Tropical Storm EARL

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TROPICAL STORM EARL DISCUSSION NUMBER   6
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   AL072010
500 PM AST THU AUG 26 2010
 
INNER-CORE CONVECTION REMAINS SHALLOW AND LOOSELY ORGANIZED...BUT
THE OVERALL CLOUD PATTERN AND STRUCTURE HAS IMPROVED AND BECOME
MORE CIRCULAR IN VISIBLE IMAGERY. AN 1150Z ASCAT PASS EARLIER THIS
MORNING INDICATED EARL POSSESSED A LARGE SWATH OF 34-KT WINDS MORE
THAN 90 NMI NORTH OF THE CENTER...WHICH WOULD SUPPORT HIGHER
NEAR-SURFACE WINDS GIVEN THE LOW BIAS OF ASCAT WINDS. THE INITIAL
INTENSITY WILL REMAIN 40 KT FOR THIS ADVISORY BASED ON A BLEND OF
SATELLITE CURRENT INTENSITY ESTIMATES OF 45 KT AND 35 KT FROM TAFB
AND SAB...RESPECTIVELY..AND THE AFOREMENTIONED ASCAT WINDS. EARL
ALSO PASSED JUST NORTH OF PIRATA BUOY 13008 AROUND 1800Z...WHICH
REPORTED A PRESSURE OF 1003 MB. THIS PRESSURE VALUE WOULD ALSO
SUPPORT AN INTENSITY OF ABOUT 40 KT.
 
EARL REMAINS ON TRACK WITH AN INITIAL MOTION ESTIMATE OF 280/16. THE
OFFICIAL FORECAST TRACK REMAINS UNCHANGED THROUGH 48 HOURS AS THE
STRONG SUBTROPICAL RIDGE TO THE NORTH REMAINS IN PLACE. BY 72
HOURS...EARL IS FORECAST TO APPROACH A WEAKNESS IN THE RIDGE AXIS
INDUCED BY DANIELLE AND A MID-LATITUDE TROUGH THAT IS FORECAST TO
HELP RECURVE THAT HURRICANE TO THE NORTHEAST. AS EARL APPROACHES
THE WEAKNESS IN THE RIDGE...IT IS EXPECTED TO GRADUALLY SLOW DOWN
AND TURN MORE TOWARD THE NORTHWEST. THE 12Z GFS AND ECMWF MODELS
ARE NOW FORECASTING DANIELLE TO RECURVE TO THE NORTHEAST FASTER
THAN PREVIOUSLY EXPECTED...WHICH ALSO ALLOWS THE SUBTROPICAL RIDGE
BETWEEN EARL AND DANIELLE TO BUILD BACK IN TO THE NORTH OF EARL.
THIS DEVELOPING FLOW PATTERN WOULD FORCE EARL MORE WESTWARD THAN
NORTHWARD AT A SLOWER FORWARD SPEED BY DAYS 4 AND 5. THE OFFICIAL
FORECAST TRACK IS JUST AN UPDATE OF THE PREVIOUS TRACK THROUGH 72
HOURS...AND THEN A LITTLE TO THE LEFT OF THE PREVIOUS ADVISORY
AFTER THAT. THE FORECAST REMAINS ON THE NORTHERN OR RIGHT EDGE OF
THE GUIDANCE ENVELOPE IN THE EVENT THE CIRCULATION CENTER
REDEVELOPS FARTHER NORTH WITHIN THE BROAD CONVECTIVE CLOUD MASS.
 
ALTHOUGH THE MODELS CONTINUE TO FORECAST LOW VERTICAL SHEAR ACROSS
EARL THROUGH THE NEXT 24-36 HOURS...THE CYCLONE STILL HAS TO
TRAVERSE THROUGH AN ENVIRONMENT OF DRY MID-LEVEL AIR. BY 48
HOURS...SOME OF THE NORTHERLY OUTFLOW ON THE EAST SIDE OF HURRICANE
DANIELLE IS EXPECTED TO CREATE SOME MODEST NORTHERLY SHEAR ACROSS
EARL...WHICH MAY INHIBIT THE DEVELOPMENT PROCESS. HOWEVER...BY DAYS
4 AND 5...THE UPPER-LEVEL FLOW PATTERN IS FORECAST TO BECOME MORE
FAVORABLE FOR DEVELOPMENT AS EARL MOVES INTO THE SOUTHWEST
PERIPHERY OF A LARGE SYNOPTIC-SCALE 200 MB ANTICYCLONE...WHICH
SHOULD ACT TO ENHANCE THE OUTFLOW TO THE NORTH AND SOUTH OF THE
CYCLONE. THE GFDL AND HWRF MODELS ARE ALSO INDICATING DEVELOPMENT
OF THIS FAVORABLE OUTFLOW PATTERN AND STRENGTHEN EARL TO CATEGORY 4
INTENSITY BY 120 HOURS. THE OFFICIAL INTENSITY FORECAST IS A LITTLE
LOWER THAN THE SHIPS AND LGEM MODELS THROUGH 72 HOURS AND THEN
HIGHER AT DAYS 4 AND 5...BUT NOT AS HIGH AS THE GFDL/HWRF MODELS.
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      26/2100Z 15.2N  38.8W    40 KT
 12HR VT     27/0600Z 15.6N  41.2W    45 KT
 24HR VT     27/1800Z 15.9N  44.4W    55 KT
 36HR VT     28/0600Z 16.3N  47.7W    60 KT
 48HR VT     28/1800Z 16.7N  50.8W    65 KT
 72HR VT     29/1800Z 18.2N  55.9W    75 KT
 96HR VT     30/1800Z 20.6N  60.0W    85 KT
120HR VT     31/1800Z 23.0N  62.5W   100 KT
 
$$
FORECASTER STEWART
 
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