ZCZC MIATCDAT5 ALL
TTAA00 KNHC DDHHMM

TROPICAL STORM ERIKA DISCUSSION NUMBER   8
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL052015
500 PM AST WED AUG 26 2015

The satellite presentation of the tropical storm has become less
organized since the previous advisory, with the low-level center
becoming exposed to the northwest of the thunderstorm activity.
A NOAA Hurricane Hunter aircraft investigating Erika this afternoon
has not found flight-level or SFMR winds as strong as reported this
morning, but the aircraft did not sample much of the eastern portion
of the circulation.  The initial intensity is held at 40 kt, but
this could be generous.

The intensity forecast philosophy has not changed since this
morning.  Erika is forecast to move through an area of moderate to
strong westerly shear during the next two to three days. Although
the NHC intensity forecast during that time shows no change in
intensity, weakening is possible during the next couple of days.  In
fact, Erika could degenerate into a trough of low pressure due to
the shear and interaction with the Greater Antilles.  After 72
hours, the upper-level environment is forecast to become more
conducive for development and all of the guidance, including the
global models, shows intensification. Therefore, the days 4 and 5
intensity forecast again calls for strengthening, but is below the
intensity consensus and near the SHIPS model.  The official forecast
leans toward the lower side of the guidance to reflect the
possibility that the cyclone's structure would be too disrupted to
fully take advantage of the more conducive environment late in the
period.

The initial motion remains 280/15 kt.  Erika is forecast to move
west-northwestward during the next three to four days to the south
of a subtropical ridge over the western Atlantic.  After that time,
the global models show a weakness in the ridge developing over the
far western Atlantic, which should cause Erika to turn
northwestward.  All of the models have shifted eastward at days
four and five, but the normally reliable GFS and ECMWF define
the western edge of the guidance.  Out of respect of
these models and the previous NHC forecast, the updated track
has only been moved slightly eastward late in the period.  As a
result, the new forecast lies west of the multi-model consensus at
96 and 120 h. One should remember to not focus on the exact forecast
track, especially at the long range where the average NHC track
errors during the past 5 years are about 180 miles at day 4 and 240
miles at day 5.


FORECAST POSITIONS AND MAX WINDS

INIT  26/2100Z 16.6N  58.9W   40 KT  45 MPH
 12H  27/0600Z 17.1N  61.2W   40 KT  45 MPH
 24H  27/1800Z 18.1N  64.0W   40 KT  45 MPH
 36H  28/0600Z 19.2N  66.8W   40 KT  45 MPH
 48H  28/1800Z 20.5N  69.6W   40 KT  45 MPH
 72H  29/1800Z 22.7N  74.3W   40 KT  45 MPH
 96H  30/1800Z 25.0N  77.7W   55 KT  65 MPH
120H  31/1800Z 27.5N  80.0W   65 KT  75 MPH

$$
Forecaster Brown

NNNN