Cal Fire has issued an evacuation warning for rural unincorporated Tri-Valley generally south of Interstate 580 and east of Highway 84 due to fire danger with high winds and dry thunderstorms starting in the forecast starting overnight Sunday.

The warning excludes the cities of Pleasanton and Livermore, as well as some more-populated unincorporated areas such as Happy Valley and anything west of I-680 such as Castlewood, as of 7 p.m. Sunday.

No local evacuation order has been issued yet, but Cal Fire and Alameda County emergency officials urge residents to prepare themselves to evacuate if needed.

"This warning is being issued in advance of the weather event because of the remoteness of this area and the limited egress routes, which may be inaccessible should this fire spread as anticipated," Alameda County officials wrote in an AC Alert message just after 6:30 p.m. Saturday.

"For those with pets or livestock, as well as those with access and functional needs, you are encouraged to leave the area. All others should be prepared to leave if the situation worsens or if they perceive a fire threat," they added.

The Tri-Valley warning comes as the SCU Lightning Complex fires south of Sunol continue to grow generally to the south and east, but weather conditions between Sunday night and Monday afternoon could exacerbate the wildfire danger -- both for current fires and the threat of new ones.

The complex, which is a collection of 20 separate vegetation fires caused by lightning strikes Aug. 15-16, increased slightly to 343,965 acres with 10% containment as of 7 p.m. Sunday. The complex is raging in parts of Alameda, Contra Costa, Santa Clara, San Joaquin, Stanislaus and now Merced counties.

In response to a red flag warning amid difficult weather forecasts, Cal Fire issued a series of new evacuation warnings in eastern unincorporated Alameda County south of I-580, including much of the rural Tri-Valley.

In the Tri-Valley, the evacuation warning area includes south of I-580 in between Greenville Road and the San Joaquin County line to the Alameda/Santa Clara County lines; south of the Livermore city limits; south of Highway 84 in between Vineyard Avenue and I-680; south of I-680 to the fire perimeter; and the Alameda/Santa Clara County lines west of the Alameda/San Joaquin County lines to the Livermore city limits, to Highway 84 to I-680.

It also includes north of fire perimeter and the Alameda/Santa Clara county lines to Highway 84 to the Livermore city limits to I-580.

The warning zone does not include the incorporated cities of Livermore or Pleasanton, as well as some unincorporated areas in Pleasanton close to the city such as Happy Valley, Castlewood and Foothill Road. Additionally, the warning zone does not include anything north of I-580 such as Dublin or west of I-680 such as parts of Pleasanton.

The only evacuation orders for Alameda County are all of Mines Road south of mile marker 10 to the county line as well as Frank Raines Park and Del Puerto Canyon Road in that area.

Cal Fire added a new evacuation order in Alameda County early Sunday morning: south of Welch Creek Road to the fire perimeter and the Alameda/Santa Clara county lines; and east of Calaveras Road at Welch Creek Road to the fire perimeter.

There are also a series of evacuation orders in place for parts of Santa Clara and San Joaquin counties, as well as other evacuation warnings for parts of Alameda, San Joaquin, Stanislaus, Santa Clara and Merced counties.

The SCU Lightning Complex had caused no fatalities but resulted in injuries of two first-responders and two civilians as of Sunday night. Seventeen structures had been destroyed, and 20,065 other structures were under threat, according to Cal Fire.

More than 1,300 firefighters have been assigned to the SCU Lightning Complex.

Smoke and poor air quality has enveloped the Tri-Valley and most of the Bay Area as a result of the wildfires.

Earlier Saturday, the National Weather Services issued a red flag warning for much of the Bay Area from 5 a.m. Sunday to 5 p.m. Tuesday. Cal Fire officials urge residents to prepare for the possibility of evacuation orders or warnings prompted by existing or new vegetation fires amid the dry storms.

"The weather forecast for this weekend continues to be warm and dry. Remnants of Hurricane Genevieve will bring thunderstorms as early as Sunday," said Daniel Berlant, assistant deputy director for Cal Fire.

"The best chance for thunderstorms and dry lightning is forecasted for the overnight hours tonight (Sunday) and into Monday morning. There will then be another chance for more activity Monday afternoon. Any thunderstorms will bring the threat of new fire starts to the entire complex. Gusty outflow winds remain a concern for unpredictable fire spread and safety of firefighters," he added.

There are also fast-moving wildfires raging elsewhere in the Bay Area and Northern California, including Solano, Sonoma, Napa and Santa Cruz counties.

Statewide, there were nearly 12,000 lightning strikes and more than 585 new wildfires burning nearly one million acres since Aug. 12. Most have been controlled but nearly two-dozen major incidents remain aflame across many jurisdictions, according to Berlant.

"The recent spike in wildfire activity is an important reminder for residents to take steps to prevent sparking a wildfire. Having an evacuation plan, a supply kit, and important paperwork will make it easier when it is time to GO. Remember one less spark, means one less wildfire," he added.