Another blast of Santa Ana winds Thursday prompted San Diego Gas & Electric to cut off electricity to thousands of residents in another of a wave of power outages that have continued off and on for two weeks. As of 4 p.m. Thursday, nearly 17,000 SDG&E customers living mostly in rural and backcountry communities had circuits de-energized to help prevent high winds from causing power lines to fall to the ground and potentially igniting a wildfire. Another 67,000 customers may potentially lose power if conditions worsen. SDG&E’s weather center reported gusts of 89 miles per hour at Sill Hill in the Cuyamaca Mountains at 9:15 a.m. and 71 mph in the Rancho Heights neighborhood near Pala. A red flag warning issued by the National Weather Service has been extended for mountains and valleys in San Diego until 10 a.m. Friday. High winds even suspended play for 90 minutes Thursday afternoon during the second round of the Farmers Insurance Open, the annual PGA golf tournament at Torrey Pines. TV coverage showed pins on the greens bending almost sideways from the gusts. Forecasters expect the winds to taper by Friday and a low-pressure system may drop a quarter-inch of rain at or near the coast and a half-inch to a full inch in the mountains over the weekend, offering at least some relief to bone-dry conditions on the ground. The San Diego International Airport has recorded only 0.16 inches of precipitation since Oct. 1, when the rainy season began — making in the driest rainy season in the city since 1850. In many areas, the lack of rain has turned grass, chaparral and vegetation to tinder. Emergency crews on the ground and in the air have fought back a string of fires in the San Diego area — the most recent coming Wednesday in Rancho Bernardo when some residents were forced to temporarily leave their homes due to a brush fire that was contained to seven acres before it was doused. Since Jan. 8, one wave after another of fierce Santa Anas have blown through Southern California. Thus far, the San Diego area has escaped the devastation seen in the Los Angeles areas by wind-whipped blazes that leveled homes and forced evacuations. Union-Tribune staff reporters Teri Figueroa, Karen Kucher and Gary Robbins contributed to this story.