All Norwegian citizens, with a valid Norwegian passport, can pre-vote from the 1st of July 2019. The last day of pre-voting is on the 29th August (since it takes some days to send your ballot to Norway).
For more information about the elections, see https://valg.no/en .
It is wise to call the Embassy or Honorary Consulate/Consulate Agency before you turn up to vote, to make sure of their opening hours.
The Royal Norwegian Embassy in Riyadh wish you all, as we say in Norwegian, “et godt valg!”
For more information in Norwegian, see this link.