* Concern about dryness in Brazil supports soy, corn

* Weaker dollar boosts U.S. export prospects

* Heavy export competition undermines wheat

*

HAMBURG, Nov 20 (Reuters) -

Chicago soybeans and corn rose on Monday as dealers assessed forecasts of rain for parched Brazilian crops, while a weaker dollar boosted export prospects by making U.S. supplies cheaper in international markets.

Chicago Board of Trade most-active soybeans rose 0.3% to $13.44-3/4 a bushel at 1209 GMT, after dropping to its lowest since Nov. 3 earlier on Monday.

Corn rose 0.1% to $4.67-3/4 a bushe and wheat fell 0.2% to $5.74 a bushel.

Showers this week will briefly ease heat and dryness stress in north Brazil's soybean area, Commodity Weather Group said. Northern Brazil is then expected to dry out again.

Dryness is forcing some Brazilian farmers to

give up

on soybeans to plant cotton or another crop.

"The weaker dollar, positive for U.S. export prospects, is supporting grains and soybeans today along with concerns about weather in Brazil," said Matt Ammermann, StoneX commodity risk manager.

"Brazilian soybeans need more rain and more is forecast this week, but in the coming weeks the forecasts are again for hotter and dryer weather. This is also a factor supporting corn.

"The market also wants to see exactly how much of the rain forecast in Brazil actually falls. There is also the possibly that China could resume buying U.S. soybeans."

China increased U.S. soybean

purchases this month.

"Wheat is being weakened by lack of demand and strong competition in export markets to U.S. supplies, especially from Russia," Ammermann said.

Volumes in Ukraine’s

shipping channel

reaching world markets continue to develop, with the market showing lack of concern about the latest reports of incidents involving ships such as the one last week of a vessel hitting a mine.

"What was viewed as massive risk a few months ago, seems now to be considered as the normal course of business in the Black Sea," he said. (Reporting by Michael Hogan in Hamburg, additional reporting by Naveen Thukral in Singapore; Editing by Chris Reese, Varun H K and Ed Osmond)