“Confidence is rapidly increasing for a significant rainfall event across Southern California, Arizona, and eventually central California and Nevada into Saturday,” the National Weather Service wrote in an online discussion Wednesday.
The heat and drought relief offered by such rain would be beneficial in this exceptionally dry region. However, there is a serious risk of flooding as runoff affects the parched terrain.
“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. “Thus, the flash flood potential is summarily also rapidly increasing.”
Forecasters, however, stress that there is large uncertainty in exactly how much rain will fall and where.
A Category 2 hurricane with 100 mph winds, Kay is churning in the Pacific Ocean southwest of the tip of Baja California. It is expected to move essentially parallel to the Mexican peninsula over the next couple of days.
The National Hurricane Center calls for Kay to strengthen slightly Wednesday before starting to weaken Thursday as it gets closer to a possible landfall in Mexico. Hurricane warnings have been hoisted for the west-central coast of Baja California, where the storm is supposed to be closest to the coast, while tropical storm warnings have been issued farther south.
Parts of Baja California could see up to 15 inches of rain from Kay, as well as a destructive ocean surge and hurricane-force winds. Flooding rains from Kay have already killed three people in Baja California, according to local reports.
Winds from Kay are expected to impact nearly all of Baja California — even on the Gulf of California side. Kay is a large hurricane with tropical-storm-force winds (39-plus mph) extending up to 230 miles from its center.
Potential impacts in Southern California
Kay’s size makes it probable that the storm will, in fact, bring notable impacts to Southern California, Arizona and Nevada even though the Hurricane Center has the storm starting to bend away from the California coastline and its offshore islands Friday.
By Thursday, clouds from Kay will begin spreading into the Southwest United States, helping bring relief from the heat. “The huge cloud shield of Kay will very effectively end the ongoing heat wave across the area,” the Weather Service wrote.
A few outer bands of Kay could stray into far-southern parts of California as early as Thursday, according to the Weather Service forecast office in San Diego.
Moisture from Kay is forecast to spread over the region in earnest Friday, bringing with it the potential for rainfall from San Diego to Phoenix, with downpours possible as far north as Las Vegas.
The Weather Service has placed a large swath of Southern California in the slight- to moderate-risk zone for flash flooding from Friday to Saturday morning. It cautioned that the risk could be upgraded to high if model simulations converge on multiple inches of rainfall.
There remains uncertainty as to exactly how much rain will fall and where, but the counterclockwise flow around the storm will steer winds from the east over much of the Southwest. This steering flow means the heaviest rainfall will probably concentrate along the eastern slopes of Southern California’s mountains.
“The most susceptible areas for flash flooding will be in slot canyons, burn scars and urbanized areas,” the Weather Service wrote. “The Peninsular Ranges of Southern California, being the mountains furthest southwest and therefore closest to the ocean and the center of Kay, will get the brunt of the associated rainfall.”
The latest rainfall projections through the weekend from the moisture from tropical cyclone Kay. There remains uncertainty on the timing and amounts, but the greatest potential for heavier rainfall remains on the east slopes of the mountains. #cawx pic.twitter.com/9NLlyZCeBS
— NWS San Diego (@NWSSanDiego) September 7, 2022
Current rainfall projections suggest that areas closer to the coast, from San Diego to Los Angeles, should see about 0.5 to 1 inch of rain. The Weather Service wrote that if the storm track shifts closer to the coast, it would “mean more rainfall in the coastal cities, specifically San Diego and nearby suburbs, but could eventually spread north into Los Angeles on Saturday.”
Kay’s winds and rain are likely to also have an effect on California’s wildfire situation, which has worsened in recent days. Between Friday and Labor Day, four people were killed in two separate wildfires in the state.
If Kay tracks closer to the coast, more rainfall is likely in Southern California and Arizona, which will be helpful in denting the region’s drought and lowering the wildfire risk. But if Kay tracks farther offshore, it would decrease drought relief and an acute fire risk would remain.
Kay would not be the first tropical system to impact California, but such occurrences in the state are fairly rare. They typically originate from the remnants of tropical storms and hurricanes, as would be the case with Kay, rather than direct strikes.
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.
“Ocotillo, Calif. suffered catastrophic damage, with 70 to 80 percent of the town destroyed,” NASA wrote in a recap of the storm. “Twelve deaths were blamed on the storm in the United States.”
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.
The Atlantic is busy, but there are no U.S. landfall threats
The tropical Atlantic is bubbling with activity after a rare August with no named storms.
Danielle, a Category 1 hurricane, is dancing harmlessly in the Atlantic Ocean, and is expected to perform a loop-de-loop more than 600 miles to the northwest of the Azores before tracking toward Spain as a post-tropical cyclone.
Hurricane Earl, also a Category 1 storm, is expected to become the season’s first major hurricane, rated Category 3 or higher, late Thursday. The large storm is forecast to brush Bermuda, which is under a tropical storm warning because of the potential for strong winds and rough seas over the next 36 hours.
Two more systems have caught the eye of forecasters at the National Hurricane Center. A tropical wave to the west of the Cabo Verde islands has a 60 percent chance of developing into a tropical depression over the next 48 hours, while a strong tropical wave moving off the coast of Africa has a 30 percent chance of developing into a tropical system within the next five days.