KANSAS CITY, Mo. — The drought that has settled over more than half of the continental United States this summer is the most widespread in more than half a century. And it is likely to grow worse.

The latest outlook released by the National Weather Service on Thursday forecasts increasingly dry conditions over much of the nation’s breadbasket, a development that could lead to higher food prices and shipping costs as well as reduced revenues in areas that count on summer tourism. About the only relief in sight was tropical activity in the Gulf of Mexico and the Southeast that could bring rain to parts of the South.

The unsettling prospects come at a time of growing uncertainty for the country’s economy. With evidence mounting of a slowdown in the economic recovery, this new blow from the weather is particularly ill-timed.

Already some farmers are watching their cash crops burn to the point of no return. Others have been cutting their corn early to use for feed, a much less profitable venture.