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Tropical Storm Arlene Discussion Number   8
NWS National Hurricane Center Miami FL       AL012017
500 AM AST Fri Apr 21 2017

Arlene has maintained a small area of deep convection surrounding
the center of the cyclone, with some of the cloud tops as cold as
-50 deg C. However, satellite trends over the past couple of hours
indicate that the areal coverage of the convection has decreased
significantly since the 0600 UTC satellite intensity estimates, an
indication that Arlene is beginning to lose its tropical
characteristics as the cyclone interacts with a frontal zone and
also moves over cooler water. Dvorak current intensity estimates
remain at 45 kt, and that is the intensity used for this advisory.

The initial motion estimate is now 270/27 kt.  Arlene has
accelerated westward during the past 6 hours as the cyclone moves
around the northern periphery of a larger deep-layer extratropical
low that has remained nearly stationary near 36N 48W. The small
cyclone or its remnants are expected to move in a cyclonic loop
around this low for the next couple of days.

Arlene is gradually running out of space within the narrow warm
sector of the aforementioned occluded low pressure system, and
merger with one or more frontal zones is likely during the next 12
hours. The new official intensity forecast continues the trend of
the previous advisory, which shows Arlene degenerating to a
post-tropical cyclone by 12 hours, and dissipating by 24 hours when
the system is expected to be absorbed into the larger baroclinic
low.

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  21/0900Z 40.0N  48.0W   45 KT  50 MPH
 12H  21/1800Z 39.5N  50.4W   40 KT  45 MPH...POST-TROPICAL
 24H  22/0600Z...DISSIPATED

$$
Forecaster Stewart

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