Roy Hodgson's side have been drawn alongside four-time World Cup winners Italy and two-time winners Uruguay in the groups, with Costa Rica also involved.
Forster, who was one of three goalkeepers named in the squad alongside Joe Hart and Ben Foster, acknowledges that it will be tricky for the team and also believes that the climate could play a part in proceedings.
"Italy and Uruguay are going to be very tough, but all the games in the group will be hard. With the climate as well it's not straightforward," Forster is quoted as saying by PA.
England's first match of the tournament comes against Italy on June 14.