A flood warning is in effect for parts of Southern California and western Arizona.
Kay is expected to remain a hurricane until it’s about 250 miles from San Diego — something that has happened with only four other storms since 1950, according to the National Weather Service — and then weaken as it moves toward the U.S. west coast.
But the storm doesn’t need to be strong, “that’s going to be a major problem in Southern California,” said Brent Maxwell, a meteorologist with the National Weather Service in San Diego.
Kay is expected to parallel the Baja California peninsula on Friday, pushing potentially record moisture into Southern California and Arizona. Then just near the U.S.-Mexico border, it will turn west — away from the coast — as it is the closest hurricane to Southern California since Hurricane Nora in 1997.
Winds can exceed 60 mph as the system interacts with the mountains of Southern California. And those winds will come from the east, which means they will have a warming effect on coastal cities; as the air goes downhill, it compresses and warms up.
“This happened in 1984 when Category 1 Hurricane Mary in southwest San Diego County forced San Diego to 100 degrees,” Maxwell said.
Lows are likely to remain in the 80s Thursday night through Friday morning, making sleep uncomfortable, especially for those without air conditioning.
Temperatures will plummet as clouds and rain from the tropical system move in, but also bring new dangers: heavy rains and the threat of flash floods, the Los Angeles Weather Service said.
Annual rainfall in parts of Southern California
“Confidence remains high for a major rainfall event in the region,” the Weather Forecast Center said Thursday morning. Modelling suggests humidity in the normally dry region will be well above the 99th percentile heading into the weekend at this time of year.
While arid Southern California desperately needs rain, so much rain in the short term can cause creeks and rivers to rise rapidly.
“Too much rain at once is never a good thing, it’s all too common in slow-moving tropical storms,” the forecast center said. “As a result, flash flood potential is also increasing rapidly.”
Rainfall is expected to be 2 to 4 inches across the mountains of Southern California and could be as high as around 6 inches, especially on the eastern slopes.
A moderate rainfall risk warning (level 3 or 4) was in place for parts of Southern California and parts of southwestern Arizona on Friday, with a minor risk (level 2 of 4) in effect for more areas Saturday. Southern California, Western Arizona, and Southern Nevada.
The National Weather Service forecasts 2 to 4 inches of rain in 36 hours at the Empire County Airport in southeastern California on Friday and Saturday; the location averages 2.38 inches per year. If the Empire receives more than 3 inches of rain, this month will be the wettest September, breaking the record set in 1976.
In Palm Springs, California, 2 to 4 inches of rain are forecast throughout the weekend, heading towards a typical annual rainfall of 4.61 inches. Palm Springs’ 3 inches will make it the city’s top three wettest Septembers this month and make it its wettest month since 1976, when it was 4.17 inches; its September rainfall average is 0.24 inches.
Yuma could get 1.5 inches of rain over the weekend, making it the wettest September since 2009. The city’s average September rainfall is 0.68 inches.