MetService meteorologist April Clark said Tuesday would be Whanganui's wettest day this week, but long, fine periods would be few and far between in the next few days.
"A cold front moved over the region on Tuesday, and it's becoming stationary over the North Island Wednesday," Clark said.
"There'll be scattered light rain, about 1.5mm an hour, but it should ease slowly throughout the day.
"That front doesn't actually move anywhere, it just slowly weakens because we have a ridge of high pressure moving over the country.
"Thursday will see a few fine spells, but with afternoon and evening showers, which will be inland and away from the city. There'll be light winds and some sea breezes around the coast."
Cloudy periods were forecast for Friday, Clark said, with isolated showers that would clear in the evening.
"The high in Whanganui city will be 17C Wednesday and then 20C on Thursday.
"That'll move up to 23C on Friday, so it's warming up a little bit. Solar radiation is starting to amp up, and having more sun makes a difference during the day now."
Clark said a new front would begin to move in from the southwest on Saturday, with cloud increasing and rain developing.
"Not the best if you're heading out trick or treating I'm afraid.
"Sunday will bring more showers, but they'll slowly become isolated as we head into the later parts of the day.
"This is pretty typical for spring. You get a front, then a bit of a ridge, then another front coming on again."