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TROPICAL STORM ERIKA DISCUSSION NUMBER  18
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL052015
500 AM EDT SAT AUG 29 2015

Erika remains very disorganized with the deep convection still
displaced well east and southeast of the apparent center. The
initial intensity has been set at 35 kt based on the latest Dvorak
classification from TAFB, and these winds are likely occurring well
east and northeast of the center. Erika will have to contend with
land interaction and strong shear for the next day or so, which
should result in the cyclone weakening to a depression later today,
if not dissipating entirely. Assuming Erika survives the next 24
hours, some restrengthening is possible over the Gulf of Mexico in a
less hostile environment. The low-confidence NHC intensity forecast
is similar to the previous one and below the latest intensity
consensus.

The disorganized center of Erika has been difficult to locate, but
my best estimate of the initial motion is 290/17, with the center
moving a little to the left of the previous forecast track. Erika
should gradually turn toward the northwest and decelerate during the
next 36 to 48 hours as it moves around the edge of the subtropical
ridge. After that time a northward motion at an even slower forward
speed is expected. The new NHC track has been adjusted to the left,
especially during the first 48 hours, due to the initial position
and motion, and is largely an update of the previous forecast after
that time. The NHC forecast is close to the multi-model consensus
through 48 hours and is between the consensus and the GFS model
after that time. Given the uncertainty in the initial position and
motion, and whether Erika even has a closed center, confidence in
the details of the track forecast remains low.

The greatest short-term threat posed by Erika continues to be very
heavy rainfall over portions of Hispaniola and eastern Cuba. These
rains could produce flash floods and mudslides.

Although this would normally be an appropriate time for a tropical
storm watch for portions of southern Florida following typical
timelines, we have elected to wait until later today to see if the
circulation of Erika has survived its interaction with Hispaniola.
An Air Force Reserve Hurricane Hunter aircraft will be investigating
Erika later this morning. There is a significant chance that no
watches or warnings for Florida will be required.

FORECAST POSITIONS AND MAX WINDS

INIT  29/0900Z 19.1N  75.1W   35 KT  40 MPH
 12H  29/1800Z 20.3N  77.5W   30 KT  35 MPH
 24H  30/0600Z 22.3N  80.3W   30 KT  35 MPH...INLAND
 36H  30/1800Z 24.0N  82.1W   30 KT  35 MPH...OVER WATER
 48H  31/0600Z 25.3N  83.2W   35 KT  40 MPH
 72H  01/0600Z 27.0N  84.0W   35 KT  40 MPH
 96H  02/0600Z 29.5N  84.5W   40 KT  45 MPH
120H  03/0600Z 31.0N  84.5W   25 KT  30 MPH...INLAND

$$
Forecaster Brennan

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