Light showers late this week in the northern Midwest and heavier rainfall in most of the region early next week will provide little benefit to drought-stricken U.S. corn and soybeans since both crops are nearing the end of their growing season, an agricultural meteorologist said on Wednesday.
"It will help some of the later crops in the north such as in Wisconsin but not much elsewhere," said Andy Karst, a meteorologist for World Weather Inc.
Karst also said there would not be enough rain to boost low river water levels, and the showers would cause no major slowdown to early harvest of the U.S. corn crop.
"Water levels will keep declining and that will be an even more serious problem for barge traffic with harvest beginning," he said.
The worst drought in over a half a century has slashed production prospects for U.S. corn and soybeans.
A Pro Farmer tour of the Midwest crop states this week showed a potential 17-year low for corn yields in Indiana. It also found soybean pod counts, an indicator of yields, down 13 percent from the three-year tour average.
The tour found Nebraska's corn yield potential below official U.S. government forecasts, but irrigated corn in Nebraska appeared to have weathered the drought well, according to the crop scouts.
The U.S. Department of Agriculture on Monday said 4 percent of the U.S. corn crop had already been harvested, the fastest start ever. The crop was planted early, then pushed to maturity by relentless heat and drought over the summer.
Dry, hot weather has parched grazing lands and turned rivers into streams, slowing or stalling barge river traffic of grains.
The U.S. Coast Guard said on Monday that 97 vessels were stranded by low water on the Mississippi River after an 11-mile stretch of the waterway was closed for dredging and to replace missing navigation buoys.
The Mississippi River is the major waterway shipping route for U.S. corn and soybeans to the key export outlet in the U.S. Gulf Port of New Orleans, Louisiana.
Karst said Tropical Storm Isaac, currently about 200 miles (320 km) east of the Caribbean island of Guadeloupe, could hit Florida and states in the U.S. Southeast by early next week, bringing rainfall and posing a threat to citrus and mature row crops.
There are differing views about the track of the storm once it nears landfall in the United States.
"The European weather model has it hitting Louisiana and Texas," Karst said.
Commodity Weather Group (CWG) on Wednesday said the storm remains a wild card and agreed the European model was tracking the storm into the U.S. Delta crop region.
Heavy rains and flooding in the Delta could harm the mature corn and soybean crops.
"The Florida track is preferred, but confidence remains low," CWG meteorologist Joel Widenor said.
"The storm could pose a risk for wind damage to Florida citrus and flooding for the Southeast corn, cotton and soybeans," he said.
(Reporting By Sam Nelson; editing by John Wallace)