"Additional weakening is forecast", the Miami-based agency said, with Rosa expected to become a tropical storm by early Monday as it approaches central and northern Baja California, which adjoins the USA state of California.
Hurricane Rosa was downgraded from Category 4 to 3 on Friday and is approaching the Southwest off the coast of Mexico.
Orange County may see seas up to 8 feet while surf could reach 5 feet along San Diego County.
Hurricane Rosa is forecast to bring heavy rain to northwest Mexico and parts of southwest America, prompting storm and flood warnings for areas in its path.
Rosa is expected to make landfall Monday as a tropical storm, then continue moving northeast, soaking the southwestern United States.
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Hurricane Rosa is shown from a National Oceanic and Atmospheric (NOAA) GOES East satelite over the eastern Pacific Ocean on September 27, 2018, in this image provided September 28, 2018.
"We are going to have a whole bunch of rain and it's. not the kind of thunderstorm rain that (is) associated with the monsoon (season)", Cerveny said.
"Coastal areas are expected to received 0.25" to 0.50" of rain Tuesday into Wednesday, said Brandt Maxwell, a weather service forecaster.
Kirk had maximum sustained winds of 40 mph and was located about 270 miles south-southeast of Puerto Rico. The storm is expected to become a tropical depression Friday night and degenerate into a low pressure trough by late Saturday.