Heat alert trial - Summer 2023

Heat alert trial aims to help reduce health impacts from hot weather

Extreme heat during summer can be draining and have an impact on people’s daily lives – especially their health and wellbeing. 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. International research shows that extreme heat and heatwaves can cause illness and death, but effective planning and actions can readily reduce its effects on health.

MetService will issue a heat alert for 46 towns or cities, if the forecast temperatures are expected to be unusual (very hot) for that location. This alerting scheme is not designed to capture every hot summer day, but rather focus on ‘top end’ heat. Of course, the thresholds to trigger a heat alert vary a lot from one region to another – what is considered extremely hot for a Cantabrian is very different to what a Southlander will deem hot.

The alerting will run from 1 November 2023 through to 31 March 2024 and when an alert is triggered a heat alert banner will appear on the respective forecast page on metservice.com and on the MetService weather app. In addition, forecasters will add in heat wording as part of the written forecast for each location. MetService may also use social media to generate awareness of the heat event.

This is the third year that MetService has been trialling heat alerts to help New Zealanders plan and prepare for extreme heat, alongside our Civil Defence and Health partners.

This year, the influence of El Niño conditions across the Pacific is forecast to bring a hotter than usual summer across the eastern areas of Aotearoa New Zealand, leading to additional concern in these regions.

Tips for managing in hot weather events

If you or others feel unwell

If you feel dizzy, weak or have an intense thirst or headache you may be dehydrated.

Drink water and rest in a cool place. Seek help if symptoms persist.

If you are experiencing painful muscle cramps, your body may need electrolytes as well as fluid.

Drinking oral rehydration solutions or zero sugar sports drinks may help.
Seek medical advice if heat cramps last for more than one hour.

Keep medicines below 25 degrees C or in the refrigerator (read the storage instructions on the packaging).

Keeping yourself and others safe in hot weather:
Drink plenty of water - try to drink two litres per day	Stay out of the sun
Have plenty of cold drinks	If you need to be in the heat, stay in the shade where possible
Avoid drinking alcohol, caffeine, and hot drinks	Use sunscreen
Eat nourishing food with a high water content (such as salads and fruit)	Wear a hat
Dress yourself and children in light clothing, cool cottons and natural fabrics are best	Avoid extreme physical exertion
People and pets should not be left in stationary vehicles	Take a cool shower of bath
Check in on others, especially those at most risk, children, elderly or those with health issues	Spray or sprinkle water over skin or clothing, a damp cloth on the back of the neck can help

Tips for keeping your home cool
Open windows in the evening and overnight, once temperatures have cooled	Turn off non-essential lights and electrical equipment – they generate heat.
Home insulation will help keep your home cooler in summer	Move into a cooler room if possible, especially for sleeping
Keep light-coloured curtains or blinds closed on windows facing the sun during the day. Dark coloured curtains or blinds are best left open as they absorb the heat	Use electric fans to keep cool
Use the cool cycle on a heat pump. Clean heat pumps – vacuum the filters regularly.

For more information about managing heat, head to https://www.civildefence.govt.nz/cdem-sector/consistent-messages/other-hazards/

What happens when a threshold is met?

When a significant heat event is forecast for a location, a heat alert banner will appear on the respective forecast page on metservice.com and on the MetService weather app. In addition, forecasters will add in heat wording as part of the written forecast for each location. MetService may also use social media to generate awareness of the heat event.

When will the heat alerting be in force?

From 1 November 2023 through to 31 March 2024.

History of the heat alerting scheme:

Heat alerting was originally developed and produced by MetService for summer 2021, in partnership with University of Waikato and the Institute of Environmental Science and Research, to warn people in New Zealand of unusually hot weather. This was the first time than operational heat alerting was employed here in New Zealand, covering 22 town and city locations, and using ‘feels like’ apparent temperature to capture hot, humid weather that is typically less well tolerated than hot, dry weather.

The heat alerting scheme was expanded for summer 2022, with MetService monitoring heat for 44 urban areas across Aotearoa. In the second trial, a heat alert was triggered by either a day with an extremely high (record or near record) temperature, regardless of humidity, or when a run of very hot and humid weather was forecast.

With extreme heat events worsening in response to human-induced climate change, a national heat warning system will be important to New Zealanders in the not-too-distant future. The trials undertaken over the last two years have served as a useful learning opportunity towards that goal.

What’s new this year 2023:

In partnership with NEMA, Civil Defence, and our health partners around the country, MetService will initiate a third year of heat alerting to help New Zealanders plan and prepare for extreme heat this summer.

MetService meteorologists will monitor heat for 46 sites across New Zealand this summer.

Based on public feedback and forecast verifications from the last two years, some changes have been made to the heat alerting scheme for summer 2023. The most obvious change is that MetService has simplified the wording used in a heat alert to ‘very hot’ or ‘extremely hot’.

Similarly to last year, a heat alert will be triggered if a single day is forecast to hit an extremely high (record or near record) temperature, regardless of humidity. The maximum temperature trigger thresholds are once again site specific and have not changed – they are set high, to trigger on average, about once a year.

Heat alerts will also trigger when a run of very hot and humid weather is forecast. Once again, trigger thresholds are site specific and are set high (in an average summer, thresholds would be met about once a year).