Aug 19 (Reuters) - British prompt prices were mixed on Monday morning, with the within-day falling due to an oversupplied system and the day-ahead higher on forecasts for weaker wind output.
* Within-day gas price fell by 1.50 pence to 25.00 p/therm by 0903 GMT.
* The within-day price fell as strong wind power output and low demand for gas created a supply surplus in Britain’s system, said a gas trader.
* The British gas system was oversupplied by 26.1 million cubic metres (mcm), with demand forecast at 132.5 mcm and supply at 158.6 mcm per day, National Grid data showed.
* Wind generation is expected to be strong on Monday, at 9.2 gigawatts (GW) out of 12.1 GW capacity, according to Elexon data. It is forecast to decline the next day to 6.5 GW.
* The September contract fell by 0.59 pence to 29.90 pence per therm.
* Day-ahead gas price rose by 0.45 pence to 26.50 pence per therm.
* The day-ahead was up in a correction to last week’s low price levels, said two traders, with one of them adding that weaker wind power output was expected on Tuesday, which could raise gas-for-power demand.
* Day-ahead gas price at the Dutch TTF hub fell by 0.03 euro to 9.57 euros per megawatt hour (MWh)
* The Dutch month-ahead gas contract, a benchmark for LNG prices as well as European gas, was down by 0.30 euro to 10.80 euros/MWh.
* The benchmark Dec-19 EU carbon contract rose by 0.36 euro to 26.32 euros per tonne (Reporting by Lefteris Karagiannopoulos in Oslo; editing by Nina Chestney)