Subtropical Storm Rebekah Forecast Discussion

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WTNT44 KNHC 302039

Subtropical Storm Rebekah Discussion Number   1
NWS National Hurricane Center Miami FL       AL192019
500 PM AST Wed Oct 30 2019

Cloudiness and showers associated with a small low pressure system
embedded within a larger non-tropical low over the north-central
Atlantic have become better organized during the day. The cyclone
has a broken convective band that wraps about halfway around its
eastern semicircle, with a small area of central convection near its
center. The cloud tops within the convection are not particularly
cold and the system is co-located with a large upper-level low, so
it is initially designated as a subtropical cyclone. The intensity
is assessed as 40 kt based primarily on earlier ASCAT data. It is
worth mentioning that the system also has some characteristics of a
tropical cyclone, since the radius of maximum winds is not very
large and the system has some moderate central convection.

Much like Pablo just a few days ago, Rebekah is currently rotating
around a larger non-tropical low pressure system. The initial motion
estimate is 080/11 kt, but an east-northeastward motion is expected
later tonight. The track model spread is larger than normal and
confidence in the track forecast is low, though most of the models
generally show Rebekah turning back toward the east by early Friday,
followed by a turn toward the east-southeast until it dissipates
later this week. On the forecast track, the center of Rebekah is
forecast to approach the western-most Azores early Friday as a
post-tropical/extratropical cyclone.

The intensity guidance unanimously forecasts that Rebekah will
change little in strength during the next 24 h, though given the
small size of the cyclone, some short-term fluctuations are possible
tonight. Most of the dynamical models then forecast that Rebekah's
convection will decrease substantially by early Friday, likely due
to a combination of colder SSTs and unfavorable upper-level winds.
The cyclone is therefore forecast to become post-tropical around
that time, and gradual weakening is expected. Rebekah will likely
dissipate by the weekend, if not sooner.

Since Rebekah is not currently forecast to be a tropical or
subtropical cyclone when it nears the Azores, hazard information
can be found in regular products issued by the Portuguese Institute
for the Sea and Atmosphere (IPMA) for those islands.


INIT  30/2100Z 38.3N  40.7W   40 KT  45 MPH
 12H  31/0600Z 39.0N  38.4W   40 KT  45 MPH
 24H  31/1800Z 39.9N  35.0W   40 KT  45 MPH
 36H  01/0600Z 39.8N  31.3W   35 KT  40 MPH...POST-TROP/EXTRATROP
 48H  01/1800Z 38.9N  26.3W   30 KT  35 MPH...POST-TROP/EXTRATROP
 72H  02/1800Z...DISSIPATED

Forecaster Zelinsky

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