Roslyn is expected to be a hurricane when it makes landfall by Saturday night or Sunday morning, the NHC said in its latest report.
The storm, now some 180 miles (290 km) south-southwest of the Mexican port city Manzanillo, is predicted to follow the coast before turning inward near popular resort town Puerto Vallarta, an NHC map shows.
The slow-moving storm is recording maximum sustained winds near 70 mph (110 kph) with higher gusts, the NHC said.
A Category 1 hurricane packs winds of at least 74 miles per hour (119 kph). The NHC currently forecasts that Roslyn will reach 105 mph (169 kph) as it nears Puerto Vallarta, making it a Category 2 before it dissipates inland.
The NHC warned that preparations to protect life and property within the area under hurricane watch, from beach town Punta Perula in the state of Jalisco to San Blas in Nayarit, "should be rushed to completion."
In Jalisco state, the local government told people to avoid beaches and banned mountain all-terrain-vehicle tours over the weekend to avoid possible landslides.
The NHC also expects Roslyn to cause a dangerous storm surge, producing "significant coastal flooding" near and to the east of where the storm makes landfall, bringing with it "large, destructive waves."
The storm is expected to dump rain across southwestern Mexico, with parts of the states of Colima, Jalisco, Nayarit and Sinaloa seeing four to six inches (10-15 centimeters) of rain, with some areas seeing up to eight inches.
(Reporting by Kylie Madry; Editing by Sarah Morland and William Mallard)
