Where did my strays go after it rained?

I was feeding some stray cats in a parking lot. I think their "base" was the storm drain. I had been feeding them for about a week, same time every night and same spot. They knew to look for me. It rained for 2 days and I haven't seen them since. Where might they have gone? They were people friendly strays, a momma cat, and a young cat I think was her kitten.

This parking lot is next to a large open field. I don't know what happened to my kitties or where they would have gone during the rain or why they havent come back to be fed.