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SUBTROPICAL STORM ALEX DISCUSSION NUMBER 1
NWS NATIONAL HURRICANE CENTER MIAMI FL AL012016
500 PM AST WED JAN 13 2016
Curved bands of cloudiness and showers/thunderstorms associated with
the low pressure system over the eastern subtropical Atlantic have
become better defined over the past 24 hours. Although the
convection is not very deep, it is likely of at least moderate
intensity given the relatively shallow tropospause over the area.
Given the increased organization, and the apparent dissipation of
nearby frontal features, advisories are being initiated at this
time. The cyclone is co-located with an upper-level low, and
appears to have only a weak warm core, so it is being designated
as a subtropical storm. The current intensity is set to 45 kt in
agreement with an earlier scatterometer overpass. A ship traversed
the northern portion of the circulation earlier today and did not
observe winds of tropical storm force and this is reflected in the
advisory wind radii.
The cyclone has been turning toward the left as it moves in the
flow on the east side of a shortwave trough, and the initial motion
is northeastward or 055/12 kt. The trough is expected to continue
to swing counterclockwise around a broader mid-latitude cyclonic
gyre, and this should result in Alex turning northward and
north-northwestward over the next several days. The official
forecast track follows the dynamical model consensus.
Although the shear is not forecast to become very strong over the
next several days, the cyclone will be moving over progressively
colder waters. Therefore no increase in strength is shown for the
next day or so. In the latter part of the forecast period, some
strengthening is possible due to baroclinic processes. By 96
hours, the global models show the cyclone merging or becoming
absorbed by another extratropical low at high latitudes.
Alex is expected to become an extratropical cyclone by the time it
passes near or over the Azores, so no tropical storm warnings are
being issued for those islands. However, gale force winds are
likely to affect portions of the Azores beginning late on Thursday
or early on Friday.
Alex is the first tropical or subtropical storm to form in January
since an unnamed system did so in 1978, and is only the fourth known
to form in this month in the historical record that begins in 1851.
FORECAST POSITIONS AND MAX WINDS
INIT 13/2100Z 27.1N 30.8W 45 KT 50 MPH
12H 14/0600Z 28.9N 29.7W 45 KT 50 MPH
24H 14/1800Z 32.0N 28.2W 45 KT 50 MPH
36H 15/0600Z 36.3N 27.5W 45 KT 50 MPH
48H 15/1800Z 42.3N 28.2W 50 KT 60 MPH...POST-TROP/EXTRATROP
72H 16/1800Z 56.0N 34.0W 50 KT 60 MPH...POST-TROP/EXTRATROP