SONOMA, Calif. – Wildfires already well on their way to becoming the deadliest and most destructive in California history could gain momentum Thursday and erase even the modest gains firefighters have made. Steady winds with gusts up to 45 mph with nearly non-existent humidity are expected to descend on the areas north of San Francisco where at least 23 people have died and at least 3,500 homes and businesses have been destroyed. “It’s going to continue to get worse before it gets better,” state fire Chief Ken Pimlott said Wednesday. Entire cities had evacuated in anticipation of the next wave, their streets empty, the only motion coming from ashes falling like snowflakes. They included Calistoga, the historic resort town of wine tastings and hot springs, whose 5,300 people are all under evacuation orders.