Flood watches are in effect for parts of southern California and western Arizona.
Kay is expected to stay at hurricane strength until it’s about 250 miles from San Diego — something only four other storms have done since 1950, according to the National Weather Service — before weakening into a hurricane. moving to the west coast of the United States.
But the storm doesn’t have to be strong “for this to be a major concern for Southern California,” said Brandt Maxwell, a National Weather Service meteorologist in San Diego.
Kay is expected to track parallel to the Baja California Peninsula through Friday, pushing what could be a record amount of moisture into Southern California and Arizona. Then, just before the US-Mexico border, it will turn west – away from the coast – as it makes the closest pass to Southern California for a hurricane since Hurricane Nora in 1997.
Winds could blow in excess of 60 mph as the system interacts with the mountainous terrain in Southern California. And these winds will come from the east, which means they will have a warming effect on coastal cities; as the air descends the mountains, it is compressed and its temperature increases.
“It happened in 1984 when a Category 1 Hurricane Marie well southwest of San Diego County forced temperatures to reach 100 in San Diego,” Maxwell said.
Lows could stay in the 80s overnight Thursday into Friday morning, making sleep uncomfortable, especially for those without air conditioning.
Then the unrelenting heat will “end abruptly and unusually” on Friday evening, the Los Angeles Weather Service announced, as cloud cover and precipitation from the tropical system shifts, dramatically reducing temperatures but creating new hazards: heavy rain and a threat of flash flooding.
A year of rain in parts of Southern California
“Confidence remains high for a significant rainfall event in this region,” the Center for Weather Forecasting said Thursday morning. Models suggest humidity over this normally dry area will be well above the 99th percentile for this time of year before the weekend.
Even though precipitation is desperately needed in parched Southern California, such an amount of rain in a short period of time can cause streams and rivers to rise rapidly.
“It’s never a good thing to have too much rain all at once, an all-too-common trait among slow-moving tropical storms,” the forecast center said. “So the potential for flash flooding is also increasing rapidly.”
Rainfall of 2 to 4 inches, up to about 6 inches, is expected throughout the mountainous terrain of Southern California, especially on the eastern slopes.
A moderate risk of excessive precipitation warning – level 3 of 4 – is in effect Friday over parts of southern California and extreme southwestern Arizona, with a slight risk – level 2 of 4 – in force by Saturday over southern California, western Arizona and extreme southern Nevada.
The National Weather Service forecast 2 to 4 inches of rain over 36 hours Friday and Saturday at Imperial County Airport in southeastern California; the place receives an average of 2.38 inches of rain each year. If Imperial receives more than 3 inches of rain, this month would be its wettest September, breaking a record set in 1976.
In Palm Springs, Calif., 2 to 4 inches are forecast through the weekend, pushing toward the typical annual rainfall count of 4.61 inches. Three inches in Palm Springs would put this month among the three wettest Septembers in the city and make it the wettest since 1976, when it hit 4.17 inches; its average rainfall in September is 0.24 inches.
Yuma could see 1.5 inches of rain over the weekend, which would make September the wettest September since 2009. The city’s average September rainfall is 0.68 inches.