On Northern Territory's biggest footy weekend of the year when grand finals are played in both Darwin and on Bathurst Island, heavy showers and storms are likely.

In the hours leading up to Saturday's NTFL Grand Final between the Tiwi Bombers and St Marys at Marrara there's about a 90 per cent chance of showers, some of these may be heavy. During the evening's match there is about an 80pc chance of showers and the humidity will be rising above 70pc as the temperature slides below 30.

On Sunday afternoon the Tiwi Island Grand Final is being played on Bathurst Island, 80km off the coast of Darwin. Thunderstorms are a better chance than on Saturday due to a low pressure system moving to the west of the region. "Hector" may show up during the game adding to the spectacle.

These conditions are not rare in finals but will be a stark contrast to the corresponding games in 2009. Last year's NTFL game was played on a dry ground in 60pc humidity. The Tiwi Island game was played in sunny 35-degree heat, the hottest March day on record.