Eastern Pacific Basin Tropical Cyclones

Tropical Storm Roslyn Forecast Discussion


000
WTPZ44 KNHC 210839
TCDEP4

Tropical Storm Roslyn Discussion Number   6
NWS National Hurricane Center Miami FL       EP192022
400 AM CDT Fri Oct 21 2022

Roslyn's structure has evolved since the previous advisory.  A more 
distinct core of deep convection appears to be developing, and 
infrared satellite images have even shown hints of an eye feature 
during the past few hours.  An elongated convective band now 
extends around the northeastern and southeastern quadrants of the 
circulation.  Based on consensus Dvorak estimates of T3.5 from TAFB 
and SAB, and a CI number of 3.4 from the UW-CIMSS ADT, Roslyn is 
now estimated to have maximum winds of 55 kt.

Recent scatterometer data and conventional satellite images 
indicate that Roslyn's center is a bit to the northeast of where it 
was estimated to be last evening, and the initial motion is 
west-northwestward, or 300/6 kt.  The track forecast reasoning has 
not changed.  Roslyn is expected to recurve around the western edge 
of a mid-level area of high pressure that will migrate eastward 
across Mexico during the next couple of days.  In 2 to 3 days, 
Roslyn and its remnants are then expected to accelerate 
north-northeastward in the flow ahead of an approaching deep-layer 
mid-latitude trough.  With the exception of the UKMET model (which 
is a western outlier), there is very little cross-track spread 
among the other track models, and most of the differences are in 
the forward speeds after 36 hours.  The biggest change in this 
forecast package is that with the northeastward adjustment of 
Roslyn's center, the entire official track forecast has been 
shifted east of the previous prediction, and lies close to the 
updated TVCE and HCCA consensus aids.

If Roslyn is indeed developing a better-defined core, environmental 
conditions could support rapid intensification (RI).  The SHIPS RI 
indices are now showing a 50 to 60 percent chance of a 30-kt 
increase in intensity over the next 24 hours, and the HWRF, 
COAMPS-TC, and HCCA consensus aids are all showing RI.  RI is 
therefore now explicitly forecast, and Roslyn should reach 
hurricane strength later today.  In 36 to 48 hours, an increase in 
southwesterly shear could induce some weakening, but regardless, 
Roslyn is expected to reach the coast of west-central Mexico as a 
hurricane.  Rapid weakening is expected after landfall, and 
although the official forecast shows a remnant low over northern 
Mexico in 72 hours for continuity, Roslyn is likely to have 
dissipated by that time. 

Given the relocation of Roslyn's center and the updates to the 
forecast, hurricane and tropical storm warnings are now in effect 
for portions of the west-central coast of Mexico.  Hurricane 
watches have also been extended northward along the coast.


Key Messages:

1. Roslyn is forecast to be a hurricane when it passes near and 
makes landfall along the west-central coast of Mexico late Saturday 
and Sunday, accompanied by strong winds and a potentially dangerous 
storm surge.  A Hurricane Warning is now in effect for a portion of 
the west-central coast of Mexico and will likely be extended 
northward later today.

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  21/0900Z 16.2N 103.8W   55 KT  65 MPH
 12H  21/1800Z 16.6N 104.6W   70 KT  80 MPH
 24H  22/0600Z 17.4N 105.5W   85 KT 100 MPH
 36H  22/1800Z 18.7N 106.2W   95 KT 110 MPH
 48H  23/0600Z 20.5N 106.2W   95 KT 110 MPH
 60H  23/1800Z 23.0N 105.1W   70 KT  80 MPH...INLAND
 72H  24/0600Z 25.7N 103.3W   25 KT  30 MPH...POST-TROP/REMNT LOW
 96H  25/0600Z...DISSIPATED

$$
Forecaster Berg



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