Sept 25 (Reuters) -Cotton prices edged lower on Wednesday as weakness in the oil and U.S. agricultural markets exerted downward pressure on the natural fiber, while traders assessed the impact from hurricane Helene on crops in some key growing regions.

* Cotton contracts for December CTZ4 fell 0.39 cents, or 0.5%, at 73.7 cents per lb at 12:22 a.m. EDT (1622 GMT). Prices had hit a three-month high on Tuesday.

* "We had early pressure coming in from other agro commodities, initially the Chicago grains and ICE softs which set up a negative tune for cotton," said Valentin Olah, risk management consultant at StoneX Group adding that lower crude oil prices were also putting pressure on the natural fiber.

* The U.S. dollar index .DXY rose 0.4%, making cotton more expensive for overseas buyers.

* Chicago soybean futures fell as an outlook for much-needed rains in Brazil eased worries about dry weather delaying planting in the world's biggest exporter of the oilseed while wheat and corn prices were also lower. GRA/

* Oil prices fell more than 1% as investors reassessed whether China's latest stimulus plans will be able to boost its economy and spur fuel demand in the world's largest crude importer. O/R

* Lower crude prices make polyester, an alternative for cotton, less expensive.

* Focus now shifts to the U.S. Department of Agriculture's (USDA) weekly exports sales data due on Thursday for more cues on demand for the natural fiber.

* "Seems like traders are watching the market from the sidelines ahead of the hurricane," Olah added.

* Hurricane Helene formed near Tampa, Florida, on Wednesday, the U.S. National Hurricane Center said in its latest advisory.

Reporting by Sherin Elizabeth Varghese in Bengaluru; Editing by Krishna Chandra Eluri