Updated

"I drove in and I could hardly get into the car park because it was so wet. The wheels were spinning and the car was going sideways trying to get parked."

That was Rory McIlroy describing the parking lot conditions on Tuesday at Merion Golf Club in Ardmore, Pa., the site of this week's 113th U.S. Open.

Yes, the Philadelphia-area course is getting doused. A month's worth of rain (over 3 1/2 inches) fell on Friday and another inch came down Monday. At 80 degrees and sunny, conditions were near perfect on Wednesday afternoon, but it isn't expected to last, as Thursday's forecast calls for a 60 percent chance of showers and thunderstorms.

The incessant precipitation has many predicting a birdie fest.

The USGA gambled when it chose Merion for the 2013 Open. At just under 7,000 yards, the historic club's East Course is noticeably short by today's championship standards, with most courses playing around 7,600 yards.

To counter the lack of distance, the USGA planned for its usual Open set-up of firm and fast, where off-line tee shots and poor approaches would be punished. But Mother Nature had a different idea. Buckets and buckets of rain have rendered the ground soft and slow, conditions which embolden players to go for the flags (or, in this case, wicker baskets).

The last thing the USGA wants is a scenario akin to 2011, when McIlroy abused soggy Congressional and finished at 16-under-par, which set records for lowest score and lowest score in relation to par in U.S. Open history.

But the world No. 2 player doesn't see cause for concern.

"I expect the scores to be a little lower than what they would be if the course was a little firmer and drier, but I don't think you'll see scores like the (ones) that were shot at Congressional a couple years ago," McIlroy said.

There are several reasons why Merion will prove a tough test, regardless of the conditions.

THE ROUGH

"You've got to hit it in the fairway," McIlroy said. "It's a pretty tight golf course. And when you do get it in the rough, you're not going to make birdies out of there."

The USGA made the course even tighter by eliminating the first cut of rough on both sides of the fairway at each hole. The rough is thick and punishing and if players find it off the tee, they will be advancing the ball back into the fairway instead of going for the green.

MUD BALLS

If the forecast holds and the rain comes Thursday, mud balls will follow. Clear skies and moderate temperatures are expected from Friday on, but as the sun bakes the fairways, shots will bite on the drying grass and the soft ground underneath will cling to the ball.

The USGA does not support the lift, clean and place method, so players will be forced to play the muddy orbs as they lie.

"When you have a mud ball, there is no predicting what happens," said 2010 Open winner Graeme McDowell. "If it's a long shot, it literally can cost you multiple shots.

"I think mud balls are a problem. I think they are unfair."

Fair or not, mud balls may be inevitable. And scores will almost certainly suffer as a result.

THE LAST 5

Birdies can be had at Merion, but from holes 14-18, they will be earned.

The short, 115-yard par-3 13th gives way to what is considered one of the toughest closing stretches in all of golf. Three tricky par-4s precede the 246- yard par-3 17th, where running the ball up is not an option. A 521-yard par-4 - the site of Ben Hogan's famous 1-iron shot at the 1950 U.S. Open - closes the gauntlet.

"I missed my drive slightly off the back tee last Wednesday, I missed the fairway. They've got all the length there," McDowell said of the 18th.

"You've got to hang on for dear life those last five holes," he continued. "I can't think of a tougher finish that I've seen at a U.S. Open."

McIlroy confirmed: "I don't think too many guys are gonna pick up shots over that final stretch."

FATIGUE

Soggy conditions may make for easier approaches, but they can take a physical toll.

"The ground is going to be heavy," said the 24-year-old McIlroy, one of the more physically fit players in the game. "It's going to be a tough walk out there."

His plan? "Conserve as much energy as you can between rounds," he said.

"It just wears on your legs," said Sergio Garcia.

MOTHER NATURE IS FICKLE

What do weather men really know, anyway? Earlier in the week, most forecasts called for a 90 percent chance of rain on Thursday. Now, that number is down to 60.

The point is weather patterns and forecasts change. An assistant pro at Merion said that if the rain holds off Thursday, the course will be firm and fast by Friday, rendering the entire issue moot.

Yes, the near-Biblical amount of rain dumped on Merion in recent days may lead to lower scores, but this certainly isn't a doomsday scenario. Players will be forced to adjust to the unpredictable conditions, and whether it's firm and fast or soft and slow, the unique layout will prove an adequate Open test.