"It would have been a very high impact situation."
A low pressure weather system to the east meant winds in the lower North Island were moving in an east to south-easterly direction, McInnes said.
"That means [Whanganui] benefits from all the ranges that act as cloud traps.
"Keeps things nice and clear and dry."
On Tuesday there's a high pressure system starting to set up, which will likely prolong the clear weather, the meteorologist added.
A front moving up the country in the middle of the week could bring a spot of rain late on Wednesday and early Thursday morning.
"Nothing too major," McInnes said.
"The one thing it will do is drop the temperature a bit."
Once it passes, things will be mostly clear, just a bit cooler towards the weekend, he added.
McInnes said ash from the massive eruption of the Hunga Tonga-Hunga Ha'apai underwater volcano in Tonga was not likely to reach New Zealand.
MetService acts as a volcanic ash advisory centre, mostly for the aviation sector, McInnes said.
As the Tongan volcano was in the tropics where winds were a lot weaker, it meant ash was unlikely to cause problems here, he said.