PNG have won 14 of their past 15 Tests in Port Moresby, but enter Saturday's World Cup clash as outsiders.
Samoa, led by Jarome Luai, received a heroes' welcome on Wednesday; temperatures could reach 32C at kick-off.
Assistant coach Paul Aiton called it PNG's biggest game in a generation, with the result potentially shaping the semi-final race.
Marcus Bai urged the Kumuls to make conditions count: "Honestly, good luck to them, a 2.25pm, kick-off I feel sorry for them," the former PNG international said.
Aiton said heat and humidity could help PNG: "I think it gives the boys a lot of opportunities."
PNG beat Lebanon 42-18 in their opener, then players complained drought had left the sold-out Santos Football Stadium hard.
Samoa coach Ben Gardiner said: "We plan to go out and test ourselves and if the ground's part of that test, away we go."