The temperature is blistering hot during the summer June, July, August, September. (gets to 50+°C during July and August). Winter (December to February) temperature is about 12-18°C then. A wetsuit 2/3mm usually works well in the winter.
From Kuwait City drive south along the coast (about 100km). Follow signs to Mina Said (Suüd). Pass the power plant and access the beach with your 4x4 to the South of it. If you don't have a 4x4 you need to walk a bit longer.