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Tropical Storm Arlene Discussion Number   7
NWS National Hurricane Center Miami FL       AL012017
1100 PM AST Thu Apr 20 2017

Despite increasing involvement with a frontal zone, Arlene
continues to produce organized convection in infrared imagery and to
show good low-level organization in microwave imagery.  A partial
ASCAT overpass showed a few 40 kt vectors well to the northeast of
the center, and based on this the initial intensity is increased to
45 kt.  Unfortunately, the scatterometer data did not cover the
central core and could not answer the question of whether the storm
still has a closed circulation.  Based on the available data, Arlene
remains a tropical storm for this advisory.  However, it could
become extratropical, lose convection and become post-tropical, or
degenerate into a trough at any time during the next 12 to 24 hours.
The official forecast has the system degenerating to a post-tropical
low in 12 hours and then dissipating as it is absorbed into a
baroclinic low.

The initial motion is 305/24.  Arlene is being steered by the
aforementioned deep-layer baroclinic low centered near 36N 48W, and
the tropical cyclone,  or its remnants, is expected to move in a
cyclonic loop around this low for the next few days.

Tropical storms in April are rare and Arlene is only the second
one observed in this month during the satellite era. It should be
noted, however, that this type of storm was practically impossible
to detect prior to the weather satellite era.


FORECAST POSITIONS AND MAX WINDS

INIT  21/0300Z 39.4N  44.2W   45 KT  50 MPH
 12H  21/1200Z 40.0N  48.0W   40 KT  45 MPH...POST-TROPICAL
 24H  22/0000Z...DISSIPATED

$$
Forecaster Beven

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