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Tropical Storm DORIAN Forecast Discussion Number 7

2013-07-25 22:51:40| National Hurricane Center (Atlantic)

Issued at 500 PM AST THU JUL 25 2013 000 WTNT44 KNHC 252051 TCDAT4 TROPICAL STORM DORIAN DISCUSSION NUMBER 7 NWS NATIONAL HURRICANE CENTER MIAMI FL AL042013 500 PM AST THU JUL 25 2013 AFTER A BRIEF DISRUPTION IN THE INNER CORE CONVECTIVE PATTERN EARLIER THIS AFTERNOON...DORIAN HAS MADE A COMEBACK WITH A BURST OF COLD-TOPPED CONVECTION DEVELOPING OVER THE PREVIOUSLY EXPOSED LOW-LEVEL CENTER. IN ADDITION...A 1728Z TRMM OVERPASS INDICATED A NEARLY CLOSED LOW-LEVEL EYE HAD DEVELOPED BENEATH A WEAK MID-LEVEL EYE FEATURE. SATELLITE CURRENT INTENSITY ESTIMATES REMAIN AT 55 KT AND 45 KT FROM TAFB AND SAB...RESPECTIVELY...AND AN EARLIER ASCAT-B OVERPASS AT 1230Z INDICATED SURFACE WINDS OF AT LEAST 48 KT NORTH OF THE CENTER. BASED ON THESE DATA...THE INITIAL INTENSITY REMAINS 50 KT FOR THIS ADVISORY. THE INITIAL MOTION ESTIMATE IS 290/16. SEVERAL OF THE MORE RELIABLE MODELS...SUCH AS THE GFS RUN OFF THE NEW WCOSS SUPERCOMPUTER...MADE A SIGNIFICANT SOUTHWARD SHIFT ON THE 12Z MODEL CYCLE. HOWEVER...THE OVERALL GUIDANCE ENVELOPE DID NOT SHIFT SOUTHWARD...BUT RATHER CONVERGED EVEN MORE TIGHTLY AROUND THE PREVIOUS NHC FORECAST TRACKS. AS A RESULT...ESSENTIALLY NO CHANGES WERE MADE TO THE PREVIOUS FORECAST TRACK OR REASONING. AS MENTIONED IN PREVIOUS DISCUSSIONS...THE MAIN DIFFERENCE BETWEEN THE MODELS CONTINUES TO BE THE FORWARD SPEED OF DORIAN. THE ECMWF IS ONE OF THE FASTER MODELS SINCE IT WEAKENS DORIAN ALMOST IMMEDIATELY AND MOVES IT QUICKLY IN THE BRISK EASTERLY TRADE WIND FLOW...WHEREAS THE UKMET AND HWRF MODELS MAINTAIN A VERTICALLY DEEPER AND MORE ROBUST TROPICAL CYCLONE... WHICH MOVES SLOWER IN THE DEEP-LAYER STEERING FLOW. GIVEN THAT THE GFS-ENSEMBLE MEAN...HWRF...AND UKMET MODELS HAVE HANDLED THE INTENSITY AND TRACK OF DORIAN THE BEST THUS FAR...THE OFFICIAL FORECAST LEANS CLOSER TO THOSE SOLUTIONS. THE NEW ADVISORY TRACK IS JUST AN UPDATE OF THE PREVIOUS FORECAST...AND IS IDENTICAL TO BUT REMAINS A LITTLE SLOWER THAN THE CONSENSUS TRACK MODEL TVCN. AFTER SURVIVING THE DIURNAL CONVECTIVE MINIMUM PERIOD...DORIAN IS NOW MOVING OVER 26C SSTS AND TOWARD EVEN WARMER WATERS...AND ALSO INTO THE CONVECTIVE MAXIMUM PERIOD. DORIAN IS FORECAST TO REMAIN IN A LOW SHEAR ENVIRONMENT FOR ANOTHER 72-96 HOURS...DURING WHICH TIME AT LEAST SOME GRADUAL STRENGTHENING IS EXPECTED AS THE CYCLONE MOVES OVER SSTS ABOVE 27C. BY DAY 5...THE UPPER-LEVEL FLOW PATTERN IS QUITE UNCERTAIN WITH DORIAN POSSIBLY MOVING INTO SOME MODERATE TO STRONG SOUTHWESTERLY SHEAR CONDITIONS ACCORDING TO THE GFS AND ECMWF MODELS. GIVEN THIS...THE OFFICIAL FORECAST ONLY SHOWS MODEST STRENGTHENING AND MAINLY FOLLOWS THE LGEM...SHIPS...AND HWRF MODELS. FORECAST POSITIONS AND MAX WINDS INIT 25/2100Z 16.5N 37.8W 50 KT 60 MPH 12H 26/0600Z 17.2N 40.5W 50 KT 60 MPH 24H 26/1800Z 17.8N 44.4W 50 KT 60 MPH 36H 27/0600Z 18.5N 48.6W 55 KT 65 MPH 48H 27/1800Z 19.2N 52.5W 55 KT 65 MPH 72H 28/1800Z 20.4N 59.8W 55 KT 65 MPH 96H 29/1800Z 21.1N 65.2W 60 KT 70 MPH 120H 30/1800Z 21.9N 70.0W 60 KT 70 MPH $$ FORECASTER STEWART

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Tropical Storm FLOSSIE Forecast Discussion Number 4

2013-07-25 22:42:33| National Hurricane Center (East Pacific)

Issued at 200 PM PDT THU JUL 25 2013 000 WTPZ41 KNHC 252041 TCDEP1 TROPICAL STORM FLOSSIE DISCUSSION NUMBER 4 NWS NATIONAL HURRICANE CENTER MIAMI FL EP062013 200 PM PDT THU JUL 25 2013 ALTHOUGH THE CENTER AND THE CIRCULATION ASSOCIATED WITH FLOSSIE APPEAR TO BE BETTER DEFINED...THE CONVECTION HAS WEAKENED DURING THE PAST SEVERAL HOURS. NONETHELESS...1736 UTC ASCAT DATA INDICATE THAT THE CYCLONE HAS MAXIMUM WINDS NEAR 40 KT...AND THAT WILL BE THE ADVISORY INTENSITY. FLOSSIE IS RUNNING OUT OF TIME FOR MUCH MORE STRENGTHENING SINCE THE CIRCULATION WILL BEGIN TO REACH COOLER WATERS IN ABOUT A DAY. THEREFORE...LITTLE CHANGE IN THE WINDS IS SHOWN IN THE FORECAST FOLLOWING THE INTENSITY MODEL CONSENSUS. BY DAY 5...IF NOT SOONER...THE CYCLONE SHOULD HAVE DEGENERATED INTO A REMNANT LOW OR A TROUGH. MICROWAVE AND VISIBLE IMAGES INDICATE THAT FLOSSIE HAS BEEN MOVING WESTWARD OR 270 DEGREES AT 16 KNOTS. IT APPEARS THAT BECAUSE FLOSSIE IS A RELATIVELY SHALLOW CYCLONE...IT IS BEING STEERED WESTWARD BY THE LOW-LEVEL FLOW. THERE IS A STRONG AND PERSISTENT SUBTROPICAL RIDGE TO THE NORTH WHICH WILL KEEP FLOSSIE ON A GENERAL WESTWARD OR WEST-NORTHWESTWARD TRACK THROUGH THE FORECAST PERIOD. THE OFFICIAL FORECAST WAS ADJUSTED SLIGHTLY SOUTHWARD IN AGREEMENT WITH THE SLIGHT SHIFT OBSERVED IN THE TRACK GUIDANCE. FORECAST POSITIONS AND MAX WINDS INIT 25/2100Z 15.3N 127.4W 40 KT 45 MPH 12H 26/0600Z 15.5N 130.0W 40 KT 45 MPH 24H 26/1800Z 16.0N 133.0W 40 KT 45 MPH 36H 27/0600Z 16.5N 136.5W 35 KT 40 MPH 48H 27/1800Z 17.0N 140.0W 35 KT 40 MPH 72H 28/1800Z 18.5N 145.0W 30 KT 35 MPH 96H 29/1800Z 18.5N 150.0W 30 KT 35 MPH 120H 30/1800Z 18.5N 155.0W 25 KT 30 MPH...POST-TROP/REMNT LOW $$ FORECASTER AVILA/BERG

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Tropical Storm FLOSSIE Forecast Discussion Number 2

2013-07-25 10:38:25| National Hurricane Center (East Pacific)

Issued at 200 AM PDT THU JUL 25 2013 000 WTPZ41 KNHC 250838 TCDEP1 TROPICAL STORM FLOSSIE DISCUSSION NUMBER 2 NWS NATIONAL HURRICANE CENTER MIAMI FL EP062013 200 AM PDT THU JUL 25 2013 DEEP CONVECTION ASSOCIATED WITH THE CYCLONE HAS INCREASED IN BOTH COVERAGE AND INTENSITY DURING THE LAST SEVERAL HOURS. ACCORDINGLY...THE LASTEST DVORAK CLASSIFICATIONS HAVE NUDGED UPWARD TO 2.5/35 KT FROM BOTH TAFB AND SAB. IN ADDITION...A RECENT ASCAT PASS SHOWED RELIABLE WINDS AROUND 35 KT. BASED ON THESE DATA...THE DEPRESSION HAS BEEN UPGRADED TO TROPICAL STORM FLOSSIE. CONTINUED SLOW STRENGTHENING SEEMS LIKELY DURING THE NEXT DAY OR SO WHILE THE CYCLONE REMAINS OVER RELATIVELY WARM WATER AND IN A LOW WIND SHEAR ENVIRONMENT. FLOSSIE IS EXPECTED TO MOVE OVER WATERS THAT ARE COOLER THAN 26C ON FRIDAY. THESE LESS FAVORABLE OCEANIC CONDITIONS COMBINED WITH A MORE STABLE AIRMASS AND SOME INCREASE IN WESTERLY SHEAR SHOULD CAUSE THE SYSTEM TO GRADUALLY WEAKEN BEYOND 36 HOURS. THE NHC INTENSITY FORECAST IS THE SAME AS THE PREVIOUS ONE AND LIES GENERALLY NEAR THE INTENSITY MODEL CONSENSUS. THE TROPICAL STORM IS MOVING WEST-NORTHWESTWARD AT ABOUT 13 KT ON THE SOUTHWESTERN SIDE OF A MID-LEVEL RIDGE CENTERED OVER THE SOUTHWESTERN UNITED STATES. A GENERAL WESTWARD TO WEST-NORTHWESTWARD HEADING WITH SOME INCREASE IN FORWARD SPEED IS EXPECTED DURING THE NEXT FEW DAYS DUE TO A STRENGTHENING RIDGE TO THE NORTH OF THE TROPICAL CYCLONE. THE LATEST MODEL GUIDANCE HAS SHIFTED A LITTLE TO THE SOUTH AND IS SLIGHTLY FASTER THAN THE PREVIOUS CYCLE. THE NHC TRACK FORECAST FOLLOWS THE TREND OF THE GUIDANCE...BUT IT IS NOT AS FAR SOUTH AS THE MULTI-MODEL CONSENSUS TVCE. FORECAST POSITIONS AND MAX WINDS INIT 25/0900Z 15.5N 123.9W 35 KT 40 MPH 12H 25/1800Z 15.9N 126.2W 40 KT 45 MPH 24H 26/0600Z 16.4N 129.3W 50 KT 60 MPH 36H 26/1800Z 17.3N 132.5W 50 KT 60 MPH 48H 27/0600Z 18.0N 135.4W 45 KT 50 MPH 72H 28/0600Z 19.6N 141.2W 40 KT 45 MPH 96H 29/0600Z 20.5N 146.0W 35 KT 40 MPH 120H 30/0600Z 21.0N 151.0W 30 KT 35 MPH $$ FORECASTER CANGIALOSI

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Tropical Storm DORIAN Forecast Discussion Number 5

2013-07-25 10:37:55| National Hurricane Center (Atlantic)

Issued at 500 AM AST THU JUL 25 2013 000 WTNT44 KNHC 250837 TCDAT4 TROPICAL STORM DORIAN DISCUSSION NUMBER 5 NWS NATIONAL HURRICANE CENTER MIAMI FL AL042013 500 AM AST THU JUL 25 2013 DORIAN HAS BECOME A LITTLE BETTER ORGANIZED THIS MORNING...WITH STRONGER CONVECTION OCCURRING NEAR THE CENTER. A RECENT AMSU OVERPASS SHOWED A MID-LEVEL EYE ASSOCIATED WITH THIS CONVECTION... ALTHOUGH IT WAS UNCLEAR IF THIS FEATURE WAS DIRECTLY OVER THE LOW-LEVEL CENTER. SATELLITE INTENSITY ESTIMATES ARE 55 KT FROM SAB AND 45 KT FROM TAFB...AND A RECENT AMSU-BASED INTENSITY ESTIMATE FROM CIMSS WAS 48 KT. BASED ON THIS THE INITIAL INTENSITY IS INCREASED TO 50 KT. THE INITIAL MOTION IS 290/15. DORIAN IS ON THE SOUTH SIDE OF A DEEP-LAYER RIDGE THAT COVERS THE CENTRAL AND EASTERN ATLANTIC. THIS FEATURE SHOULD STEER THE CYCLONE QUICKLY WEST-NORTHWESTWARD TO WESTWARD FOR THE NEXT 72 HOURS OR SO. AFTER THAT...DORIAN SHOULD APPROACH A WEAKNESS IN THE RIDGE...WHICH SHOULD LEAD TO A WEST-NORTHWESTWARD MOTION AT A DECREASED FORWARD SPEED. THE GUIDANCE ENVELOPE HAS SHIFTED A BIT TO THE NORTH SINCE THE PREVIOUS ADVISORY. BASED ON THIS...THE NEW FORECAST TRACK WILL BE NUDGED A LITTLE TO THE NORTH...BUT IT LIES SOUTH OF THE CENTER OF THE GUIDANCE ENVELOPE AND THE MODEL CONSENSUS. THE INTENSITY FORECAST IS COMPLEX AND OF LOW CONFIDENCE. DORIAN SHOULD MOVE OVER WARMER SEA SURFACE TEMPERATURES DURING THE NEXT 2-3 DAYS...BUT DURING THIS TIME IT ALSO MAY ENCOUNTER SOUTHWESTERLY VERTICAL WIND SHEAR AND DRIER AIR AT THE MID-LEVELS. IN ADDITION...THE UPPER-LEVEL WIND FORECASTS FROM THE DYNAMICAL MODELS BECOME QUITE DIVERGENT BETWEEN 72-120 HOURS...WITH THE POSSIBILITIES RANGING FROM CONDITIONS FAVORABLE FOR INTENSIFICATION TO SHEAR STRONG ENOUGH TO CAUSE DORIAN TO WEAKEN. OVERALL...THE INTENSITY GUIDANCE FORECASTS LITTLE CHANGE IN STRENGTH DURING THE NEXT FIVE DAYS...AND THUS THE NEW FORECAST IS THE SAME AS THE PREVIOUS FORECAST. THE NEW FORECAST IS IN BEST AGREEMENT WITH THE SHIPS MODEL AND IS STRONGER THAN THE INTENSITY CONSENSUS. FORECAST POSITIONS AND MAX WINDS INIT 25/0900Z 15.6N 34.5W 50 KT 60 MPH 12H 25/1800Z 16.3N 37.0W 50 KT 60 MPH 24H 26/0600Z 17.0N 40.5W 50 KT 60 MPH 36H 26/1800Z 17.8N 44.4W 50 KT 60 MPH 48H 27/0600Z 18.3N 48.3W 50 KT 60 MPH 72H 28/0600Z 19.5N 55.5W 55 KT 65 MPH 96H 29/0600Z 20.5N 62.0W 55 KT 65 MPH 120H 30/0600Z 21.5N 67.0W 55 KT 65 MPH $$ FORECASTER BEVEN

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Tropical Storm DORIAN Forecast Discussion Number 4

2013-07-25 04:47:27| National Hurricane Center (Atlantic)

Issued at 1100 PM AST WED JUL 24 2013 000 WTNT44 KNHC 250247 TCDAT4 TROPICAL STORM DORIAN DISCUSSION NUMBER 4 NWS NATIONAL HURRICANE CENTER MIAMI FL AL042013 1100 PM AST WED JUL 24 2013 INFRARED SATELLITE IMAGERY INDICATES THAT THE LOW-LEVEL CENTER OF DORIAN HAS BECOME MORE EMBEDDED BENEATH THE COLD CONVECTIVE TOPS. DVORAK ESTIMATES FROM TAFB AND SAB ARE NOW A CONSENSUS T3.0/45 KT WHILE UW-CIMSS OBJECTIVE ESTIMATES HAVE INCREASED TO 50-55 KT. BASED ON RECENT ASCAT DATA...HOWEVER...DORIAN MAY NOT BE PRODUCING SURFACE WINDS ANY HIGHER THAN ABOUT 40 KT. THIS COULD BE DUE TO THE RESOLUTION OF ASCAT SINCE DORIAN IS A SMALL CYCLONE...SO THE INTENSITY IS BEING HELD AT 45 KT ON THIS ADVISORY. THE MOTION REMAINS 285/17 KT WITH DORIAN LYING ON THE WESTERN PERIPHERY OF A NORTHWEST-TO-SOUTHEAST ORIENTED MID-LEVEL RIDGE. A MID-LEVEL ANTICYCLONE IS EXPECTED TO DETACH FROM THE RIDGE AND MOVE WESTWARD TO THE NORTH OF DORIAN FOR THE ENTIRE FORECAST PERIOD... KEEPING THE TROPICAL CYCLONE ON A QUICK WEST-NORTHWESTWARD TO WESTWARD TRAJECTORY. THERE IS VERY LITTLE SPREAD AMONG THE TRACK MODELS ON THIS CYCLE...AND THE NEW NHC TRACK FORECAST IS VERY SIMILAR TO THE PREVIOUS TRACK. AN ANIMATION OF SEA SURFACE TEMPERATURE FIELDS INDICATES THAT THE WATERS AHEAD OF DORIAN HAVE BEEN WARMING OVER THE PAST FEW DAYS...AND IT APPEARS THAT THE CYCLONE WILL LIKELY REMAIN OVER WATERS A LITTLE WARMER THAN PREVIOUSLY ANTICIPATED. IN ADDITION...DORIAN SHOULD BE MOVING FAST ENOUGH THAT UPWELLING OF COOLER WATER SHOULD NOT BE MUCH OF A FACTOR. THEREFORE...THE NEW NHC INTENSITY FORECAST NO LONGER SHOWS SHORT-TERM WEAKENING AND INSTEAD INDICATES SLIGHT STRENGTHENING THROUGH DAY 5. THIS FORECAST IS JUST A LITTLE HIGHER THAN THE FLORIDA STATE SUPERENSEMBLE AND THE INTENSITY CONSENSUS...BUT NOT NEARLY AS HIGH AS THE STATISTICAL-DYNAMICAL SHIPS AND LGEM MODELS. CONFIDENCE IN THE INTENSITY FORECAST IS RATHER LOW AT THIS POINT UNTIL WE KNOW HOW DORIAN FARES OVER THE NEXT DAY OR TWO. FORECAST POSITIONS AND MAX WINDS INIT 25/0300Z 15.1N 33.2W 45 KT 50 MPH 12H 25/1200Z 15.7N 35.7W 50 KT 60 MPH 24H 26/0000Z 16.5N 39.0W 50 KT 60 MPH 36H 26/1200Z 17.2N 42.5W 50 KT 60 MPH 48H 27/0000Z 17.9N 46.3W 50 KT 60 MPH 72H 28/0000Z 19.0N 54.0W 55 KT 65 MPH 96H 29/0000Z 20.0N 60.5W 55 KT 65 MPH 120H 30/0000Z 20.5N 65.5W 55 KT 65 MPH $$ FORECASTER BERG

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