Tropical Storm DORIAN

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TROPICAL STORM DORIAN DISCUSSION NUMBER   6
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL042013
1100 AM AST THU JUL 25 2013
 
CONVENTIONAL AND MICROWAVE SATELLITE IMAGERY INDICATE THAT THERE HAS
BEEN NO SIGNIFICANT CHANGE IN THE OVERALL CONVECTIVE PATTERN OR
STRUCTURE OF DORIAN SINCE THE PREVIOUS ADVISORY. THE COMPACT
TROPICAL CYCLONE HAS MAINTAINED A SMALL BUT SYMMETRIC OUTFLOW
PATTERN...ALONG WITH GOOD LOW-LEVEL EQUATORIAL INFLOW.  SATELLITE
INTENSITY ESTIMATES ARE 55 KT FROM TAFB AND AND 45 KT FROM TAFB...
SO THE INITIAL INTENSITY IS BEING MAINTAINED AT 50 KT. THE INITIAL
POSITION IS A LITTLE SOUTH OF THE CONVENTIONAL SATELLITE FIX
POSITIONS BASED ON MICROWAVE IMAGERY OVER THE PAST 6 HOURS.
 
THE INITIAL MOTION ESTIMATE IS 285/15. THERE IS ESSENTIALLY NO
CHANGE TO PREVIOUS FORECAST TRACK OR REASONING. THE NHC MODEL
GUIDANCE CONTINUES TO BE IN EXCELLENT AGREEMENT ON DORIAN MOVING IN
A GENERAL WEST-NORTHWESTWARD DIRECTION THROUGHOUT THE FORECAST
PERIOD. THE MAIN DIFFERENCE BETWEEN THE MODELS CONTINUES TO BE THE
FORWARD SPEED OF DORIAN...WITH THE ECMWF AND HWRF BEING THE FASTEST
MODELS WITH A WEAKER CYCLONE...WHILE THE GFS AND GFS-ENSEMBLE MEAN
MODELS ARE THE SLOWEST DUE TO THEIR FORECASTING A STRONGER VORTEX.
BASED ON THE BETTER PERFORMANCE OF THE GFS MODEL INTENSITY
FORECASTS OVER THE PAST FEW DAYS...THE OFFICIAL FORECAST LEANS
TOWARD THE LATTER SOLUTION AND SHOWS A GRADUAL DECREASE IN FORWARD
SPEED TO BEGIN BY 48-72 HOURS AS DORIAN APPROACHES A WEAKNESS IN
THE SUBTROPICAL RIDGE. THE NEW TRACK FORECAST IS JUST AN EXTENSION
OF THE PREVIOUS ADVISORY TRACK...AND IS VERY CLOSE TO BUT SLOWER
THAN THE CONSENSUS MODEL TVCN.
 
DORIAN APPEARS TO HAVE SURVIVED PASSAGE OVER THE REGION OF COOLEST
SSTS OVERNIGHT AND IS NOW MOVING OVER AND TOWARD WARMER WATERS.
ALTHOUGH THE AFOREMENTIONED EQUATORIAL INFLOW OF WARM UNSTABLE AIR
LIKELY HELPED OFFSET THE COOLING BENEATH DORIAN...THAT LIFELINE IS
FORECAST BY ALL OF THE MODELS TO BE CUT OFF DURING THE NEXT 24
HOURS...WHICH WILL RESULT IN THE COMPACT CYCLONE MOVING THROUGH A
REGION OF DECREASING MID-LEVEL MOISTURE AND MORE STABLE AIR...
PRODUCING SOME SLIGHT WEAKENING FOR THE NEXT 24 HOURS OR SO. AFTER
THAT...THE VERTICAL SHEAR IS EXPECTED TO REMAIN AT OR BELOW 10-15
KT...WHICH WOULD FAVOR AT LEAST SOME GRADUAL INTENSIFICATION IF THE
INNER CORE CONVECTION CAN REMAIN INTACT. THE OFFICIAL INTENSITY
FORECAST LIES BETWEEN THE SHIPS AND LGEM SOLUTIONS...AND ASSUMES
DORIAN WILL SURVIVE ITS TREK THROUGH UNFAVORABLE THERMODYNAMIC
CONDITIONS DURING THE NEXT 2 DAYS.
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  25/1500Z 16.0N  35.9W   50 KT  60 MPH
 12H  26/0000Z 16.6N  38.5W   45 KT  50 MPH
 24H  26/1200Z 17.4N  42.3W   45 KT  50 MPH
 36H  27/0000Z 18.0N  46.2W   50 KT  60 MPH
 48H  27/1200Z 18.7N  49.9W   50 KT  60 MPH
 72H  28/1200Z 19.8N  57.0W   55 KT  65 MPH
 96H  29/1200Z 20.7N  63.0W   60 KT  70 MPH
120H  30/1200Z 21.5N  67.5W   60 KT  70 MPH
 
$$
FORECASTER STEWART
 
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