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TROPICAL STORM ERIKA DISCUSSION NUMBER   5
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL052015
1100 PM AST TUE AUG 25 2015

Both NOAA and Air Force hurricane hunter planes investigated Erika
and found a disorganized storm. The central pressure rose to 1006
mb, and the strongest winds were confined to the eastern semicircle.
The low-level center remains exposed to the north of the limited
thunderstorm activity. Based on the current appearance on satellite
imagery, and data from the plane, the initial intensity is
generously kept at 35 kt.

The intensity forecast continues to be highly uncertain. Erika
has a large cyclonic envelope, and this is a favorable factor
for the cyclone to strengthen. However, SHIPS model forecasts
a hostile west-northwesterly shear over the cyclone and, in fact, it
only strengthens Erika a little bit at the end of the forecast
period. This coincides with the solution of the GFS and the ECMWF
global models which either weaken the cyclone or show little
change in strength. The NHC forecast follows the intensity
consensus, and shows a modest strengthening beyond 3 days. By then,
the cyclone is expected to be near the Bahamas where the environment
could be a little more favorable for intensification. However, I
will not be a surprised if Erika dissipates like Danny in the
the northeastern Caribbean Sea where the environment is hostile.

Erika is embedded within the easterly flow south of a moderate
subtropical ridge which is covering the western Atlantic. This
pattern will likely continue to steer Erika between the west and
west-northwest at about 15 kt for the next 2 to 3 days. As the
cyclone reaches the western edge of the ridge in the area of the
Bahamas, the cyclone is then expected to decrease in forward speed.
The NHC forecast is very similar to the previous one and follows
very closely the multi-model consensus.

Tropical storm watches and warnings have been adjusted and added for
some of the islands of the northeastern Caribbean by the respective
Meteorological Services.


FORECAST POSITIONS AND MAX WINDS

INIT  26/0300Z 16.0N  54.4W   35 KT  40 MPH
 12H  26/1200Z 16.4N  56.9W   35 KT  40 MPH
 24H  27/0000Z 17.0N  60.1W   35 KT  40 MPH
 36H  27/1200Z 17.8N  63.2W   40 KT  45 MPH
 48H  28/0000Z 18.8N  66.0W   40 KT  45 MPH
 72H  29/0000Z 21.0N  70.9W   45 KT  50 MPH
 96H  30/0000Z 23.0N  75.0W   55 KT  65 MPH
120H  31/0000Z 26.0N  78.5W   65 KT  75 MPH

$$
Forecaster Avila

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