TURN BECAUSE OF A STRONGER LOW-LEVEL RIDGE. ALTHOUGH THE NEW NHC FORECAST IS SHIFTED NORTHWARD TO COME INTO BETTER AGREEMENT WITH THE SOUTHERN SIDE OF THE GUIDANCE ENVELOPE...IT IS STILL WELL TO THE SOUTH OF THE DYNAMICAL MODEL CONSENSUS. FURTHER ADJUSTMENTS COULD STILL BE NECESSARY IF THIS NORTHWARD TREND IN THE GUIDANCE PERSISTS IN FUTURE CYCLES. FORECAST POSITIONS AND MAX WINDS INIT 16/0300Z 15.5N 29.1W 35 KT 40 MPH 12H 16/1200Z 16.3N 31.1W 35 KT 40 MPH 24H 17/0000Z 17.5N 33.4W 40 KT 45 MPH 36H 17/1200Z 18.6N 35.5W 45 KT 50 MPH 48H 18/0000Z 19.6N 37.4W 45 KT 50 MPH 72H 19/0000Z 20.5N 41.5W 45 KT 50 MPH 96H 20/0000Z 21.5N 46.0W 35 KT 40 MPH 120H 21/0000Z 22.5N 50.0W 30 KT 35 MPH $$ FORECASTER BLAKE

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Tropical Storm ERIN Forecast Discussion Number 4

2013-08-15 22:32:16| National Hurricane Center (Atlantic)

Issued at 500 PM AST THU AUG 15 2013 000 WTNT45 KNHC 152032 TCDAT5 TROPICAL STORM ERIN DISCUSSION NUMBER 4 NWS NATIONAL HURRICANE CENTER MIAMI FL AL052013 500 PM AST THU AUG 15 2013 THE CONVECTIVE PATTERN OF ERIN HAS EVOLVED INTO ONE THAT FEATURES MORE BANDING AWAY FROM THE CENTER AND WARMER CLOUD TOPS NEAR THE CENTER ITSELF. THE INITIAL INTENSITY REMAINS 35 KT BASED ON THE LATEST TAFB DVORAK ESTIMATE. THE INTENSITY FORECAST REASONING REMAINS UNCHANGED. FOR THE NEXT COUPLE OF DAYS...THE CYCLONE WILL BE MOVING THROUGH A MOIST LOW-SHEAR ENVIRONMENT WITH SSTS OF 26-27C...WHICH SHOULD SUPPORT MODEST STRENGTHENING. LATER IN THE PERIOD...ALTHOUGH SSTS INCREASE...ERIN WILL BE MOVING INTO A DRIER MORE STABLE ATMOSPHERE...AND WEAKENING IS EXPECTED. THE NHC INTENSITY FORECAST IS SIMILAR TO THE PREVIOUS ONE AND IS CLOSE TO THE INTENSITY CONSENSUS THROUGH 72 HOURS AND THEN FOLLOWS THE TREND OF THE DYNAMICAL MODELS...SHOWING GRADUAL WEAKENING. THE INITIAL MOTION ESTIMATE IS 290/12...AS THE CYCLONE APPEARS TO HAVE TURNED A BIT TO THE RIGHT DURING THE PAST FEW HOURS. THERE HAS BEEN A SIZEABLE NORTHWARD SHIFT IN NEARLY ALL OF THE TRACK MODEL GUIDANCE THIS CYCLE. THE GLOBAL MODELS NOW SHOW A DEEPER REPRESENTATION OF ERIN MOVING MORE INTO A WEAKNESS IN THE SUBTROPICAL RIDGE TO THE SOUTH OF A MID/UPPER-LEVEL LOW THAT WILL BE MEANDERING SOUTH OF THE AZORES. AS A RESULT...THE MODELS SHOW ERIN GAINING MORE LATITUDE DURING THE FIRST 72 HOURS OR SO. AFTER THAT...A TURN BACK TOWARD THE LEFT IS SHOWN BY MOST OF THE MODELS AS THE CYCLONE WEAKENS. FOR THIS CYCLE A NORTHWARD ADJUSTMENT HAS BEEN MADE TO THE NHC FORECAST...BUT THE NHC TRACK IS ON THE SOUTHERN SIDE OF THE GUIDANCE ENVELOPE...ESPECIALLY AT DAYS 3 THROUGH 5. FURTHER ADJUSTMENTS WILL LIKELY BE NECESSARY IF THIS NORTHWARD TREND IN THE GUIDANCE PERSISTS IN FUTURE CYCLES. FORECAST POSITIONS AND MAX WINDS INIT 15/2100Z 15.0N 27.5W 35 KT 40 MPH 12H 16/0600Z 15.6N 29.6W 40 KT 45 MPH 24H 16/1800Z 16.7N 32.0W 45 KT 50 MPH 36H 17/0600Z 17.5N 34.2W 45 KT 50 MPH 48H 17/1800Z 18.3N 36.3W 50 KT 60 MPH 72H 18/1800Z 19.0N 40.5W 50 KT 60 MPH 96H 19/1800Z 19.5N 44.5W 45 KT 50 MPH 120H 20/1800Z 20.0N 49.0W 35 KT 40 MPH $$ FORECASTER BRENNAN

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Tropical Storm ERIN Forecast Discussion Number 3

2013-08-15 16:40:44| National Hurricane Center (Atlantic)

Issued at 1100 AM AST THU AUG 15 2013 000 WTNT45 KNHC 151440 TCDAT5 TROPICAL STORM ERIN DISCUSSION NUMBER 3 NWS NATIONAL HURRICANE CENTER MIAMI FL AL052013 1100 AM AST THU AUG 15 2013 THE SATELLITE PRESENTATION OF THE CYCLONE HAS CONTINUED TO IMPROVE OVER THE PAST FEW HOURS. INFRARED IMAGERY SHOWS VERY COLD CLOUD TOPS SITUATED NEAR AND TO THE SOUTH OF THE ESTIMATED CENTER POSITION...WITH A SMALL BANDING FEATURE EXTENDING TO THE SOUTHWEST. THE INITIAL INTENSITY OF 35 KT IS SUPPORTED BY A BLEND OF THE LATEST OBJECTIVE AND SUBJECTIVE DVORAK ESTIMATES AND A 1102 UTC ASCAT-A PASS THAT SHOWED WINDS OF 32 KT. ERIN IS EXPECTED TO BE IN AN ENVIRONMENT THAT SUPPORTS SOME STRENGTHENING DURING THE NEXT COUPLE OF DAYS WITH SSTS OF 26-27C...LOW SHEAR...AND A MOIST ENVIRONMENT. BY DAY 3...THE SYSTEM WILL BE MOVING INTO A DRIER AND MORE STABLE ATMOSPHERIC ENVIRONMENT...WHICH SHOULD RESULT IN WEAKENING. THE GLOBAL MODELS AND THE HWRF SHOW A WEAK OR DISSIPATING SYSTEM BY DAY 5...HOWEVER THE SHIPS AND LGEM SHOW LITTLE CHANGE IN INTENSITY OR EVEN STRENGTHENING. THE OFFICIAL FORECAST LEANS A LITTLE TOWARD THE WEAKER SOLUTION AT DAYS 4 AND 5. THE AFOREMENTIONED ASCAT PASS WAS ALSO HELPFUL IN LOCATING THE CENTER OF ERIN...WHICH IS A LITTLE SOUTH AND WEST OF PREVIOUS ESTIMATES. BASED ON A SOUTHWESTWARD ADJUSTMENT OF THE CENTER POSITION THE INITIAL MOTION ESTIMATE IS 285/13. ERIN IS CURRENTLY BEING STEERED BY A NARROW SUBTROPICAL RIDGE TO ITS NORTH...AND THE GUIDANCE IS IN GOOD AGREEMENT ON THIS MOTION CONTINUING FOR THE NEXT COUPLE OF DAYS. BY DAY 3...THE SPREAD IN THE GUIDANCE INCREASES. ON THE RIGHT SIDE OF THE GUIDANCE ENVELOPE THE GFDL... GFDL ENSEMBLE MEAN...ECMWF AND UKMET SHOW A NORTHWESTWARD OR WEST-NORTHWESTWARD MOTION. THE FIM...GFS...GFS ENSEMBLE MEAN AND HWRF ALL SHOW A WESTWARD TRACK...CONSISTENT WITH A SHALLOWER SYSTEM BEING STEERED BY THE LOW-LEVEL FLOW. THE NHC FORECAST AT DAYS 3 THROUGH 5 CONTINUES TO FOLLOW THIS SOUTHERN CAMP OF MODELS AND IS LARGELY AN UPDATE OF THE PREVIOUS NHC TRACK. FORECAST POSITIONS AND MAX WINDS INIT 15/1500Z 14.4N 26.5W 35 KT 40 MPH 12H 16/0000Z 15.0N 28.6W 40 KT 45 MPH 24H 16/1200Z 15.7N 31.2W 45 KT 50 MPH 36H 17/0000Z 16.7N 33.5W 45 KT 50 MPH 48H 17/1200Z 17.4N 35.8W 50 KT 60 MPH 72H 18/1200Z 18.0N 40.0W 50 KT 60 MPH 96H 19/1200Z 18.0N 44.5W 45 KT 50 MPH 120H 20/1200Z 18.0N 49.0W 35 KT 40 MPH $$ FORECASTER BRENNAN

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Tropical Depression FIVE Forecast Discussion Number 2

2013-08-15 10:45:51| National Hurricane Center (Atlantic)

Issued at 500 AM AST THU AUG 15 2013 000 WTNT45 KNHC 150845 TCDAT5 TROPICAL DEPRESSION FIVE DISCUSSION NUMBER 2 NWS NATIONAL HURRICANE CENTER MIAMI FL AL052013 500 AM AST THU AUG 15 2013 SATELLITE IMAGERY THIS MORNING SUGGESTS THAT TROPICAL DEPRESSION FIVE IS GETTING BETTER ORGANIZED. A CONVECTIVE CLUSTER WITH TOPS COLDER THAN -80C HAS FORMED NEAR AND TO THE WEST OF THE CENTER...AND THERE IS OUTER BANDING IN THE SOUTHEASTERN SEMICIRCLE. SATELLITE INTENSITY ESTIMATES FROM TAFB AND SAB ARE BELOW TROPICAL STORM STRENGTH...SO THE CYCLONE WILL REMAIN A 30-KT DEPRESSION FOR THIS ADVISORY. HOWEVER...THIS INTENSITY COULD BE A LITTLE CONSERVATIVE. THE INITIAL MOTION IS 290/14. THE DEPRESSION IS CURRENTLY ON THE SOUTH SIDE OF A LOW/MID-LEVEL RIDGE OVER THE EASTERN ATLANTIC...AND THE TRACK GUIDANCE IS IN GOOD AGREEMENT THAT THIS WILL STEER THE CYCLONE WEST-NORTHWESTWARD FOR THE NEXT 2-3 DAYS. AFTER THAT...THE GUIDANCE DIVERGES. THE GFS...THE GFS ENSEMBLE MEAN...AND THE CANADIAN MODELS SHOW THE SYSTEM TURNING WESTWARD. THE ECMWF...THE UKMET...AND THE GFDL SHOW A WEST-NORTHWESTWARD TO NORTHWESTWARD MOTION...WITH THE CYCLONE MOVING TOWARD A WEAKNESS IN THE RIDGE OVER THE CENTRAL ATLANTIC. OVERALL...THE GUIDANCE ENVELOPE HAS SHOWN A NORTHWARD SHIFT SINCE THE LAST ADVISORY. SINCE THE CYCLONE IS EXPECTED TO WEAKEN AND BE STEERED BY THE LOW-LEVEL FLOW DURING THIS TIME...THE NEW FORECAST TRACK SHOWS A WESTWARD TURN IN BEST AGREEMENT WITH THE GFS. WHILE THE NEW FORECAST TRACK IS A LITTLE NORTH OF THE PREVIOUS TRACK AFTER 48 HR...IT IS WELL TO THE SOUTH OF THE ECMWF...THE UKMET...THE GFDL...AND THE CONSENSUS MODELS. THE DEPRESSION IS CURRENTLY IN AN ENVIRONMENT OF WARM SEA SURFACE TEMPERATURES AND LIGHT VERTICAL WIND SHEAR. THIS SHOULD ALLOW SOME STRENGTHENING UNTIL THE SYSTEM REACHES COOLER WATERS IN 48 HR OR SO. WHILE THE CYCLONE IS FORECAST TO LEAVE THE COOLER WATERS AFTER THAT TIME...THE GFS...ECMWF...AND UKMET ARE IN GOOD AGREEMENT THAT IT SHOULD ENCOUNTER VERY DRY AIR AND WEAKEN...WITH THESE MODELS SHOWING THE SYSTEM DEGENERATING TO A TROPICAL WAVE BY 120 HR. THE NEW INTENSITY FORECAST DOES NOT YET FOLLOW THAT SCENARIO...AS THE SHIPS AND LGEM MODELS SHOW A STEADY-STATE OR STRENGTHENING SYSTEM. INSTEAD...THE FORECAST CALLS FOR A SLOW WEAKENING AS A COMPROMISE BETWEEN THESE EXTREMES. FORECAST POSITIONS AND MAX WINDS INIT 15/0900Z 14.4N 25.2W 30 KT 35 MPH 12H 15/1800Z 15.0N 27.2W 35 KT 40 MPH 24H 16/0600Z 15.7N 30.0W 40 KT 45 MPH 36H 16/1800Z 16.4N 32.6W 45 KT 50 MPH 48H 17/0600Z 17.2N 35.0W 50 KT 60 MPH 72H 18/0600Z 18.0N 39.5W 50 KT 60 MPH 96H 19/0600Z 18.0N 43.5W 45 KT 50 MPH 120H 20/0600Z 18.0N 48.5W 40 KT 45 MPH $$ FORECASTER BEVEN

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