UK GAS-Prompt prices ease on rising temperatures, wind power output

* System undersupplied by 15 mcm/day

* Temperatures seen reaching 20 degrees Celsius on Tuesday

* Wind power output seen rising by 1,300 MW

April 13 (Reuters) - British prompt gas prices eased on Monday morning despite an undersupplied system as weather forecasts showed temperatures and wind power rising.

Gas for day-ahead delivery was trading down 0.45 pence at 47.75 pence per therm by 0852 GMT, while gas for within-day delivery was down 0.10 pence at 47.80 pence per therm.

Meteorologists at Thomson Reuters Point Carbon said temperatures could reach up to 20 degrees Celsius on Tuesday afternoon, compared to usual temperatures of around 12 to 14 degrees Celsius at this time of year.

Wind power output was also set to rise by an hourly average of 1,300 megawatts (MW) on Tuesday from Monday, data from Thomson Reuters Point Carbon showed, which should reduce utilities' need to buy gas.

National Grid (LSE: NG.L - news) data showed supply was forecast at 212.8 million cubic metres (mcm) on Monday while demand was seen at 228 mcm, meaning the system was 15.2 mcm undersupplied.

UK exports to Belgium rose to 30 mcm/day on Monday from 23 mcm/day on Friday, while there were also reduced imports from Norway and zero from the Netherlands via the BBL pipeline.

"Given the short system we might see higher storage withdrawals today," analysts at Point Carbon wrote.

Further along the curve, gas for delivery next month was down 0.15 pence at 45.95 pence per therm.

In the Netherlands, the day-ahead gas price at the TTF hub was down 58 cents at 22.52 euros per megawatt-hour.

The benchmark European Union carbon price was trading 9 cents down at 6.89 euros a tonne on ICE Futures Europe. (Reporting by Nerijus Adomaitis in Oslo; Editing by Nina Chestney and Dale Hudson)