Eastern Pacific Basin Tropical Cyclones

Tropical Storm Roslyn Forecast Discussion


000
WTPZ44 KNHC 210243
TCDEP4

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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