Jessica Barrymore, half sister of actress Drew Barrymore, was found dead on Tuesday in her car in south San Diego County area, according to the San Diego County Medical Examiner's Office.

ABC News reported that Barrymore died the day before her birthday. The actress' half sibling would have turned 48 on Wednesday.

Sister Drew Barrymore had only met Jessica for a short time, but both were daughters of actor John Barrymore. The E.T. actress release a statement extending her condolences to the rest of her half sister's family.

"Although I only met her briefly, I wish her and her loved ones as much peace as possible," Barrymore said in the statement. "I'm so incredibly sorry for their loss.

After she was found in her car, the fire department confirmed she had died. A cause of death has not yet been determined.

The New York Daily news reports that initial suspicions are the Jessica Barrymore died of a drug overdose.

"She appeared to be sleeping in her vehicle, partially blocking a driveway. We went out to check her welfare, and she was cold to the touch, obviously deceased," National City Police Lt. Robert Rounds said.

Rounds said police "froze the scene" and took custody of Barrymore's Toyota Camry and "all its contents" waiting on a cause of death from the San Diego County Medical Examiner.

"She apparently lived out of the area in northern San Diego County, so she was out of place on that block," he said.

Marta Lopez said that she found Barrymore in her car when she was heading to work on Tuesday morning. Lopez told reporters that Barrymore was leaned back in her seat with a drink between her legs and was unresponsive. Several white pills also were scattered around the car.

"I called, ‘Are you Okay? You need some help?'" Lopez said.

An autopsy was scheduled for Wednesday, which will reveal the cause of death.