Rare tropical storm brings flooding, strong winds to California

WEATHER NEWS: Rare tropical storm brings flooding, strong winds to California

Tropical Storm Kay unleashed strong winds and flooding rains in Southern California Friday in a rare instance of a tropical weather system affecting the region. Downpours that triggered flooding also moved over parts of western Arizona.

Howling winds first entered Southern California early Friday, with gusts as high as 109 mph clocked in the high terrain, where multiple trees and power lines have fallen.

Meanwhile, weather radar showed bands of rain progressing through Southern California during the course of Friday, soaking the zone from San Diego to Los Angeles and areas to their east. Through 6 p.m. local time Friday, San Diego had received 0.61 inches of rain, shattering its Sept. 9 record of 0.09 inches and 9th most of any September day.

In extreme south-central California, flash flood warnings affected eastern San Diego and western Imperial counties, where some areas received more than 3 inches. Flooded roads were reported in Ocotillo, a town devastated by flash flooding by Tropical Storm Kathleen in 1976. Rock slides were also reported in the region.

Kay, which was a Category 1 hurricane when it made landfall Thursday on Baja California in Mexico, weakened to a tropical storm early Friday but still generated strong winds and drew a surge of tropical moisture northward over Southern California, western Arizona and southern Nevada.

The rainfall will be beneficial over the drought-stricken region, but its intensity will result in substantial runoff, presenting a significant flood threat which played out in some areas Friday.

The National Hurricane Center wrote that flash, urban and small-stream flooding was probable in Southern California, especially in the mountains, and that such flooding could occur in southwest Arizona later in the day. On Friday evening multiple flash flood warnings were scattered in the zone just west of Tucsoon and Phoenix.

The strong winds associated with the storm are forecast to gradually ease by Saturday as the storm curls farther offshore and loses tropical characteristics.

Multiple locations in the mountains of San Diego County reported gusts between 70 and 100-plus mph early Friday while they reached 40 to 80 mph in inland valleys. Along the coast, gusts were 40 to 50 mph.

Effects from tropical systems in the Southwest are not unprecedented, but they are infrequent. Even though Kay will not make landfall in California, the wind and rain generated on the storm’s north and east flank will be substantial.

The National Weather Service has hoisted widespread flood watches for the region — from just east of San Diego to around Las Vegas, affecting nearly 15 million people.

In the interior of far-southern California, a general 2 to 4 inches of rain is predicted, with isolated totals of 6 to 8 inches possible. The highest totals are most probable along the east-facing slopes of the Laguna Mountains east of San Diego.

In the mountains, flooding rains may lead to “dangerous debris flows near burn scars, landslides, rapidly flowing streams of runoff, and flooded/washed away roads,” the Weather Service wrote.

Precipitable water, a measure of atmospheric moisture, is forecast to be 2 to 2.25 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.

Amounts are forecast to be lower near the coast.

In San Diego, an inch or less of rain is expected, mostly falling Friday into Saturday morning.

In Los Angeles, the Weather Service is predicting 0.25 inches of rain at the coast and progressively more inland, with 1 to 2 inches in the mountains to its east. Most is expected to fall Friday night into Saturday. A flood watch has been issued for the mountains.

Southwest Arizona is set to pick up 1 to 2 inches of rain, with isolated 3-inch amounts, with the latest forecast increasing the flooding risk across Arizona and southern Nevada.

Precipitable water is forecast to be around 1.5 inches in the Mojave Desert and near Las Vegas, approaching all-time records for the area, according to the National Weather Service. Saturday brings the highest chance of downpours to Las Vegas, which twice saw water pouring into casinos during floods in July and August.

Flood watches extend as far north into California as Death Valley, which flooded in August when parts of the national park picked up roughly 75 percent of its yearly rainfall in a day.

Death Valley is sizzling weeks after record rainiest day

Rainfall is expected to continue in the Southwest on Saturday but will become less organized. Still, heavy showers and thunderstorms are possible considering the high amount of moisture available, creating a flood risk falling on terrain saturated by Friday’s rains.

Some beneficial rain could reach as far north as the southern San Joaquin Valley before precipitation gradually dissipates on Sunday.

Kay also brings with it strong winds that are triggering an unusually blustery day in San Diego and its nearby mountains.

At the coast, 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 mph.

A high wind warning has been issued for the San Diego area, stretching as far north as Riverside, Calif. The warning, which runs until midnight local time, says that east winds of 20 to 40 mph are expected, with occasional gust to 60 mph.

The winds may be strong enough to down trees and power lines, especially farther east toward the mountains. The strong downsloping breeze has also kept temperatures in the San Diego area warm, and an excessive heat warning remains active for the city and surrounding areas.

Gusts on the Laguna Mountains east of San Diego could exceed 70 mph, which could help fuel any active blazes or blazes sparked by downed power lines or by cloud-to-ground lightning in thunderstorms associated with Kay’s remnants — though any downpours from Kay may help quash active fires, too.

Past tropical systems to affect California

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 and was blamed for 12 deaths in the United States.

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