Whanganui didn't have a heatwave last week - but it had a very warm and settled period of weather, MetService forecaster Peter Little says.

An official heatwave must have temperatures five degrees above average for the time of year for five consecutive days. Whanganui's January average is 22.1C.

The hottest temperature of late January was 26.4C on January 31. It was one of four days over 26C. But five days of 27.1C would have been needed for a heat wave.

Temperatures in Whanganui houses and cars topped that at times. But Little said temperatures have to be taken in well-ventilated and well-exposed places to meet world meteorological organisation standards.

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Cars typically take temperatures from the road in front - which can easily be two degrees hotter. And temperatures in towns are raised by the presence of buildings and concrete, and in sheltered places by the absence of air flow.

Official temperatures have to be taken out of direct sunlight, and in places with grass and no buildings.

It may not have been a heatwave, but the hot, dry weather has turned parts of the Manawatu-Whanganui into what Niwa calls a hotspot - a place with severely to extremely dry soils that can lead to a drought.

The 3.6mm of rain on February 1 did nothing to change that.

More rain is forecast with a southerly change on February 6 - but it's only likely to be a few isolated showers. The weather is expected to continue hot and dry after that.

Soils are especially dry along the coast, and a restricted fire season was declared for coastal Rangitīkei, Manawatū and Horowhenua on January 30.

Since then a permit has been needed for any outdoor fire between SH1/SH3 and the coast, the area's deputy principal rural fire officer Graeme McIntyre said.

The coast often dries out fast, and fires there endanger commercial forests.

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In February 2015 a fire on Santoft Rd near Bulls tied up many fire crews and three helicopters, and cost $100,000 to fight.

This year, on January 12, forestry slash being intentionally burned in Brandon Hall Rd flared up with an increase in wind. The blaze wasn't big but had potential to reach Santoft Forest.

It took firefighters several hours to extinguish it completely.

At the time Manawatū principal rural fire officer Bradley Shanks advised against any burning at all in coastal Rangitīkei, and predicted there would be fire restrictions soon.

Anyone who wants to have an outdoor fire in that coastal strip now needs a permit, obtained online at www.checkitsalright.nz. Any permits issued there will be suspended if a prohibited fire season is declared later.

No fires are permitted on conservation land or on the coast and its dunes at any time, McIntyre said.

In the meantime, he suggests people living in the area reduce fire risk by clearing house gutters and keeping grass and other vegetation mown or trimmed around structures and around boundaries with neighbours.

Anyone who has had an outdoor fire recently is asked to make sure it's out and cannot be reignited. And people lawn mowing or scrub cutting - which can cause sparks - are asked not to do it during the hottest part of the day.

Fire and Emergency NZ in Whanganui is also collating information and considering imposing fire restrictions, Senior Station Officer Aaron Summerhays said.