The incident happened around 10:40 p.m. on Tuesday near the corner of Scott Street and Mallow, according to HPD.
Investigators with HPD said they believe the suspect shot toward the store from a grassy area nearby.
Two women in their mid-30s were standing in the parking lot when they were each shot in the arm, and another woman in a car nearby was shot in the hand, HPD said.
The third victim reportedly drove away from the scene before stopping on Vera Street, where she called for help and officers found her.
The women were taken to the hospital and are expected to be OK, officials said.
HPD said a bullet hit the convenience store and struck a cooler in the back area, but no one else inside the store was hurt.
"The investigation is ongoing to figure out who in the heck did this, but they snuck up in here and shot quite a few rounds toward that store," Lt. Wilkens with HPD said.
HPD said the suspect shot at least 30 rounds from the nearby area.
Investigators said they are still working to identify a suspect and motive.
Anyone with information regarding the incident is urged to contact the Houston Police Department or Crime Stoppers.