June 15 (Reuters) - British prompt gas prices fell on Thursday due to an oversupplied system, stronger wind output and expectations of a new liquefied natural gas (LNG) arrival on Sunday, traders said.
* British within-day gas price down 4.45 pence to 24.25 pence per therm at 0919 GMT.
* Day-ahead gas price 3.75 pence lower at 24.25 pence/therm.
* "The system looks very comfortable and also (news about) LNG arriving on Sunday," drove the prompt gas prices lower, said a British gas trader, adding gas to power demand was low due to forecasted high wind generation.
* System oversupplied by 12.2 million cubic metres (mcm), with demand forecast at around 154.0 mcm and flows at 166.2 mcm/day, the data showed.
* Forecast demand is 49.0 mcm lower than the seasonal norm of 203 mcm/day.
* The Tessala liquefied natural gas (LNG) tanker is due to arrive at Britain's Isle of Grain terminal on June 18, Reuters shipping data showed.
* "Its still IUK maintenance and surplus gas in the absence of Rough storage injections," another trader said.
* The Interconnector UK (IUK) pipeline between Britain and Belgium is shut for annual maintenance from June 14 to June 29.
* Average temperatures on Thursday could reach 23 degrees Celsius in southern Britain and are forecast to rise up to 28 degrees C over the weekend, UK Met Office data showed.
* July gas contract was down 0.90 pence at 34.40 pence/therm.
* Day-ahead gas price at the Dutch TTF hub down by 0.17 euro to 14.93 euros per megawatt hour.
* Benchmark Dec-17 EU carbon contract up by 0.01 euro to 4.95 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 David Evans)