"I was here a year ago and it was hotter then. Even so, the humidity is so high, it will affect the match and that is the reason we tried to get the players to be as fit as possible," Van Gaal said at a news conference at the Castelao arena ahead of the match on Sunday.
"I'm quite conscious that it will also affect the Mexican team and I know they're much more used to it than we are."
Temperatures in Fortaleza have been hovering between 25-30 degrees Celsius the past several weeks, compared to lower temperatures in Rio de Janeiro, where the Dutch team has been practicing, and Sao Paulo and Porto Alegre, where it played its two most recent matches.
"Of course it's hot, it's very hot. It's a lot hotter than in Rio and the other cities that we played," midfielder Leroy Fer said at the news conference. "But the other teams are also affected. We feel we are well prepared."
Fer will sit out the match against Mexico, Van Gaal added, while Bruno Martins Indi is still recovering and will stay on the bench as a potential substitute.
"You don't really know when an injury is done and over with. He trained yesterday, 11 against 11, but that doesn't really mean he can play in these extreme conditions," Van Gaal said of the Feyenoord defender. "But he can be a substitute. He will be on the bench."
Mexico and Netherlands will both practice for the match away from the Castelao arena in a bid to preserve the pitch, which "is not that good," the Dutch coach added.
Netherlands have "fined tuned our strategy" to defend against Mexico and will base it on lesson learnt from its previous match with Chile, in which the Dutch team won two to nil, Van Gaal said.
"There's not such a big difference in the way that Chile plays and Mexico plays," he said. "They play according to their quality, their skills and they're very eager to win and this eagerness to win is the best part of football."
