A Hawke's Bay heat alert - what does it mean ?

The sun shines on Ahuriri in a week of high 20s-low30s temperatures in Napier. Photo / Warren Buckland

A "heat alert" for Napier and Hastings remained in place today, issued as part of a warmer temperatures warning system being trialled this summer by national weather agency MetService.

The alert was put in place for Wednesday to Friday this week, with temperatures of over 30C forecast, and with the advice: "Drink plenty of water, stay out of the sun, and avoid extreme physical exertion."

But temperatures weren't expected to be anything unusual for the area around the last week of January and first week of February, with 25C at Napier recording station Hawke's Bay Airport at 11am, and a high of 31C forecast for mid- to late afternoon.

On January 30, 2020, the temperature at the airport hit 37.4C, just 0.1C short of the highest on record for the site.

MetService says the heat alerts pilot is a first in New Zealand, developed and produced by the agency, the Climate Change Research Institute (CCRI) at Te Herenga Waka—Victoria University of Wellington, and the Institute of Environmental Science and Research (ESR).

Napier is one of 22 sites being monitored - and when a significant heat event is forecast for one of the locations – a forecast two consecutive days above a pre-set threshold for each site - a heat alert banner for the affected area will appear on the respective forecast page on metservice.com.

Currently, Gisborne has the highest threshold at 31C and Napier is at 29C, while at the other end of the scale is Hokitika at 24C, which yesterday had 50.8mm of rain with more to follow today.

MetService says the pilot is a first step towards supporting communities at greatest risk from health impacts related to climate change.

It says on its website that "strong evidence" shows that extreme heat and heatwaves have negative impacts on health.

"Extreme heat can cause illness and death, but effective planning and actions can reduce its effects on health," it says.

"Because effects of heat are associated with relative rather than absolute temperatures, even in New Zealand's temperate climate people can experience negative health effects with modest increases in seasonal temperature," it adds.

"Everyone is vulnerable to extreme heat. However, babies and infants, older people, those with pre-existing medical conditions or on certain medications are more at risk."

Meanwhile, rainfall in Hawke's Bay last month was in some areas less than a fifth of January averages, according to Hawke's Bay's monthly rain report.

It was "dry as a bone on the plains and in the main ranges," said principal scientist Dr Kathleen Kozyniak.

Figures for 40 rainfall recording sites from Te Urewera in the north to Porangahau in the south show all of the region in deficit.

It was particularly so for the area south of Te Pohue and Kaiwaka, where rainfall at 22mm of the 27 stations was under 40 per cent of the January average, and worst west of Hastings where there was just 6.5mm of rain at Ohiti and 5mm at Ngamatea, in the extremes of the region towards and into the ranges.

In central Napier the 19.5mm was 44 per cent of the January average, at Keirunga (Havelock North) the 8.5mm was 20 per cent, and Waipukurau's 8mm was 15 per cent of its average for the first month of the year.

By contrast there was 45mm of rainfall in Wairoa, 54 per cent of its January average.