Official Discussion issued by the National Hurricane Center

Isaac (AL092018) DATA RELEASED: 9/9/2018 5:00:00 AM UTC

Copy of official data

Tropical Storm Isaac Discussion Number   7
NWS National Hurricane Center Miami FL       AL092018
500 AM AST Sun Sep 09 2018

The cloud pattern of Isaac has changed significantly during the past
several hours.  The storm no longer has a sheared appearance, and
instead microwave images reveal a well-defined curved band that
wraps a little more than halfway around the center.  Despite the
change in the storm's structure, the Dvorak classifications are
unchanged at 3.0/45 kt.  Based on that data, the initial intensity
is held at 45 kt for this advisory.

Now that the shear has lessened, Isaac should steadily strengthen
during the next few days as the storm remains over warm waters and
in a low wind shear environment.  Beyond a few days, however, the
SHIPS model shows a notable increase in shear, in part due to the
outflow from Florence, which should end the strengthening trend and
induce some weakening.  There was no significant change in the
intensity guidance this cycle, so the official forecast is largely
an update of the previous one.  This prediction lies fairly
close to the IVCN and HCCA models.

Isaac remains on the forecast track and the initial motion is the
same as before, 270/7.  A strengthening subtropical ridge to the
north of the system should cause Isaac to move westward at an
increasing forward speed during the next several days.  Although
there is some spread in the models, the usually more reliable GFS
and ECMWF models have been consistent in showing a due westward
motion through the forecast period.  The NHC track forecast leans
toward those models, and it is fairly similar to the previous
prediction. Based on the current forecast, Isaac will be near the
Lesser Antilles in 4 to 5 days and interests there should monitor
the progress of this system.


INIT  09/0900Z 14.5N  38.1W   45 KT  50 MPH
12H  09/1800Z 14.6N  39.6W   55 KT  65 MPH
24H  10/0600Z 14.7N  41.9W   60 KT  70 MPH
36H  10/1800Z 14.7N  44.6W   70 KT  80 MPH
48H  11/0600Z 14.7N  47.5W   80 KT  90 MPH
72H  12/0600Z 14.7N  53.1W   85 KT 100 MPH
96H  13/0600Z 14.9N  58.9W   80 KT  90 MPH
120H  14/0600Z 15.3N  64.5W   70 KT  80 MPH

Forecaster Cangialosi