"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," the Holland coach said ahead of today's match.
"I'm quite conscious that it will also affect the Mexican team, but they're much more used to it than we are."
Temperatures in Fortaleza have been hovering between 25-30C in the past few weeks, considerably hotter than in Rio de Janeiro, where the Dutch team have been training, and in Sao Paulo and Porto Alegre, where they played their 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 in," midfielder Leroy Fer said. "But the other teams are also affected. We feel we are well prepared."
Fer will sit out the match against Mexico while Bruno Martins Indi is still recovering from mild concussion and will stay on the bench.
Van Gaal added: "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 condition. But he can be a substitute. He will be on the bench."
Mexico and the Netherlands continued their build-up for the match away from the Castelao arena in a bid to preserve the pitch, which "is not that good," according to Van Gaal.
The coach also revealed the Dutch have "fined tuned our strategy" to defend against Mexico and will base it on lessons learnt from their previous match with Chile, which the Dutch won 2-0.
"There's not much difference in the way that Chile play and Mexico play," he said. "They play according to their quality, their skills, and their eagerness to win is the best part of their football."