Eastern Pacific Basin Tropical Cyclones

Tropical Storm Roslyn Forecast Discussion


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WTPZ44 KNHC 201449
TCDEP4

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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