Why rain changes the picture
Heavy or prolonged rain increases the amount of water around the foundation. If drainage cannot carry it away efficiently, pressure and seepage can increase at walls, joints, cracks, and lower points.
Look at where the water first appears
Water at a wall crack suggests a different path than water emerging from the perimeter joint or around a sump basin. See wall leaks and floor seepage.
Possible solution paths
Depending on the cause, solutions may include drainage correction, French drains, sump systems, crack repair, or broader basement waterproofing.