(CNN) Golfball-size hail, floods and stranded drivers. This is what May in Houston is looking like.

More thunderstorms and showers hammered Houston early Saturday morning and were expected to last through midday, the National Weather Service said. There was a high risk of excessive rain in southern Louisiana and Mississippi through Saturday night.

With more heavy rain, there's potential for flash flooding in areas where the ground is already wet, according to the National Weather Service's Weather Prediction Center . There was a moderate risk of excessive flooding for southeastern Texas and parts of Louisiana on Saturday, the center said.

The Upper Texas Coast and the Gulf Coast of western Louisiana has received "tremendous rainfall" in the past week, "300-600% of normal rainfall in that time frame," the center said.

A MODERATE risk is in effect in our Day 1 Excessive Rainfall Outlook. More details: https://t.co/FQU5sblUHQ pic.twitter.com/qFKC1pOEgl — NWS WPC (@NWSWPC) May 11, 2019

The region has seen storms moving over the same location for hours at a time, which is known as training, CNN Meteorologist Derek Van Dam said.