A weekend heatwave with a drop in humidity could create hazards as firefighters work to contain what remains of the three major wildfire complexes in the Bay Area.

The fires, which were sparked by lightning strikes on August 16 and 17, are burning through their third week in parts of seven Bay Area counties, and as of Friday morning, containment on the two largest fires has topped 80 percent.

The SCU Lightning Complex is now 82-percent contained, having burned 396,624 acres; and the LNU Lightning Complex is 87-percent contained, having burned 375,209 acres. The Sonoma County portion of the LNU Complex, the Walbridge Fire, is now 93-percent contained.

"Dry and hot weather is predicted and southwest winds are expected today in the area," Cal Fire says in a morning update, regarding the LNU Complex. "Interior islands deep within the fire's perimeter may occasionally flare up."

As ABC 7 reports, firefighters working to fully contain the LNU Complex said Thursday that they are racing to get as much done as possible before this weekend's weather potentially creates prime conditions for the remaining flames to grow.

"These next 12 to 24 hours [are] very crucial for us," said spokesperson Captain Jesse Gomez, speaking to ABC 7.

The CZU Lightning Complex has burned over 86,500 acres in San Mateo and Santa Cruz counties, and it is only 56-percent contained as of Friday morning.

"The fire continued to smolder and creep through deep portions of duff overnight," Cal Fire said in a Friday update. ("Duff" refers to the layers of pine needles and debris that sit atop the soil in forests.) "Fire activity remained minimal as firefighters continued to build and reinforce containment lines."

Damage assessments are now complete or nearly complete on all the fires, and in total, 3,112 structures were destroyed by flames.

And after days of very slow progress, the Woodward Fire in western Marin County has reached 71-percent containment. The fire has burned 4,704 acres in and around Point Reyes National Seashore, and it continues to produce smoke that has been blanketing Marin County in recent days, as the Marin Independent Journal reports.

Photo: Cal Fire CZU/Twitter