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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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