Eastern Pacific Basin Tropical Cyclones

Tropical Storm Roslyn Forecast Discussion


000
WTPZ44 KNHC 202036
TCDEP4

Tropical Storm Roslyn Discussion Number   4
NWS National Hurricane Center Miami FL       EP192022
400 PM CDT Thu Oct 20 2022

Satellite imagery shows that Roslyn has become a little more 
organized this afternoon, with the formation of a curved convective 
band near the center in the eastern semicircle.  The various 
subjective and objective satellite intensity estimates have 
increased a little since the last advisory, and the initial 
intensity is increased to 40 kt in best agreement with the CIMSS 
satellite consensus.  It should be noted that Roslyn looks a little 
sheared, with the center near the western edge of the convection 
and a lot of curved low cloud lines apparent west of the 
convection.  It is uncertain why the cyclone looks this way since 
the analyzed vertical wind shear is less than 10 kt.

The initial motion is now 280/6 kt.  A mid- to upper-level ridge is 
located over Mexico north and northwest of Roslyn, while a 
deep-layer low pressure area is located several hundred miles 
southwest of the coast of southern California.  The large-scale 
models forecast both of these features to move eastward, with Roslyn 
expected to recurve to the north and northeast between them. While 
the track guidance is in good agreement with this general scenario, 
there is a significant spread in the guidance regarding how far west 
the cyclone will move before recurvature.  The GFS is on the right 
side of the envelope, bringing the center near Cabo Corrientes in 
roughly 60 h and inland over mainland Mexico thereafter.  On the 
other hand, the ECMWF and UKMET are about 150 n mi west of the GFS 
at that time, keeping the center farther offshore and showing a 
more northerly landfall point in mainland Mexico.  Overall, the 
guidance envelope has shifted a little to the west since the last 
advisory.  The new forecast track is also shifted west of the 
previous track, but it lies to the east of the consensus models out 
of deference to the previous forecast and the GFS.

Roslyn remains over warm sea surface temperatures in a moist, 
light-shear environment.  These conditions are likely to persist 
for the next 60-72 h, and they should allow Roslyn to steadily 
intensify.  After that time, the intensity forecast becomes more 
uncertain due to a forecast increase in shear, the possibility of 
dry air entrainment, and the uncertainty of how much land 
interaction will occur.  The new intensity forecast is again 
similar to the previous forecast and calls for a peak intensity of 
85 kt before landfall in mainland Mexico.  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.  A tropical 
storm watch has been issued for part of this area, and additional 
hurricane or tropical storm watches could be required tonight or 
on Friday.

2. Heavy rainfall could lead to flash flooding and possible 
landslides in areas of rugged terrain over coastal southwestern 
Mexico.


FORECAST POSITIONS AND MAX WINDS

INIT  20/2100Z 15.5N 103.0W   40 KT  45 MPH
 12H  21/0600Z 15.8N 103.7W   45 KT  50 MPH
 24H  21/1800Z 16.3N 104.6W   55 KT  65 MPH
 36H  22/0600Z 17.2N 105.7W   65 KT  75 MPH
 48H  22/1800Z 18.5N 106.3W   75 KT  85 MPH
 60H  23/0600Z 20.0N 106.5W   85 KT 100 MPH
 72H  23/1800Z 21.8N 106.0W   85 KT 100 MPH
 96H  24/1800Z 25.0N 104.5W   25 KT  30 MPH...INLAND
120H  25/1800Z...DISSIPATED

$$
Forecaster Beven



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