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