UK GAS-Prompt prices rise on exports to Belgium, cooler weather

* Drop in Norwegian flows drives demand in Belgium

* Temperatures predicted to fall this week

* Two new LNG cargoes heading to South Hook

May 26 (Reuters) - British prompt gas prices firmed on Tuesday on a cooler weather outlook and exports to Belgium, after Norwegian flows to Zeebrugge fell to zero due to planned maintenance.

Gas for within-day delivery was trading 0.50 pence higher at 42.75 pence per therm by around 0815 GMT, while gas for delivery on Wednesday firmed 0.70 pence to 42.80 pence per therm.

Maximum temperatures are expected to fall from around 20 degrees on Tuesday to 15 degrees by Saturday (Shenzhen: 002291.SZ - news) , and to be below normal next week in the northwest, though near average further south and east, Britain's Met Office said.

National Grid (LSE: NG.L - news) data showed supply was forecast at 216.5 million cubic metres (mcm) on Tuesday, while demand was seen at 215.5 mcm, meaning the system was slightly oversupplied.

"Despite the currently long system, prompt prices are finding support with strong levels of export expected through the week, with flows to the Belgian hub offsetting reduced supplies," a UK gas trader said.

Exports via the UK Interconnector were expected to be around 40 mcm/day on Tuesday, up from 32 mcm/day on Friday, as demand in Belgium rose due a fall in Norwegian gas flows.

Some Norwegian gas was rerouted to Britain, resulting in higher deliveries via the Langeled pipeline after a receiving terminal in Zeebrugge was shut for maintenance on Monday.

Supply from Britain's South Hook liquefied natural gas (LNG) import terminal rose compared with Friday as new cargoes were expected to deliver gas from Qatar.

"Given the frequent cargo arrivals we expect sendout from South Hook to remain strong towards end of May and staying around 50 mcm/day," analysts at Thomson Reuters Point Carbon said.

LNG deliveries could decrease from the beginning of June as Asian demand is expected to rise, they added.

Gas for delivery in June was up 0.15 pence to 41.60 pence per therm.

A Teesside gas processing plant is expected to be shut for annual maintenance from June 2 until June 23, with flows falling by 80 percent from June 1.

In the Netherlands, the day-ahead gas price at the TTF hub was up 0.05 euros at 20.60 euros per megawatt-hour at 0820 GMT.

The benchmark European Union carbon price was trading 0.05 euros lower at 7.34 euros a tonne on ICE Futures Europe. (Reporting by Nerijus Adomaitis in Oslo; Editing by Mark Potter)