GRAINS-Ample supply pressures wheat; weather weighs on corn, soybeans

(Recasts with U.S. trading, adds new analyst quote, changes byline, dateline; pvs PARIS/SINGAPORE)

CHICAGO, Aug 16 (Reuters) - Chicago Board of Trade wheat futures sank to contract lows on Wednesday as ample global supplies provided overseas buyers with cheaper alternatives to U.S. offerings in export deals, traders said.

Corn and soybean futures also were lower, pressured by good weather for crop development across the U.S. Midwest. Both corn and soybeans hit their lowest levels since late June.

"Rains moving across the western Corn Belt this morning should bring heavy rains west of the Mississippi, with the eastern Midwest also picking up a half inch to an inch according to maps for the next week," Farm Futures analyst Bryce Knorr said in a note to clients.

At 10:03 a.m. CDT (1500 GMT), CBOT December corn futures were down 3 cents at $3.65-1/2 a bushel. CBOT November soybeans were 1 cent lower at $9.23-1/4 a bushel.

CBOT September soft red winter wheat was 8 cents lower at $4.21-1/2 a bushel.

Egypt, the world's top buyer of wheat, said on Wednesday that Russian suppliers made the lowest offer in its latest tender for the grain. There was no U.S. wheat offered in the tender.

"Wheat prices in Chicago slumped from the start of the week due to the rise of supplies in the world, mainly caused by bumper harvests in the Black Sea (region)," consultancy Agritel said in a note.

While large volumes purchased in the tenders could be supportive for prices, a wide gap between Black Sea origins such as Russian wheat and U.S. and west European origins may maintain price pressure.

But strong export demand was limiting the declines in soybeans.

A delegation of importers from China signed agreements to buy 3.8 million tonnes of U.S. soybeans valued at about $1.56 billion at a ceremony in Omaha, Nebraska, on Tuesday, the U.S. Soybean Export Council said on Wednesday. (Additional reporting by Naveen Thukral in Singapore and Gus Trompiz in Paris; Editing by David Evans and Tom Brown)