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TROPICAL DEPRESSION ERIN DISCUSSION NUMBER  20
NATIONAL WEATHER SERVICE MIAMI FL
5 AM EDT FRI SEP 07 2001
 
THE MOTION OVER THE PAST 9 HOURS HAS BEEN 030/06 BASED ON AIR FORCE 
RECON FIXES.  ALTHOUGH THIS MOTION DIFFERS FROM THE PREVIOUS 
FORECAST TRACK OF A 330 DEGREE HEADING...THE 00Z AVIATION MODEL 
SHOWS A MOSTLY NORTHWARD TRACK FOR 24 HOURS FOLLOWED BY A TURN 
TOWARD THE NORTH-NORTHEAST.  IT IS POSSIBLE THAT THE EASTWARD 
COMPONENT OF THE PAST 9 HOUR MOTION IS DUE TO A REFORMATION OF
THE CENTER...WHICH HAS NOT BEEN ALL THAT WELL DEFINED.
 
THE 00Z AVIATION MODEL SHOWS THE STRONG TROUGH IN THE WESTERLIES
BYPASSING ERIN AND THE NEXT MAJOR TROUGH IS ABOUT 5 DAYS AWAY FROM
THE U.S. EAST COAST.  A MID-LEVEL RIDGE IS FORECAST TO BUILD OVER
THE WESTERN NORTH ATLANTIC AND THERE IS A WEAK MID-LEVEL TROUGH TO
THE WEST OF ERIN.  THESE COMBINE TO PRODUCE A MOTION TOWARD THE
NORTH-NORTHWEST AT 5 TO 10 KNOTS FOR THE NEXT 72 HOURS.  THE
GFDL...AVN...AND UKMET AGREE ON THIS.
 
THE AIRCRAFT REPORTED 1008 MB SURFACE PRESSURE...DOWN 5 MB FROM 9
HOURS AGO.  THE HIGHEST WINDS MEASURED AT 1500 FT ALTITUDE WERE 35
KNOTS ABOUT 25 N MI NORTHEAST OF THE CENTER.  THE INITIAL WIND SPEED
IS INCREASED TO 30 KNOTS.  OTHERWISE THE INTENSITY FORECAST IS THE
SAME AS THE PREVIOUS ADVISORY...BRINGING THE DEPRESSION TO 65 KNOTS
IN 72 HOURS.  THE SHIPS MODEL DOES THE SAME AND THE GFDL IS MORE 
AGGRESSIVE.  IF THE AIRCRAFT HAD NOT FOUND A 5 MB PRESSURE DROP...I
WOULD HAVE BACKED OFF ON BRINGING ERIN TO A HURRICANE IN 72 HOURS.
 
FORECASTER LAWRENCE
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL     07/0900Z 24.7N  57.6W    30 KTS
12HR VT     07/1800Z 25.4N  57.6W    30 KTS
24HR VT     08/0600Z 26.3N  58.4W    40 KTS
36HR VT     08/1800Z 27.4N  59.4W    50 KTS
48HR VT     09/0600Z 28.6N  60.6W    60 KTS
72HR VT     10/0600Z 31.0N  63.0W    65 KTS
  
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