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Tropical Storm Roslyn Discussion Number 5
NWS National Hurricane Center Miami FL EP192022
1000 PM CDT Thu Oct 20 2022
Roslyn looks better organized on satellite imagery this evening.
Deep convection has increased near and over the estimated center
position, and the expanding dense convective overcast has cloud tops
colder than -75 to -80 deg C. The objective UW-CIMSS ADT and SATCON
estimates have increased to 40-45 kt, and SAB and TAFB provided
consensus T3.0/45 kt Dvorak estimates at 00 UTC. Based on these
data, the initial intensity is raised to 45 kt for this advisory.
Roslyn is moving west-northwestward at 285/7 kt, steered by a
mid-level ridge to the north and northwest of the cyclone. As this
ridge shifts eastward during the next couple of days, the cyclone
will become steered by the flow between the ridge and a deep-layer
trough to the northwest, well offshore of southern California. This
should induce a turn toward the north and north-northeast this
weekend, eventually bringing the center of Roslyn inland along the
coast of west-central Mexico. There is still a large spread in the
track guidance beyond 48 h regarding how sharply the cyclone
recurves and how fast it moves inland. The GFS remains on the right
side of the guidance envelope and brings Roslyn inland early Sunday,
while several other models show a slower and more gradual
recurvature with landfall later in the day. Overall, little change
was made to the NHC track forecast, which still lies slightly east
of the TVCE and HCCA aids.
The cyclone will move over warm sea surface temperatures within a
weak deep-layer shear environment during the next couple of days or
so. This is expected to support strengthening, and Roslyn is
forecast to become a hurricane by late Friday with continued
intensification over the weekend. Given the favorable environmental
conditions, the NHC intensity forecast lies on the high end of the
guidance, generally between the IVCN and HCCA aids. While rapid
intensification is not explicitly forecast, the GFS-based DTOPS
guidance shows a 44 percent chance of a 25-kt increase in intensity
during the next 24 h. Beyond 48 h, the intensity will be dependent
on the cyclone's track and whether it remains far enough offshore to
avoid the negative influences of land. The official forecast shows
Roslyn inland and rapidly weakening by 72 h, with dissipation soon
thereafter over the mountains of western Mexico.
Key Messages:
1. Roslyn is forecast to become a hurricane before it passes near or
over the west-central coast of Mexico late Saturday and Sunday,
accompanied by strong winds and a potentially dangerous storm surge.
A Hurricane Watch has been issued for the coast of mainland Mexico
from Playa Perula northward to San Blas, and additional watches or
warnings will likely be required on Friday.
2. Heavy rainfall could lead to flash flooding and possible
landslides in areas of rugged terrain over coastal southwestern and
west-central Mexico.
FORECAST POSITIONS AND MAX WINDS
INIT 21/0300Z 15.7N 103.6W 45 KT 50 MPH
12H 21/1200Z 16.0N 104.4W 55 KT 65 MPH
24H 22/0000Z 16.7N 105.3W 65 KT 75 MPH
36H 22/1200Z 17.9N 106.2W 75 KT 85 MPH
48H 23/0000Z 19.5N 106.6W 85 KT 100 MPH
60H 23/1200Z 21.3N 106.5W 85 KT 100 MPH
72H 24/0000Z 23.4N 105.6W 45 KT 50 MPH...INLAND
96H 25/0000Z...DISSIPATED
$$
Forecaster Reinhart
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