LONDON, Aug 2 (Reuters) - Prompt British wholesale gasprices rose on Thursday as domestic production ramped down inanticipation of a planned outage at the Forties pipeline onFriday, leaving the system slightly undersupplied.
* Day-ahead gas up 0.50 pence at 58.25 p/thermat 0830GMT
* Within-day contract up 0.73 pence at 58.53p/therm
* British offshore gas production is seen at 68 millioncubicmetres (mcm) on Thursday but is expected to drop to 46 mcm onFriday, when the Forties oil and gas pipeline system is due toshut down for maintenance.
* Additionally, Shell said a planned outage at its SEALpipelinesystem from the Elgin and Franklin fields had been moved forwardto start on Thursday rather than Friday.
* Maintenance at the SEAL pipeline system is due to end onAug. 7
* According to National Grid data, demand is expected at156.2 mcmand flows at 154.0 mcm
* Exports to continental Europe through the InterconnectorUKareseen lower at 34 mcm and there may be withdrawals from storageon Friday in reaction to the Forties shutdown, Thomson Reutersanalysts said in a daily note.
* Wind generation is expected to halve on Friday, whichcouldraise gas-for-power demand
* Wind generation is expected to peak at 5.4 gigawatts (GW)onThursday and drop to 2.0 GW on Friday, according to Exelon data.
* The Boris Vilkitsky liquefied natural gas tanker isexpected toarrive at Isle of Grain on Friday but there is enough storagespace at the import terminal for sendout to remain flat.
* Further along the curve, the September contractfell 0.2 pence to 57.60 p/therm
* Winter 2018 contract edged higher by 0.25pence to63.45 p/therm
* Day-ahead gas price at the Dutch TTF hub down0.15euro at 21.98 euros per megawatt-hour
* Benchmark Dec-18 EU carbon contract slipped by0.13euro to 17.65 euros per tonne(Reporting by Sabina Zawadzki; editing by Nina Chestney)
