Tropical Storm Kay, first to affect Southern California in 25 years, could raise temps in already-hot state

Tropical Storm Kay isn’t expected to directly hit California, but strong winds could make it feel hotter in parts of the state, where millions remained under excessive heat warnings Friday. 

Forecasters expect parts Southern California to experience flash and urban flooding Friday, even as the National Hurricane Center's model showed Kay spinning away from the coast. Kay's maximum sustained winds dropped to 45 mph Friday as it brushed by Southern California, according to the NHC.

Winds from the storm can raise temperatures before rainfall brings them back down, experts said. 

The tropical storm, the first to impact Southern California since 1997, will likely weaken by Saturday, said AccuWeather senior meteorologist Alan Reppert. Kay made landfall Thursday in Baja California, Mexico, as a Category 1 hurricane. The storm killed three people in Guerrero, Mexico, Reuters reported.

Here's what to know about the tropical storm's track.

How will Kay impact California?

Widespread rain moved into San Diego County Friday morning, and winds of 80 to 90 mph were reported in the area's mountain slopes, according to the National Weather Service in San Diego.

The Los Angeles basin could be drenched with an inch or more of rainfall, Reppert said, and regions farther east could see far more than that. Half-a-foot of rain is possible in Riverside and San Diego County mountains and deserts, the NWS says.

A northern cold front over the Rockies will usher in cooler conditions in California over the weekend and next several days, according to Reppert.

“It will be cooling off after Kay dissipates and moves away with the rainfall,” he said.

The National Hurricane Center's cone shows the projected path of Tropical Storm Kay off the coast of Mexico and California Friday.

Will the storm make it hotter in parts of California?

Over 28 million Californians were under an excessive heat warning Friday, and winds from Kay were expected to warm up some areas even further, Reppert said. 

'INTO THE TRIPLE DIGITS':Heat wave prompts another flex alert in California; Hurricane Kay to bring weekend rain

Temperatures in downtown Los Angeles reached 89 degrees by 9 a.m., he said, and the National Weather Service in San Diego reported temperatures in the 80s Thursday morning as rain from Kay began.

“With the sinking air around the storm and wind directions coming off the land instead of off the water, especially in coastal areas, it’s going to get quite warm across the state and remain warm until we see that precipitation move in,” Reppert said. 

Why would Kay's winds heat up California? 

When air moves down a mountain slope, like with Santa Ana winds moving toward California’s coast, it warms up through compression, explained Dr. Kim Wood, associate geosciences professor at Mississippi State University.

THERE'S STILL HOPE, EXPERTS SAY:Dramatic increase in deadly US heat waves now likely inevitable

TOP WEATHER-RELATED THREAT:Why ranking heat waves could save lives

“For a case like this, you may notice if you look at a satellite loop of Kay that it's spinning counterclockwise, and the direction of the flow currently moving over California is from east to west from inland to the coast,” Wood told USA TODAY. “So it could be inducing those downslope winds, which would cause warming.”

What makes Kay’s Pacific track unique? 

Southern California hasn’t been affected by a tropical cyclone since Hurricane Nora in 1997, which Wood said directly impacted the state — meaning the storm’s center moved across land.

Wood called Kay’s track in the eastern North Pacific “a bit unusual.” No other tropical storm has been in Kay’s location off the coast of Baja California, Mexico, and Southern California since 1988, when the National Hurricane Center took responsibility for the basin, she tweeted Friday.

Wood added “only a handful” of tropical cyclones have been near that area, if pre-1988 tracks are included.