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Tropical Storm Isaac Discussion Number 6
NWS National Hurricane Center Miami FL AL092018
1100 PM AST Sat Sep 08 2018
Isaac is strengthening this evening. Satellite images indicate that
the deep convection has been increasing in intensity and coverage
with better defined banding features. The center is not located in
the center of the convection, however, due to some easterly shear.
An ASCAT pass around 00Z showed maximum winds in the 40-45 kt
range. These data are also in line with the latest Dvorak
classifications of 3.0/45 kt from TAFB and SAB. Based on these
estimates, the initial intensity is raised to 45 kt.
Isaac will likely continue to strengthen during the next few days as
the storm remains over warm waters and moves into an environment of
decreasing wind shear. Beyond a few days, the SHIPS model shows a
notable increase in shear, in part due to the outflow from Florence,
which should end the strengthening trend and cause some weakening.
With the exception of the HMON and COAMPS-TC models, the remainder
of the intensity guidance is higher this cycle. The NHC intensity
forecast is raised from the previous one, but it is a little lower
than the HCCA and IVCN guidance.
The storm is moving due westward at 7 kt. The track forecast seems
fairly straightforward. 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. This
scenario is supported by the usually more reliable GFS and ECMWF
models, and the NHC track forecast is near a blend of those aids.
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.
FORECAST POSITIONS AND MAX WINDS
INIT 09/0300Z 14.4N 37.5W 45 KT 50 MPH
12H 09/1200Z 14.4N 38.7W 50 KT 60 MPH
24H 10/0000Z 14.5N 40.9W 60 KT 70 MPH
36H 10/1200Z 14.5N 43.5W 70 KT 80 MPH
48H 11/0000Z 14.5N 46.1W 75 KT 85 MPH
72H 12/0000Z 14.5N 51.5W 85 KT 100 MPH
96H 13/0000Z 14.6N 57.0W 80 KT 90 MPH
120H 14/0000Z 15.0N 62.9W 75 KT 85 MPH