HAMBURG/PARIS, Aug 28 (Reuters) - European wheat prices fell for a second consecutive session on Monday, pressured by hefty global supplies, notably in Russia.

December wheat, the most active contract on the Paris-based Euronext exchange, unofficially closed down 1.4% at 239.75 euros ($259.05) a metric ton.

Front-month September, which expires on Sept. 11, ended down 2.2% at 228.25 euros a ton.

Russia's August exports of wheat, barley and maize (corn) are estimated at a hefty 5.8 million tons, up from 5.6 million in July, the Sovecon agriculture consultancy said.

Turkey's president will visit Russia soon to discuss the collapsed United Nations deal that had allowed Black Sea exports of Ukrainian grain. News that a second vessel left Ukraine's Odesa port through a temporary Black Sea corridor without Russian attack was seen as a positive signal.

"The key for the market now is whether there will be more," a trader noted. "In the meantime, Russian wheat is making the bulk of exports," he added.

Another estimate of a smaller German crop was also overshadowed by heavy Black Sea export competition.

Germany's 2023 winter wheat crop is expected to fall 6.0% on the year, the country’s agriculture ministry estimated on Monday. Wheat suffered from late summer rain on ripe crops, which damaged quality.

“The ministry’s forecast is not a surprise and confirmed earlier estimates of a reduced harvest after rain with less German milling wheat available for export and more feed wheat,” one German trader said. “More in focus remains the huge volumes of cheap Russian wheat which is being shipped into world markets at the rate of well over 1 million tons a week in August."

Traders reported some recent EU sales of 11.5% protein wheat believed to be for shipment to Morocco and Indonesia. ($1 = 0.9255 euros) (Reporting by Michael Hogan in Hamburg and Sybille de La Hamaide in Paris Editing by Josie Kao and Matthew Lewis)