Roslyn prompted the issuance of hurricane and tropical storm watches and warnings by the Mexican government for Western Mexico.

The convection within it gradually increased over the next couple of days, and an area of low pressure formed south of the southern coast of Mexico on October 19.

Its circulation became better-defined later that day, resulting in the formation of a tropical depression by 00:00 UTC on October 20, about 140 mi (220 km) south-southwest of Acapulco, Guerrero.

The storm steadily strengthened into the following day, tracking west-northwestward over warm near–85 °F (30 °C) waters and experiencing only minimal wind shear.

[1] By 15:00 UTC on October 21, a central dense overcast with overshooting tops formed near the storm's center, along with a partial eyewall beneath it.

[3] Roslyn became a hurricane eight hours later about 185 mi (295 km) south-southwest of Manzanillo, Colima, and proceeded to rapidly intensify.

[1] Roslyn became a Category 3 major hurricane early on October 22, as a well-defined eye became visible in infrared satellite imagery, with cloud tops in the surrounding central dense overcast temperatures as cold as −110 °F (−80 °C).

[5][6] Increasing southwesterly vertical wind shear and interaction with the mountainous terrain of Mexico caused the system to rapidly weaken,[7] becoming a tropical storm later in the day.

[8] In anticipation of Roslyn, the government of Mexico issued a hurricane warning for the coast extending from Playa Perula south of Cabo Corrientes, Jalisco, north to Escuinapa Municipality, Sinaloa, and for Las Islas Marias.