AUGUSTA, Georgia (REUTERS) - Augusta National's notoriously difficult course will be even tougher to play because of a heavy rainstorm which is expected to hit the local area on Wednesday, retired six-time US Masters champion Jack Nicklaus said on Tuesday.

While the underground SubAir system that sucks water from the course's surface should ensure speedy play on the greens, strong winds and a soggy surface will keep players off balance when the tournament begins on Thursday.

"When it's wet, it's not too bad," Nicklaus told a news conference. "Once it starts to get firm and the wind starts to blow... it blows from so many different directions that the golf course changes constantly."

Wind gusts of up to 64kmh are forecast for Thursday, according to the weather.com website.

Nicklaus, who has a record 18 career major championships, said keeping a cool head amid frustrating conditions was critical to success at the tournament.

"It's a golf course that you really need to take advantage of when you can take advantage of it. And when it's tough, you've got to be very patient," he said.

"And it is very easy to get out of being patient on this golf course," he said.

There are six shots that players really need to watch on the course - the tee shots at 2, 11 and 12, both shots at 13 and the second shot on 15, he said.

"If you're smart with those shots in the difficult conditions, and you play them pretty well, then you probably will do pretty well in the tournament," Nicklaus added.

Far from being a fault, he said the unpredictable course conditions are what makes the world famous course so special.

"What a great tournament it is, because you really never know what's going to happen," he said.