CHICAGO (Dow Jones)--U.S. soybean futures are expected to start at a 28-month high Tuesday as forecasts show little chance for rain in hot, dry areas of Argentina and raise concerns about dryness developing in southern Brazil.

Traders predict soybean futures will start 7 to 9 cents a bushel higher at the Chicago Board of Trade. In overnight electronic trading, soybeans for January delivery, the nearby contract, ended up 8 cents, or 0.6%, at $13.81 a bushel after reaching $13.85 1/4, the highest price for a front-month contract since August 2008. Soybeans for March delivery, the most active contract, advanced 7 3/4 cents, or 0.6%, overnight to $13.92 1/4.

Futures prices rose as forecasts called for hot, dry weather to stress crops in Argentina for at least another week. Unfavorable weather recently has sparked concerns about tight world supplies of soybeans, as Argentina is the world's third-largest soybean exporter and the leading exporter of soy products.

Export business may shift to the U.S, the world's top soybean exporter, if crops in South America fall short. Demand for U.S. soybeans already has been red-hot, with China, the world's largest soybean importer, snapping up the oilseed at a record pace.

"Concern continues to build regarding the weather for the corn and soybean crops in Argentina as more days with heat and dryness are recorded," private forecaster Freese-Notis Weather said Tuesday.

Traders are keeping an eye on conditions in southern Brazil, as drier weather during the next week is expected to deplete soil moisture, according to Telvent DTN, a private weather firm. Brazil is the world's second-largest exporter of soybeans.

Soybeans will be harvested in Argentina and Brazil this spring. Planting is mostly finished, with about three-quarters of the crop sown in Argentina.

-By Tom Polansek, Dow Jones Newswires; 312-341-5780; tom.polansek@dowjones.com