Red-flag fire warnings issued

Weather forecasters have issued a red-flag warning for the mountains of Los Angeles and Ventura counties as a sharp warming trend has produced hot, dry and windy conditions across the region that are expected to last into the early part of the week.

“It’s already hot out there,” said Ryan Kittell of the National Weather Service. “We’re expecting temperatures to continue to climb.”

The heat wave is expected to last through Wednesday, forecasters said. The hot conditions on Saturday led the Los Angeles Fire Department to deploy additional firefighters to neighborhood stations serving brushy areas, according to a spokesman.

The blistering weather comes on the first weekend of fall, after a summer that was notably cooler than usual. It prompted the city of Los Angeles on Saturday to open cooling centers in the San Fernando Valley for residents who need relief.

Afternoon temperatures for Sunday and Monday were expected to be in the triple digits across inland areas. An offshore flow is expected to produce gusty northeast winds through and below passes and canyons in Ventura and Los Angeles counties. The strongest period of wind, forecasters say, will be Saturday night through Monday, with gusts reaching up to 30 mph.

The San Fernando and San Gabriel valleys are also under fire weather watch, Kittell said. Such a watch means that critical fire weather conditions are forecast, while a red-flag warning means weather conditions are already ideal for wild-land fire ignition.

The heat wave is the result of a strong ridge of high pressure that is building over Central and Southern California. A slight cooling trend will bring relief Wednesday as the high-pressure system moves eastward. Forecasters remind people to take precautions to prevent heat-related stress and illness.

Bill Patzert, a climatologist for the Jet Propulsion Laboratory in La Cañada-Flintridge, said the L.A. area hasn’t had substantial rainfall since the second week of April. With La Niña conditions building in the equatorial Pacific, where ocean temperatures are cooler than normal, the fall and winter could be drier than usual, Patzert said.

“Definitely the conditions are there right now for everyone to be on high fire alert,” he said, adding that the worst could be yet to come with the arrival of strong Santa Ana winds.

But Patzert pointed out that last year’s massive and destructive Station fire did not occur during a period of heavy winds.

“So you don’t really need strong winds for a strong fire,” he said. “And it’s really dry out there.”

ruben.vives@latimes.com