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Tropical Storm Rina Discussion Number   9
NWS National Hurricane Center Miami FL       AL192017
500 AM AST Wed Nov 08 2017

Satellite imagery over the past 6 hours indicates that Rina has
taken on a tight comma-cloud appearance, more indicative of a
sub-tropical cyclone than a tropical system. Although an eye-like
feature has recently developed, it appears to be tilted about 20-30
nmi to the north of the low-level center. Dvorak satellite intensity
estimates were ST3.0/45-50 kt from TAFB and T3.5 from SAB. Data
from a late-arriving, partial ASCAT-B scatterometer pass at 0029Z
indicated 46-kt surface winds well east of the center, and the cloud
pattern has improved since that time. Based these data, the
intensity of Rina has been increased to 50 kt.

Rina is moving northward or 010/17 kt. Rina is located just north
of the axis of a deep-layer ridge, which is located to the east of
the cyclone. As a result, a northward to north-northeastward motion
is expected for the next 12-24 h. Thereafter, a shortwave trough
situated to the southwest of Rina should induce acceleration toward
the northeast on Thursday, followed by a more rapid motion of 30-35
kt by Thursday night and Friday as westerly flow on the east side of
a deep-layer trough captures the system. The latest NHC model
guidance has shifted to the west some, but the official forecast
track has only been nudged slightly in that direction due to a
distinct westward bias noted in the model guidance during the past
48 hours.

Although some sight strengthening could occur during the next 6-12
hours, the overall intensity trend is forecast to change little
during the period due to the combination of cold SSTs of less than
20 deg C by 18 h and increasing vertical wind shear of more than 35
kt by 36 hours. By 24 h, Rina should become a post-tropical cyclone
over the cold waters of the far north Atlantic and become
extratropical and merge with a front by 48-72 h.

FORECAST POSITIONS AND MAX WINDS

INIT  08/0900Z 37.1N  48.4W   50 KT  60 MPH
 12H  08/1800Z 39.7N  47.7W   50 KT  60 MPH
 24H  09/0600Z 43.6N  45.7W   50 KT  60 MPH...POST-TROPICAL
 36H  09/1800Z 48.7N  40.6W   50 KT  60 MPH...POST-TROP/EXTRATROP
 48H  10/0600Z 53.3N  32.0W   45 KT  50 MPH...POST-TROP/EXTRATROP
 72H  11/0600Z...DISSIPATED

$$
Forecaster Stewart

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