This satellite image made available by NOAA shows Hurricane Kay off the Pacific coast of Mexico, early Wednesday, Sept. 7, 2022. Kay's maximum sustained winds rose to 100 mph Wednesday, with forecasters saying it could brush the mid portion of the peninsula this week.
The California heat wave that brought punishing temperatures to the San Francisco Bay Area is finally coming to a close. Friday marks the start of a cool down with the fog returning and remnants of Hurricane Kay reaching the region this weekend.
Afternoon highs in the Bay Area on Friday will be 5 to 10 degrees cooler than they were on Thursday and 15 to 20 degrees less than they were at the peak of the heat wave on Tuesday, the National Weather Service said. Livermore soared to 116 degrees Tuesday and is forecast to reach 102 on Friday and 88 on Saturday. San Francisco hit 98 on Tuesday and is expected to reach 76 on Friday and 74 on Saturday.
"It should definitely feel like a big relief," said Sarah McCorkle, a forecaster with the weather service's Monterey office said.
The cooler weather comes as a trough of low pressure to the north and remnants of Hurricane Kay to the south break down the high pressure-ridge that brought the intense stretch of warming.
"We have two low pressure systems squeezing us to the north and the south and that's helping weaken the high pressure," McCorkle said.
The waning high pressure has opened the door for coastal fog, and McCorkle said the marine layer that has been only a few hundred feet thick in recent days was up to 1,000-to-1,500-feet deep off the coast of Monterey this morning.
"The marine layer has been deepening so people in inland valleys and at higher elevations should feel cooler as well," she said. "We're looking at fog returning to San Francisco tomorrow."
A man covers himself from the rain with an umbrella in poor condition after heavy rains in Mexico City, due to the passage of Hurricane Kay in the State of Baja California in the Mexican Republic, which will maintain the forecast of rain in several states of the country.
Tropical Storm Kay reached landfall in Mexico on Thursday morning as a hurricane, and last night, it was downgraded to a tropical storm. The storm is projected to move north over the Pacific Ocean, parallel to the California coast, with its eastern edge brushing Southern California Friday and Saturday, bringing significant rain, up to 2.5 inches to the wettest locations.
Remnants of the storm will push into Northern California Saturday into Sunday. Confidence is high that the system could deliver rain and wet thunderstorms to the southern parts of Monterey and San Benito Counties on Saturday night and Sunday morning. "There's anywhere from a 20% to 40% chance of rain," McCorkle said.
Parts of Southern California woke up to light rain Thursday morning during the ongoing heatwave in Los Angeles on September 8, 2022. According to Ryan Kittell a meteorologist with the National Weather Service in Oxnard, the rainfall has been splattered over the Los Angeles valley and coastal areas a rain preview from Hurricane Kay.
McCorkle said the chance for rain in the nine-county Bay Area is much less. "There is a chance Saturday evening into Sunday morning that the Bay Area could see some scattered showers," she said. "I'd put them at a 10% chance."
Even if the storm doesn't bring wetting rain, it will deliver some clouds that will help increase humidity levels and decrease wildfire risk.
Amy Graff is the news editor for SFGATE. She was born and raised in the Bay Area and got her start in news at the Daily Californian newspaper at UC Berkeley where she majored in English literature. She has been with SFGATE for more than 10 years. You can email her at agraff@sfgate.com.