UK GAS-Prompt prices edge higher on slight undersupply

LONDON, March 30 (Reuters) - Prompt British wholesale gas prices edged higher on Thursday morning in a slightly undersupplied system but are likely to come under pressure later in the day, traders said. * British day-ahead gas price up by 0.10 pence to 39.60 pence per therm at 0807 GMT. * Within-day contract up by 0.35 pence to 39.85 p/therm. * System undersupplied by 3 million cubic meters (mcm), with demand forecast at 219.7 mcm and flows at 216.7 mcm/day, National Grid (LSE: NG.L - news) data shows. * Traders said other market fundamentals are bearish and that this could lead prices to drop later in the day, despite the slight oversupply * "The system is short today but wind is strong which has restricted gas demand for power burn. We expect storage and/or LNG (liquefied natural gas) to cover the shortfall," said Wayne Bryan, analyst at consultancy Alfa Energy. * Shell (LSE: RDSB.L - news) said an offshore outage, cutting output at Britain's Bacton Seal gas terminal, had ended and that flows were ramping up throughout the day. * Britain's Met Offices forecast temperatures could reach as high as 21-22 degrees Celsius in the southeast of the country. * Peak wind power output forecast at 6 gigawatts (GW) for Thursday, edging up to 6.1 GW on Friday, National Grid data showed. * Four LNG tankers are due to arrive in Britain over the next two weeks, adding to supplies. * April gas contract (TRGBNBPMJ7 ) down 0.30 pence to 40.00 p/therm. * Summer 2017 contract down by 0.25 pence to 39.85 p/therm. * Day-ahead gas price at the Dutch TTF hub up by 0.23 euro to 15.23 euros per megawatt hour. * Benchmark Dec-17 EU carbon contract down by 0.05 euro to 4.71 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 Susanna Twidale; editing by Nina Chestney)