Tropical Storm DORIAN

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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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