No injuries were reported after the incident occurred about midnight at the building located at 2120 West Main Street. Whether the rain was directly responsible for the collapse remained under investigation.
Firefighters responded to the scene and assessed the structure, which was left with a gaping hole on the rooftop near the back of the store. The Target location is not expected to open for business Thursday as cleanup and repairs continue.
The National Weather Service had issued a flood advisory for parts of Los Angeles County, including the San Gabriel Valley and coastal areas, that expired at 3:15 a.m. Friday.
Scattered showers are expected Friday morning in Southern California, but the region will then see some late afternoon sunshine amid cool conditions.
Los Angeles County on Friday will see showers in the morning, but an afternoon high of 65 is on tap with the sun emerging later in the day. Sunny conditions continue into the weekend.