BATON ROUGE, La.—Heavy rain kept pounding parts of Texas and Arkansas before moving over Louisiana on Wednesday, adding to the misery for people whose homes and cars were flooded by an earlier drenching. The prospect of more rain wasn’t welcome in southern Louisiana, where heavy downpours earlier this week swamped vehicles and closed a major interstate. Three people were killed and one was missing after driving into high water. Flood watches covered a large part of Texas and Arkansas and most of Louisiana on Wednesday. Parts of Oklahoma and Mississippi were also under flood watches. Up to 4 more inches of rain was possible through late Thursday near the coast in the hard-hit Lake Charles, Louisiana, area, the National Weather Service said. Lake Charles is still recovering from back-to-back hurricanes last fall and a deep freeze in February. Twelve to 15 inches of rain fell in parts of Lake Charles …