BWS - Bermuda Weather Service

Tropical Storm Fred, once a Hurricane that made a rare impact on the Cape Verde Islands, is now facing an increasingly hostile environment as it continues to move west, then northwestward across the eastern tropical Atlantic. TS Fred is expected to weaken to a tropical depression in the next day or so, and then become post-tropical/remnant low not long after. This is because it is encountering increasingly strong westerly wind shear (20-30 knots), large areas or dry air associated with Saharan dust (aka SAL or the Saharan Air Layer), and decreasing sea surface temperatures. The image from CIMSS (Cooperative Institute for Meteorological Satellite Studies) below shows an infra-red satellite image with additional layers of Saharan dust in yellow/orange and wind shear speed contours in yellow with associated directional contours in white.

000
WTNT41 KNHC 041446
TCDAT1

TROPICAL DEPRESSION FRED DISCUSSION NUMBER  23
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL062015
1100 AM AST FRI SEP 04 2015

Fred consists of a tight swirl of low clouds with intermittent
bursts of deep convection. There has been no scatterometer data over
the cyclone for several hours, but it appears that the circulation
is not as vigorous as it was yesterday. Dvorak T-numbers are
gradually decreasing, and on this basis, the initial intensity has
been lowered to 30 kt.

The shear is forecast to remain high during the next 48 hours or so,
resulting in additional weakening. Fred is expected to become a
remnant low tonight or Saturday, however, most of the global
models suggest that the shear near the system could relax in 3
days. If Fred still exists by then, and given that the ocean is
anomalously warm in the North Atlantic, there is a chance of
regeneration. This would likely occur after Fred or its remnants
recurve into the mid-latitude westerlies.

The depression is moving toward the west or 280 degrees at 9 kt,
steered by a subtropical high to its north. A strong mid-latitude
trough is forecast by the global models to deepen in the central
Atlantic during the next 2 days, and this pattern will force Fred to
recurve northeastward. This is indicated in the NHC forecast, which
follows the reliable dynamical guidance very closely. It is
interesting to note that the GFS global model in the past couple of
runs keeps Fred lingering across the North Atlantic for more than a
week.


FORECAST POSITIONS AND MAX WINDS

INIT  04/1500Z 22.3N  38.3W   30 KT  35 MPH
 12H  05/0000Z 22.6N  39.6W   30 KT  35 MPH
 24H  05/1200Z 23.0N  41.0W   25 KT  30 MPH...POST-TROP/REMNT LOW
 36H  06/0000Z 24.0N  42.2W   25 KT  30 MPH...POST-TROP/REMNT LOW
 48H  06/1200Z 25.0N  42.5W   25 KT  30 MPH...POST-TROP/REMNT LOW
 72H  07/1200Z 28.0N  40.0W   30 KT  35 MPH...TROPICAL DEPRESSION
 96H  08/1200Z 30.5N  36.0W   30 KT  35 MPH...TROPICAL DEPRESSION
120H  09/1200Z 34.0N  31.0W   30 KT  35 MPH...TROPICAL DEPRESSION

$$
Forecaster Avila