The Los Angeles County Fire Department has ramped up staffing Thursday in response to increased fire danger caused by gusty winds and extremely warm temperatures.

There is an “extreme” danger of a fire starting in counties from Los Angeles to Santa Barbara on Thursday and Friday, the National Weather Service said.

The danger is so high because of a “combination of moderate to strong Santa Ana winds, hot temperatures, very low humidities and unusually dry fuels,” the service said in a statement Thursday morning.

Mountains and valleys across L.A. and Ventura counties are under a red flag warning through Friday night, with humidity expected to be extremely low and hot winds blasting north across the region at speeds upward of 40 mph in the valleys and coasts and 70 mph on mountaintops.

The poor weather is fanning a fire in Riverside County, where firefighters have been battling flames near Banning since Wednesday afternoon.

The National Weather Service said temperatures in Los Angeles are expected to peak at 89 Thursday and climb to 92 on Friday. Temperatures in the San Fernando Valley and inland could hit triple digits.

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Joseph.serna@latimes.com

@josephserna