The England cap joins Saints on a month's loan and West Ham's goalkeeping coach Ludek Miklosko said: "Richard is a fantastic lad and we thought he just needs to play. There was an opportunity for him to get some games and I just wish him luck.
"Hopefully he will do well. That's what he needs. He has definitely helped Robert this season. He has pushed him hard and is a great goalkeeper. He has a great attitude."