“Confidence remains high for a significant rainfall event across this region,” the National Weather Service said in an online discussion Thursday.
The storm’s remnants could also bring gusty winds and dangerous surf conditions to coastal areas of Southern California.
A Category 1 hurricane with 85 mph winds, Kay is expected to make landfall on the west-central coast of Baja California in Mexico Thursday evening. The storm is weakening and forecast to be downgraded to a tropical storm on Friday.
Blamed for at least three deaths over Baja California, Kay continues to be a major rain-producer.
The storm is projected to bring 6 to 10 inches of rain to much of the peninsula, with localized amounts of up to 15 inches. Near the coast, Kay is expected to whip up large waves and dangerous rip currents, with a damaging storm surge, or rise in ocean water above normally dry land, possible as well.
Tropical storm warnings have been hoisted for the entirety of Baja California’s coastline, even on its eastern side, which rests on the Gulf of California. This is because Kay is a large hurricane; tropical-storm-force winds (39-plus mph) extend up to 230 miles from its center, while hurricane-force winds (74-plus mph) extend 35 miles from the center.
Effects on the Southwest United States
Kay is expected to further weaken and bend away from the Mexican coast as it gets closer to bone-dry Southern California. Still, winds from the southwest will drag Kay’s moisture into the region, first bringing with it cloud cover that will help to end the prolonged, record-setting heat wave.
The hurricane’s remnants will also carry unusual amounts of moisture that could help ameliorate the ongoing drought across Southern California. Some thunderstorms associated with Kay have already started rumbling near Riverside, Calif., bringing isolated heavy rain and lightning.
Although the rain is needed, the National Weather Service is cautioning that Kay’s arrival will not be without its dangers.
“Despite those positives, it’s never a good thing to get too much rain all at once, a trait all too common among slow-moving tropical storms,” the Weather Service wrote.
Precipitable water, a measure of atmospheric moisture, is forecast to be over 2 inches across parts of Southern California by late Friday. That is five standard deviations above the norm for the region at this time of year, meaning it is very rare.
Flash flooding is most likely in narrow slot canyons, in urbanized areas like San Diego, Palm Springs, Calif., and Yuma, Ariz., and over burn scars, where fire has stripped away vegetation and water tends to rapidly run off rather than soaking into the ground.
Flood watches have been hoisted from central Southern California into western Arizona, and the Weather Service has placed a large swath of Southern California and an increasing portion of southwestern Arizona in the slight- to moderate-risk zone for flash flooding from Friday to Saturday morning.
Rainfall amounts of more than 2 inches are likely in the zone covered by the flood watch, with up to 4 or 5 inches possible on the east slopes of mountains, where winds from the east will intensify the precipitation.
Updated rainfall potential through Sunday from the moisture from tropical cyclone Kay. The greatest potential for heavy rainfall and flash flooding is for the east slopes of the mountains and adjacent deserts areas for Friday afternoon and night. #cawx pic.twitter.com/JzaWihbf2k
— NWS San Diego (@NWSSanDiego) September 8, 2022
In San Diego, an inch or less of rain is expected, mostly falling Friday into Saturday morning. But, being along the coast will bring a separate set of hazards. The Weather Service is warning of dangerous rip currents and an elevated surf of 3 to 6 feet, along with the possibility of gusty winds up to 40 miles per hour.
In Los Angeles, the Weather Service predicts 0.25 to 0.75 inches of rain, with 1 to 2 inches in the mountains to its east, mostly falling Friday night into Saturday.
Some beneficial rain could reach as far north as the southern San Joaquin Valley before precipitation gradually dissipates on Sunday.
While Kay won’t come close to making landfall in California, it will still bring strong winds on Friday that will enhance the local fire danger. Gusts on the Laguna Mountains east of San Diego could exceed 70 mph, which will help feed any blazes.
Thunderstorms could also bring dangerous cloud-to-ground lightning that could ignite wildfires in the region — though any downpours from Kay may help quash some of them.
Kay is not the first tropical system to affect California, but such occurrences in the state are fairly rare. They typically originate from the remnants of tropical storms and hurricanes, as is the case with Kay, rather than direct strikes.
No named system has ever made landfall in California, though an unnamed storm in 1939 crossed the coast around Long Beach, bringing tropical storm conditions.
California’s most notable encounter with a tropical system was probably in 1976 when Tropical Storm Kathleen, previously a hurricane over the ocean, entered south-central California from Mexico. Kathleen unleashed a maximum rainfall of nearly 15 inches, a state record. The storm caused severe damage in Ocotillo, Calif., and was blamed for 12 deaths in the United States.
Jason Samenow contributed to this report.