DES MOINES — The combination of heat and scarce amounts of rain intensified the drought in several agriculturally significant states, contributing to declining crop conditions in parts of the Midwest and South.

However, the U.S. Department of Agriculture said in a separate report Thursday the expected record corn harvest and third-largest soybean crop are on track, since areas that aren’t seeing as severe a drought will produce enough to make up for the driest regions.

Crops in states such as Kentucky and Tennessee look better than they did a month ago, the USDA said, while Iowa and Missouri are suffering from the heat.

“The fringes of the corn belt are producing enough to offset Iowa’s loss,” said Chad Hart, agriculture economist at Iowa State University.

This week’s national drought monitor, which tracked conditions from Sept. 3 to Tuesday, shows nearly 50.7 percent of the contiguous United States is now in moderate drought or worse, up from just over 50 percent the week before.

The report said in Iowa, the nation’s largest corn producer, severe drought spread to nearly 42 percent of the state — up from 32 percent a week ago. All but two of the state’s counties, both in east-central Iowa, are experiencing some level of drought or abnormally dry conditions.

The trend was driven in part by unusually hot temperatures. In the Midwest, temperatures were as much as 10 degrees above normal and rainfall for many areas was sparse or nonexistent. La Crosse, Wis., for example, has received only 2.4 inches of rain between July 1 and Sept. 10 — the driest on record, said Anthony Artusa, a meteorologist with the National Oceanic and Atmospheric Administration. The city’s previous record was 2.52 inches in 1948.

The weekly drought monitor — produced by the National Drought Mitigation Center at the University of Nebraska-Lincoln, the NOAA, the USDA and about 350 drought observers — rates the level of drought on a five-classification scale: abnormally dry, moderate drought, severe drought, extreme drought and exceptional drought.

Drought worsened in portions of Illinois, Indiana, Kansas, Minnesota, Missouri and Wisconsin. Further south, conditions in Arkansas, Louisiana, Mississippi, Oklahoma and Texas declined. And more than three-quarters of the western United States remains in moderate drought or worse.

The USDA said about a third of corn and soybeans are in good or excellent condition in Iowa, down from more than half rated in those categories a month ago. In Nebraska, where drought increased in some areas, non-irrigated corn is in similar shape.

However, the USDA said corn production nationally is expected to be 13.8 billion, a record for the United States. The corn yield, or amount produced per acre, is expected to be 155.3 bushels per acre, which would be the highest average yield since 2009.

Higher corn yields for the Central Plains and across the South more than offset reductions for Iowa and North Dakota, the report said.

Farmers are expected to harvest 3.15 billion bushels of soybeans, the fourth largest on record.