UK GAS-Prompt prices fall on oversupply, higher wind output

June 6 (Reuters) - British prompt gas prices fell on Tuesday morning due to an oversupplied system and stronger wind output. * British within-day gas price down 0.35 pence to 36.15 pence per therm at 0853 GMT * Day-ahead gas price 0.30 pence lower at 36.30 p/therm. * "I assume it's all (due to) the wind and a long system," a gas trader said. * Peak wind power generation is forecast at 8.3 gigawatts (GW) on Tuesday, rising to 8.6 GW on Wednesday, National Grid (LSE: NG.L - news) data shows. * System oversupplied by 11.9 million cubic metres (mcm), with demand forecast at around 181.5 mcm and flows at 193.4 mcm/day, National Grid data shows. * Forecast demand is 25.5 mcm lower than the seasonal norm of 207 mcm/day. * Average temperatures on Tuesday could reach 17 degrees Celsius in southern Britain and are forecast to rise up to 22 degrees C over the weekend, UK Met Office data showed. * Total (LSE: 524773.L - news) flows from Norway rose by 3 mcm despite the Langeled pipeline providing 2 mcm less than on Monday. * Oil prices fell further below $50 a barrel on Tuesday on concerns that a diplomatic rift between Qatar and several Arab states including Saudi Arabia could undermine efforts by OPEC to tighten the market. * As Qatar is the world's top seller of liquefied natural gas (LNG), there are mounting concerns over any supply disruptions to neighbouring countries spilling over into global gas markets. * July gas contract was down 0.25 pence at 36.40 p/therm at 0950 GMT. * Day-ahead gas price at the Dutch TTF hub down by 0.12 euros to 14.93 euros per megawatt hour. * Benchmark Dec-17 EU carbon contract down by 0.02 euro to 5.15 euros per tonne. * Thomson Reuters (Dusseldorf: TOC.DU - news) analyst view: http://emea1.apps.cp.extranet.thomsonreuters.biz/cms/?pageid=united-kingdom-gas (Reporting by Lefteris Karagiannopoulos in Oslo; editing by Nina Chestney)