U.S. soybeans fell on Monday, retreating more than 2 percent from a new peak set in early trade as they tracked crude oil lower on revised forecasts that Tropical Storm Isaac would not become a Category 2 hurricane as feared earlier.

New-crop November soybeans' decline from a contract high of $17.60-1/2 per bushel weighed on corn and wheat futures at the Chicago Board of Trade as U.S. crude oil futures gave up early gains to tumble $1.25 per barrel to $94.91 at 11:09 CDT. ( 1609 GMT ) .

Isaac was barreling across the Gulf of Mexico after skimming past south Florida, and based on its current track was due to slam into the Gulf Coast between Florida and Louisiana by Tuesday night or early Wednesday -- the seventh anniversary of Hurricane Katrina, which devastated New Orleans.

Barge traffic between Baton Rouge, Louisiana, and the U.S. Gulf has been suspended due to Isaac, the Crescent River Port Pilots Association said on Monday morning.

The Mississippi River is a major channel for the movement of grains produced in the Midwest farm belt to export terminals at the Gulf of Mexico for shipment across the world.

Grain movement is set to pick up in the coming weeks as farmers in the Midwest -- where 75 percent of the country's corn and soy crops are grown -- begin harvesting in earnest.

Cash market prices for soybeans in the Midwest have begun to fall in anticipation of the harvest, which was also seen weighing on futures which have rallied to a record high after the worst drought in 56 years devastated crops.

"Soybeans are tracking oil lower after the downgrade of Isaac from a Category 2 to Category 1," said grains broker Dan Anderson of ABN Amro in Chicago.

Isaac is forecast by the U.S. National Hurricane Center to not strengthen beyond Category 1, the weakest type of the five-step Saffir-Simpson scale of hurricane intensity. There were fears it would be a Category 2 storm.

New-crop November soybeans were down 0.8 percent at $17.18 at 10:59 Central (1559 GMT) .

December corn was down 0.3 percent at $8.06 while December wheat was down 0.6 percent at $8.83-1/2.