Less than a week after a wildfire destroyed more than 100 homes and burned 4,100 acres, San Diego County is under a red flag warning.

Strong, gusty winds and low humidity are in the forecast until Friday, according to the National Weather Service.

The winds will increase during the day Thursday and are expected to peak Thursday night into Friday morning.

Northeast winds are expected to reach speeds of 20 to 30 mph with gusts up to 50 mph.

Julian could be gusting at near 40 around noon. Pine Valley could be higher than that, according to NBC 7 Meteorologist Jodi Kodesh.

“The corridors, the passes, the peaks in the mountains are going to be extremely gusty today,” Kodesh said. “Potential to see some isolated spots.”

The minimum relative humidity could dip into the single digits.

On the day of the Lilac Fire, the U.S. Forest Service put San Diego County under extreme Santa Ana wildfire threat. The same rating tool puts San Diego on a marginal threat level for Thursday and again for Sunday and Monday next week.

A marginal designation means new and existing fires will spread rapidly within the more wind prone areas.

Firefighters have the Lilac Fire almost surrounded as of Wednesday morning. The cause of the fire was under investigation.

In other parts of Southern California, a strong ridge of high pressure over the center section of the state along with an offshore flow is creating very dry conditions.

Fire weather warnings are in effect for Los Angeles and Ventura counties where firefighters are battling the Thomas Fire.

That fire threatens 18,000 homes. So far, 701 homes, two apartment complexes and 12 commercial structures have been destroyed.