By Sam Nelson

CHICAGO (Reuters) - Portions of the wheat-growing areas in the Plains and the southwestern Midwest region are expected to receive crop-friendly rainfall soon, but it will come too late to help drought-stricken corn or soybeans.

The moisture will, however, benefit fall seedings of hard red winter wheat, an agricultural meteorologist said on Thursday.

"Kansas, northern Oklahoma and western Missouri could receive one to two inches or more Friday and Saturday," said Don Keeney, meteorologist for MDA EarthSat Weather. Lighter rains of a half inch or less are expected throughout the Midwest by late in the weekend, he said.

Keeney said all eyes were on the path of Tropical Storm Isaac, currently taking aim at the Dominican Republic and Haiti and gaining strength at the entrance to the Caribbean.

Isaac is set to make landfall on Monday or Tuesday in the Florida Panhandle, which could bring heavy rainfall to Georgia, South Carolina, North Carolina and the mid-Atlantic, Keeney said.

Isaac could pose a threat not only to crops, but also to the Republican National Convention, set to start Monday, August 27 in Tampa, Florida.

"For now it appears Isaac is on track to land in Florida but the European weather model shows it landing further west in Louisiana or Texas, and if that happens there could be four to six inches of rain in Alabama, northern Mississippi, western Tennessee and southern Illinois and southern Indiana as well," Keeney said.

Torrential rainfall and wind, while adding valuable soil moisture for fall wheat seeding, could harm some of the early- maturing corn and soybean crops that were already weakened by the worst drought over the summer in half a century.

The annual Pro Farmer tour of Midwest crops found signs of severe crop losses in the top two corn- and soybean-producing states of Iowa and Illinois on Wednesday. Specialists on the tour pegged corn yields at the lowest in Illinois since 1995.

A Reuters poll of 11 analysts on Wednesday estimated the 2012 U.S. corn yield per acre at 121.5 bushels, the lowest in 16 years and production at 10.5 billion bushels, an eight-year low.

In its first survey asking for estimates of the amount of corn to be harvested compared with plantings, the poll showed the percentage of harvested corn area the lowest in nine years. Continued...