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TROPICAL STORM DORA DISCUSSION NUMBER   6
NATIONAL WEATHER SERVICE MIAMI FL
2 AM PDT SAT AUG 07 1999
 
THE INITIAL MOTION ESTIMATE IS 285/13.  THIS IS TWO KNOTS SLOWER
THAN THE PREVIOUS ADVISORY AND THE MOTION COULD BE EVEN SLOWER IF
THE SURFACE CENTER IS DIRECTLY UNDER THE SMALL PERSISTENT CDO. 
HOWEVER I AM RELUCTANT TO CHANGE THE MOTION VERY MUCH ON THE BASIS
OF INFRARED TRACKING.  THE GFDL AND NOGAPS MODELS SHOW THE STORM
SLOWING TO UNDER 8 KNOTS DURING THE NEXT 72 HOURS.  THE UKMET MODEL
IS ALSO SLOW BUT NOT AS SLOW AS THE TWO MENTIONED ABOVE.  THIS
DECELERATION IS PROBABLY ASSOCIATED WITH THE PRESENCE OF A UPPER LOW
NEAR CALIFORNIA WHICH IS CAUSING A WEAKNESS IN THE SUBTROPICAL RIDGE
TO ITS SOUTH WHICH SHOULD SLOW DOWN THE STORM.  THE 00Z AVIATION
MODEL SUGGESTS THE RIDGE WILL NOT TOTALLY ERODE AND DORA IS
THEREFORE EXPECTED TO CONTINUE MOSTLY WESTWARD.  THE LBAR...BAM
MODELS...AND STATISTICAL DYNAMICAL MODELS ARE ALL FASTER.  THE
OFFICIAL TRACK FORECAST IS SLOWED DOWN JUST A LITTLE FROM THE
PREVIOUS ADVISORY.

DVORAK ESTIMATES REMAIN THE SAME AS SIX HOURS AGO AND THE INITIAL
WIND SPEED IS KEPT AT 45 KNOTS.  IF THE CENTER IS RIGHT UNDER THE
CDO...THE INTENSITY COULD BE HIGHER.  THE SHIPS MODEL CALLS FOR 82
KNOTS IN 60 HOURS COMPARED TO 85 KNOTS IN 60 HOURS SIX HOURS AGO. 
THIS IS BECAUSE THE PAST SIX HOUR TREND WENT FROM PLUS 10 KNOTS AT
00Z TO PLUS ZERO KNOTS AT 06Z.  THE OFFICIAL INTENSITY FORECAST IS
CHANGED LITTLE FROM THE PREVIOUS ADVISORY AND REACHES 85 KNOTS IN 72
HOURS.

LAWRENCE
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL     07/0900Z 14.1N 108.5W    45 KTS
12HR VT     07/1800Z 14.5N 110.3W    55 KTS
24HR VT     08/0600Z 14.9N 112.3W    65 KTS
36HR VT     08/1800Z 15.2N 114.0W    75 KTS
48HR VT     09/0600Z 15.4N 115.8W    80 KTS
72HR VT     10/0600Z 15.5N 119.5W    85 KTS
 
 
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