By Krystian Orlinski

GOLETA, Calif. (Reuters) - A blistering heat wave in Southern California this weekend along with strong winds could further fan a wildfire that has sent swirling flames close to ranches and triggered mandatory evacuations, officials said on Friday.

The so-called Sherpa Fire feeding on chaparral and grass about 20 miles (32 km) northwest of the affluent city of Santa Barbara tripled in size from 1,200 acres (486 hectares) on Thursday night to more than 4,000 acres (1,619 hectares) early on Friday, fire officials said.

With temperatures forecast to hit the triple digits in coming days and winds picking up, officials said the blaze, in a largely rural area, was a harbinger of heightened fire risks for all of Southern California.

"We're here at the beginning of June and we're seeing very active fires very similar to behavior that we would typically see in the fall," said Daniel Berlant, a spokesman for the Cal-Fire firefighting agency.

The Sherpa Fire has not destroyed any homes or caused injuries, said Kerry Bierman, a spokeswoman for the joint operations center fighting the fire. But it has generated "fire tornadoes" of swirling flames and threatened at least 270 structures, leading hundreds of people to evacuate ranches and other homes in the area, officials said.

It also forced authorities to declare an emergency for Santa Barbara County and periodically close a stretch of the 101 Freeway. The highway near the coast stands as a barrier for a blaze that has been driven by winds down steep hills toward the Pacific Ocean, which occasionally is the final destination for wind-driven fires in this coastal part of the state.

The fire may eventually jump the highway, Berlant warned.

More than 1,200 firefighters were battling the fire which was only 5 percent contained, according to tracking website Investigators are seeking to determine what sparked it on Wednesday in Los Padres National Forest.

Meanwhile, the heat wave arriving in the Southwest on Sunday is expected to pose problems for people far beyond the fire lines.

Temperatures will spike in the southern parts of Arizona, Nevada and California, with some areas topping off at 120 degrees Fahrenheit (49 degrees Celsius), according to a National Weather Service advisory warning of potentially fatal cases of heat-related illness.

In New Mexico, which is not under the heat wave warning, communities were on edge after a fire in the central part of the state destroyed 24 homes near the small community of Chilili earlier this week, officials said.

The so-called Dog Head Fire has burned more than 16,000 acres (6,475 hectares) of timber and logging zones in three days and forced hundreds of people to evacuate, officials said.

(Additional reporting by Brendan O'Brien in Milwaukee and Alex Dobuzinskis, Writing by Alex Dobuzinskis; Editing by Bernadette Baum and Diane Craft)