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Tropical Storm Roslyn Discussion Number 3
NWS National Hurricane Center Miami FL EP192022
1000 AM CDT Thu Oct 20 2022
Convection associated with the cyclone has become a bit better
organized since the last advisory, with a strong cluster having
developed near the center. Various subjective and objective
satellite intensity estimates are now near 35 kt, and based on this
the depression is upgraded to Tropical Storm Roslyn with an initial
intensity of 35 kt. Although the system has strengthened, recent
microwave and conventional satellite imagery suggests that multiple
low-level swirls are present near the center, indicating that the
inner core has not yet tightened up.
The initial motion is now 275/5 kt along the southern edge of a
mid-level ridge to the north and northwest of the storm. In
addition, a deep-layer low pressure area is currently located
southwest of California, and west of the ridge. These features are
forecast to move slowly eastward during the next few days, with the
deep-layer steering flow near Roslyn changing from easterly to
southeasterly to southerly and eventually to southwesterly. This
evolution should cause the storm to recurve between the ridge and
the low and make landfall in western Mexico. The track guidance is
generally in good agreement with this scenario. However, there is
some spread regarding how quickly Roslyn will recurve. The GFS is
on the right side of the guidance envelope with the center passing
near Cabo Corrientes, while the UKMET and ECMWF are farther west.
The new forecast track is similar to the previous forecast and
calls for the center to pass just west of Cabo Corrientes in about
72 h, followed by landfall in mainland Mexico before 96 h. The new
forecast track is near or a little to the east of the consensus
models.
Roslyn is currently over warm sea surface temperatures in a moist
environment with light vertical wind shear. These conditions are
likely to persist for the next 72 h or so, and they should allow
Roslyn to steadily intensify. After 72 h, the intensity forecast
becomes more uncertain due to a forecast increase in shear, the
possibility of dry air entrainment, and the possibility of land
interaction. The new NHC forecast is generally similar to the
previous forecast, although it has a slightly lower peak intensity
before landfall in mainland Mexico due to a downward trend in the
guidance. After landfall, rapid weakening is expected, with the
cyclone dissipating over the mountains of Mexico between 96-120 h.
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.
Interests along the coast of southwestern and west-central Mexico
should closely monitor the progress of this system, and hurricane
or tropical storm watches could be required for portions of this
coastline later today.
2. Heavy rainfall from Roslyn could lead to flash flooding and
possible landslides in areas of rugged terrain over coastal
southwestern Mexico.
FORECAST POSITIONS AND MAX WINDS
INIT 20/1500Z 15.2N 102.0W 35 KT 40 MPH
12H 21/0000Z 15.4N 102.8W 45 KT 50 MPH
24H 21/1200Z 15.7N 103.7W 55 KT 65 MPH
36H 22/0000Z 16.3N 104.6W 65 KT 75 MPH
48H 22/1200Z 17.2N 105.5W 75 KT 85 MPH
60H 23/0000Z 18.6N 106.0W 80 KT 90 MPH
72H 23/1200Z 20.3N 105.9W 85 KT 100 MPH
96H 24/1200Z 24.0N 104.0W 35 KT 40 MPH...INLAND
120H 25/1200Z...DISSIPATED
$$
Forecaster Beven
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