Aug 21 (Reuters) -Spot basis bids for corn shipped by barge to the U.S. Gulf Coast continued to rise on Wednesday, while soy barge bids were steady to higher, traders said.

* Low water levels remain a concern for grain shipped on the Mississippi River and have prompted barge operators to implement draft restrictions.

* Scattered storms are expected in early September after dry weather, though more rain is needed in the lower Mississippi valley to relieve low river conditions, Commodity Weather Group said.

* Improved Chinese demand for U.S. soybeans supports soybean barge bids, brokers said, with weakness in the dollar making U.S. crops more attractive to importers.

* Exporters sold 132,000 metric tons of U.S. soybeans to China and 121,000 tons to unknown destinations for shipment in the 2024/25 marketing year, the U.S. Department of Agriculture said. It was the third consecutive day that USDA confirmed soy sales to China, the world's biggest importer of the oilseed, in its daily reporting system.

* CIF Gulf corn barges loaded in August were bid 5 cents higher at 65 cents over CBOT September CU24 futures. September corn barges were bid 4 cents higher at 76 cents over futures.

* FOB Gulf September corn export premiums were 4 cents higher at about 92 cents over CBOT September corn futures. October export premiums remained at around 81 cents over CBOT December futures CZ24.

* CIF Gulf soybean barges loaded in August were steady at about 65 cents over CBOT November SX24 soybean futures. September soybean barge bids were flat at 64 cents over futures.

* FOB soy export premiums for early September loading at the Gulf were about 110 cents over November futures, while last-half September shipments were around 90 cents over futures.

Reporting by Tom Polansek; Editing by Jamie Freed

For displays of CIF basis, click on the codes in brackets: U.S. CIF Gulf soybeans GRYM U.S. CIF Gulf corn GRYN U.S. CIF Gulf SRW wheat GRYO U.S. CIF Gulf HRW wheat GRYP
For displays of FOB basis, please click on the following codes in brackets: U.S. FOB Gulf corn GRZC U.S. FOB Gulf soybeans GRZD U.S. FOB Gulf SRW wheat GRZE U.S. FOB Gulf HRW wheat GRZF LINKS Corn prices page: cpurl://apps.cp./cms/?pageid=corn-cash-market
Wheat prices page: cpurl://apps.cp./cms/?pageid=wheat-cash-market
U.S. barge freight BG/US
U.S. export sales estimates USDA/EST
U.S. grain export summary GRA/U
Brazil soybean export prices SYBS
Brazil corn export prices SYBX
Argentina grain prices GRA/ARG
Russia grain prices GRA/RU