Manuel was churning along in the Pacific with the northern eyewall near the coast, the National Hurricane Center in Miami said in its 8 p.m. PDT advisory.
The hurricane was about 5 miles west of Altata, Mexico, and 105 miles southeast of Los Mochis, moving north at 3 miles per hour.
Maximum sustained winds were 75 mph with higher gusts.
A hurricane warning was in effect from La Cruz to Topolobampo. A tropical storm warning was in effect for Mazatlan to La Cruz, and a tropical storm watch for Cabo San Lucas to San Evaristo.
Manuel was expected to track north through early Thursday. The center will be near or over the west-central coast of Mexico Wednesday evening.
Hurricane-force winds extended 20 miles from the center, though some strengthening could occur before landfall.
Manuel was expected to produce 5-10 inches of rain over Sinaloa state with localized amounts of up to 15 inches possible, bringing the potential for life-threatening flash floods and mudslides.
A storm surge of 2-4 feet also could bring large, destructive waves.
Meanwhile, Tropical Storm Humberto weakened to a tropical depression as it turned north in the Atlantic Ocean well away from the Azores.
Humberto, with maximum sustained winds of 35 mph, was about 1,000 miles west-southwest of the Azores, moving north at 9 mph, the hurricane center said in its 11 p.m. Atlantic Standard Time advisory.
No coastal watches or warnings were in effect.
Humberto was forecast to turn to the north-northeast with an increase in forward speed Thursday.
The hurricane center said the storm was poorly organized.