SAN DIEGO -- As several large wildfires tore through parts of Los Angeles, Ventura and San Bernardino counties Wednesday, San Diego County remained under a red flag wildfire warning prompted by strong Santa Ana winds and near-negligible humidity levels, with the National Weather Service predicting wind gusts approaching 90 mph will begin Wednesday evening and continue into Thursday.
NWS forecasters extended the red flag warning -- signifying potentially "extreme" combustion hazards in local coastal, inland-valley and mountain communities -- until 6 p.m. Saturday. The warning had been set to expire late Thursday night.
Additionally, the federal agency lengthened an accompanying high-wind warning for the county's valleys and mountains by 24 hours, moving back its scheduled expiration to 4 p.m. Friday.
On Tuesday, U.S. Forest Service firefighters knocked down flames that scorched fewer than two acres in the Cleveland National Forest. That blaze was reportedly started by a lost hiker but was able to be contained unlike the Thomas Fire, which had scorched more than 55,000 acres and destroyed more than 150 structures in Ventura County as of Wednesday morning. Two fires in Los Angeles County had also scorched more than 16,000 acres as of Wednesday morning.
Locally, the most critical fire conditions will start Wednesday evening and continue into Thursday, with wind gusts expected to reach up to 90 mph, forecasters said.
On the upside, mild temperatures are expected to help mitigate the fire danger somewhat, though significant risk will remain due to the strong winds and humidity levels in the 5- to 15-percent range, the NWS advised. High temperatures Wednesday in San Diego County will be 74 to 79 degrees at the beaches and inland, 78 in the western valleys, 68 to 73 near the foothills and 57 to 66 in the mountains.
To prepare for the dicey conditions, both the San Diego Fire-Rescue Department and San Diego Gas & Electric beefed up staffing levels this week. The former agency put several extra strike teams -- equipped with 10 brush rigs, five engines, two water trucks and two helicopters -- on alert, while SDG&E officials staged field crews and contract firefighters in areas where winds are expected to be the strongest.
"Meteorologists at the National Weather Service have not seen models for a Santa Ana event like this in many years," San Diego Fire Chief Brian Fennessy said over the weekend. "We are being vigilant in up-staffing to protect San Diegans and their property. We ask that residents practice their evacuation plans and be prepared in case of a wildfire."
SDG&E -- which last week lost a ruling in relation to the 2007 wildfires the company was found responsible for starting -- said it may need to turn off power this week in certain areas "if weather conditions threaten the integrity of our system and create the possibility of an imminent emergency."
Several years of drought coupled with heavy rains last winter have led to significant fire fuel in the form of underbrush and grass, and a lack of recent rainfall coupled with frequent low humidity have dried out that extra fuel, making it ready to burn freely, according to firefighting officials.
The U.S. Forest Service Santa Ana Wildfire Threat Index, which categorizes Santa Ana winds based on anticipated fire potential as extreme, high, moderate, marginal or no rating, predicted that the danger would be extreme on Thursday and high on Friday. Wednesday, the index listed the threat as marginal.
On Thursday, with some local gusts possibly exceeding 90 mph, wildfires potentially will "have extreme growth, will burn very intensely and will be uncontrollable," according to the Forest Service.
Public safety officials and the weather service cautioned the public to "avoid activities that could spark a fire" and warned of the risks associated with high winds, including power outages and damaged or toppled trees or power lines.