Just before landfall , it weakened , but Carla was still a very strong and unusually large Category 4 hurricane when it touched the shore between Port O'Connor and Port Lavaca , Texas , on the 11th . Just before landfall , it weakened , but Carla was still a very strong and unusually large Category 4 hurricane at its landfall between Port O'Connor and Port Lavaca , Texas , on the 11th .