As Northland still cleans up from the devastating storm two weekends ago, MetService is warning that more rain could hit the region this weekend - and it could get heavy.

The storm that hit overnight on July 17/18 caused major flooding across Northland, inundating homes, bringing down major slips and dumping 220mm of rain - about two months worth - in a few hours.

And with the region still largely sodden, MetService has lowered its criteria for what a heavy rain warning would be for the region from 100mm in 24 hours to 70mm.

MetService communication meteorologist Lewis Ferris said this was to recognise that with the region still so damp, that amount of rain could cause more issues such as flooding and slips.

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Ferris said it was too early to say exactly how much rain would fall on the region on Sunday and Monday and Northlanders worried about it should keep an eye on weather forecasts for the next few days.

''It's too early to say get the sandbags out [to protect properties] yet, but anybody concerned about their properties really should keep up to date with what the weather is doing,'' he said.

A low over the Tasman Sea is expected to slowly move east passing north of the country during the weekend, directing a moist east to northeast flow over the upper North Island, with Northland likely to bear the brunt of any bad weather.

Current weather models are forecasting a band of rain heading Northland's way through the latter part of this weekend.

"Given the current saturated conditions [in Northland] we are wary that any persistent rainfall could have noticeable effects, so we are urging residents to remain up to date with our latest forecast information on MetService.com," meteorologist Tui McInnes said.

"Of course, even with static weather, Kiwis will know that mother nature can throw some curveballs, so it is always good to keep up to date with the latest information, and kia haumaru – stay safe."