The storm will hit the SF Bay Area with rain and wind today. It will be more intense tomorrow

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Do you remember Typhoon Merbok? It quickly evolved into a hybrid of itself, becoming a mid-latitude cyclone off the Aleutian Islands in Alaska. This cyclone draws its energy from the temperature differences between the land and the sea, causing intense winds, rains and waves throughout the Bering Strait.

The cyclone will quickly spawn a cluster of tiny storms just off British Columbia waters. This group will be fed by the cyclone’s exhaust and will eventually become a single storm. This process will result in the next storm this weekend for California.

The sequence of events that weather models have been predicting for several days still holds true, but the timing has changed slightly, so some of the first winds and bands of rain moved into the Bay Area as early as Saturday after- midday.

Weather models signal that the initial winds for this storm will begin as its cold front blows just off the coast of Sonoma County, Santa Cruz and east of the Oakland Hills. This is important, as storms arriving in the Bay Area from the northwest tend to produce some of their heaviest rain showers along the Coast Ranges of Sonoma and San Mateo counties.

It’s full steam ahead

Winds will peak at around 20 to 25 mph in the Bay Area Saturday afternoon. They will also draw in moisture from the Pacific and begin to bring rain showers, starting with the Sonoma Coast.

After digging into gaps and passes in the Coast Ranges, the cold front will engulf parts of the Santa Cruz Mountains, East Bay Hills and possibly the Sacramento Valley by late Saturday night and Sunday morning. These showers will become more widespread and move across the peninsula as the cold front dips further into California.

As for the Santa Cruz coast, expect those 20-25 mph winds to remain confined to the beaches along Highway 1 and some of the mountain passes, like Highway 17, that feed the coast. . Once the rains start to fall on Saturday evening, there can be even more wind, reaching gusts of 30 to 35 mph above 1,500 feet and even sometimes stronger at some of the peaks like Loma Prieta in the mountains from Santa Cruz.

The North American weather model predicts a late Saturday to early Sunday onslaught of the storm’s first rain showers moving through the Bay Area.

Weather Pivot

Whenever it rains along some of our mountains and coastal passes there is always a risk of isolated landslides. Fortunately, these showers are dispersed over a long period of time, so the chances of them occurring remain low. Make sure to drive safely this weekend, especially if you plan to drive over remote passes in the mountains.

So despite the heaviest showers and rains only arriving on Sunday, the Bay Area can still expect to see a wide range of winds, light rain and even pockets of heavier rain bands on Saturday. throughout the day.

Breakdown of the weekend

• San Francisco: Brief bursts of clear skies are expected on Saturday morning before rain showers develop and land in the evening. Look for citywide daytime temperatures between 65 and 69 degrees this afternoon, with sustained winds of up to 20 mph before sunset.

If enough bands of rain move over downtown on Sunday, the city’s official weather station could flirt with the 2.02-inch rainfall record for September 18, set in 1959.

Be prepared for more widespread showers and slippery roads overnight.

• The Pacific coast: Cloudy skies and blustery winds of 15 to 20 mph will give way to heavier rain on Saturday afternoon. Look for showers to start around Pacifica and Half Moon Bay. These showers will eventually track south across the rest of the San Mateo County coast late Saturday evening and early Sunday morning.

Expect daytime temperatures on Saturday to be in the mid-60s and nighttime temperatures to dip into the 50s as heavier showers move in. Daytime temperatures will stay about the same on Sunday as heavier showers roar down the coast.

• North Bay: A partly cloudy start for the North Bay Highlands and the towns of Petaluma, Napa and Santa Rosa before bands of rain moved in from the Sonoma Coast on Saturday. Look for temperatures in the mid-70s on Saturday afternoon and winds of 15-20 mph as heavier bands of rain land in the evening.

Whether you are north or south of Novato, daytime temperatures on Saturday are expected to drop into the 60s and stay that way through Sunday as rain showers engulf the entire region. Look for even heavier bands of rain overnight and Sunday morning, with some of the highest rainfall totals likely to exceed 2 inches in the Marin Headlands and Sonoma Coast.

According to final precipitation totals for Sunday, Santa Rosa could approach its precipitation record of 2.82 inches for Sept. 18, set in 1959.

• East Bay: Saturday’s temperatures are expected to reach only the upper 60 degrees in Oakland and all cities along the Interstate 880 corridor. Look for winds off the bay and over the East Bay hills to pick up this afternoon, with gusts up to 25 mph possible as rain showers enter the corridor.

These winds and rains will eventually flow east of the Interstate 680 corridor into cities like Walnut Creek and Fairfield. Overnight, those winds and rains will be followed by the storm’s cold front as temperatures rise from low 70s during the day to 60s before midnight Sunday.

• South Bay and Santa Cruz: The storm will slowly approach the Santa Cruz coast on Saturday, with winds blowing 30 to 35 mph just off the coast as of noon. Weather models forecast winds of 25-30 mph closer to the Santa Cruz shoreline by mid-afternoon, while the Highway 17 corridor may look for sustained winds of 15-20 mph before sunset .

Bands of rain will begin rolling into Davenport and nearby communities along Highway 1 by mid-afternoon before eventually spreading to the southwest peaks of the Santa Cruz Mountains. Expect brief local bursts of heavy rain before midnight in the summits. The cold front from the storm will cause temperatures in the Santa Cruz and Santa Clara Valley to drop from the low 70s Saturday afternoon to the 60s by 4 p.m. to 6 p.m.

Some showers could arrive in San Jose and Palo Alto before Saturday’s close, but for now it looks like a bigger chance is confined to Sunday. Look for more widespread showers and similar daytime temperatures on Sunday.

g
erry Díaz (he/they) is an editorial meteorologist for the San Francisco Chronicle. Email: [email protected] Twitter @geravitywave

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