[Tropical] Tropical Cyclone Discussion

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WTNT43 KNHC 292035
TCDAT3

Tropical Storm Rina Discussion Number   6
NWS National Hurricane Center Miami FL       AL182023
500 PM AST Fri Sep 29 2023

Strong northwesterly shear has caused the low-level center of Rina
to become completely exposed today. The overall convective structure
of the storm has deteriorated as well, with only small bursts of
deep convection observed in satellite images well downshear of its
center. An earlier scatterometer pass did not sample the core of the
system, but still showed 30-35 kt winds well removed from the center
in the southeast quadrant. The latest objective and subjective
satellite intensity estimates range from 30-45 kt, and the initial
intensity is conservatively held at 40 kt this afternoon. A full
scatterometer pass should be available this evening to better assess
the current intensity of Rina.

The tropical cyclone has turned northwestward and is accelerating,
with an initial motion of 320/8 kt. This general motion with a
slight increase in forward speed is expected during couple of days
while Rina moves around the northeastern periphery of the broader
circulation associated with Tropical Storm Philippe. Thereafter, the
shallow cyclone is forecast to separate from Philippe and turn
north-northwestward between a subtropical ridge to the east and an
approaching frontal system over the western Atlantic. There is still
large spread in the track guidance regarding the extent and speed of
this turn, with the GFS still on the western edge of the guidance.
With this uncertainty in mind, the updated NHC forecast remains
close to the HCCA and TVCA consensus aids and lies near the center
of the guidance envelope.

The strong wind shear currently affecting Rina is unlikely to relent
during the next couple of days. So despite warm SSTs along its path,
Rina seems unlikely to sustain a more organized convective structure
going forward, which is consistent with simulated satellite imagery
from the global models. The NHC intensity forecast shows gradual
weakening during the next several days, following the latest
multi-model intensity consensus aids. By 96 h, Rina is forecast to
open into a trough and/or merge with a frontal system. But if the
center remains decoupled from the convection, it is possible that
Rina degenerates into a remnant low even sooner than forecast.


FORECAST POSITIONS AND MAX WINDS

INIT  29/2100Z 20.0N  47.8W   40 KT  45 MPH
 12H  30/0600Z 20.5N  48.8W   40 KT  45 MPH
 24H  30/1800Z 21.4N  50.2W   40 KT  45 MPH
 36H  01/0600Z 22.8N  52.0W   35 KT  40 MPH
 48H  01/1800Z 24.4N  53.8W   35 KT  40 MPH
 60H  02/0600Z 25.9N  55.1W   30 KT  35 MPH
 72H  02/1800Z 27.8N  55.7W   25 KT  30 MPH...POST-TROP/REMNT LOW
 96H  03/1800Z...DISSIPATED

$$
Forecaster B. Reinhart/A. Reinhart
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