The storm, located about 390km off the southern tip of Baja California, is slowly continuing westward at 4.8km/h and expected to strengthen in the next day before weakening this weekend, according to the National Hurricane Center.
The maximum sustained winds were 193km/h as of Thursday afternoon. Rachel's swells are expected to generate life-threatening surf and rip-current conditions off Mexico's coast, the NHC warned.
Mexican authorities on Thursday said they remain on alert because of forecasts of very heavy rain in the states of Baja California Sur, Sinaloa, and Jalisco, and the possibility of landslides, rising river levels, overflowing rivers and flooding in low-lying areas.
The Pacific has seen an unusually busy hurricane season, which experts have attributed to El Niño, which has fuelled crippling droughts in Mexico and Central America and floods in other parts of the region.
In the Pacific, it has resulted in warmer waters and wind patterns that act as fodder for hurricanes.
Tropical Storm Nolo continued its northwest approach away from Hawaii on Thursday, though the National Weather Service said it could strengthen into a hurricane by the weekend.
Parts of northern Mexico were still reeling from floods and wider destruction left by Polo. Hundreds of people remained displaced or had their homes destroyed, and at least 13 municipalities remained flooded Thursday night, according to local authorities.
Areas in Texas, Nebraska, Missouri and Iowa were still under flood watch Thursday afternoon as storm remnants continued to batter the region, flooding streets and neighbourhoods and setting off water rescues.
