What is a heatwave and how is it declared?

An average temperature of 30°C by day and 15°C overnight for at least two consecutive days would trigger a heat-health watch alert (this figure varies slightly around the UK). These temperatures can have a significant effect on people's health if they last for at least two days and the night in between.

The Met Office has a warning system that issues alerts if a heatwave is likely.   See here for more information.


Level one is the minimum alert and is in place from 1 June until 15 September (which is the period that heatwave alerts are likely to be raised):

  • the minimum alert simply means that people should be aware of what to do if the alert level is raised
  • if a level two alert is issued, there is a high chance that a heatwave will occur within the next few days
  • the level three alert is when a heatwave is happening
  • the level four alert is when a heatwave is severe 


Advice during a heatwave

  • stay out of the heat
  • keep out of the sun between 11am and 3pm
  • if you have to go out in the heat, wear UV sunglasses, preferably wraparound, to reduce UV exposure to the eyes, walk in the shade, apply sunscreen of at least SPF15 with UVA protection, wear a hat. Wear light, loose-fitting cotton clothes. This should minimise the risk of sunburn
  • avoid extreme physical exertion
  • have plenty of cold drinks, and avoid excess alcohol, caffeine or drinks high in sugar. If drinking fruit juice, dilute it with water. Eat cold foods, particularly salads and fruit with a high water content and when travelling ensure you take water with you
  • look out for others: Keep an eye on isolated, older people, ill or very young people and make sure they are able to keep cool. Ensure that babies, children or older people are not left alone in stationary cars. Check on older people or sick neighbours, family or friends every day during a heatwave. Be alert and call a doctor or social services if someone is unwell or further help is needed
  • keep your environment cool: Keeping your living space cool is especially important for infants, older people or those with long-term health conditions or who can’t look after themselves
  • shade or cover windows exposed to direct sunlight and keep windows that are exposed to the sun closed during the day external shutters or shades are very effective, while internal blinds or curtains are less effective but cheaper and easier to install However, care should be taken with metal blinds and dark curtains, as these can absorb heat – consider placing reflective material between them and the window space
  • open windows at night if it feels cooler outside, although be aware of security issues especially in ground floor rooms. Close curtains that receive morning or afternoon sun.
  • turn off non-essential lights and electrical equipment – they generate heat
  • keep indoor plants and bowls of water in the house as evaporation helps cool the air
  • electric fans may provide some relief, if temperatures are below 35°C
  • seek medical advice if you are suffering from a long-term medical condition or taking multiple medications
  • if you or others feel unwell seek medical advice
  • if you feel dizzy, weak, anxious or have intense thirst and headache, move to a cool place as soon as possible. Drink some water or diluted fruit juice to rehydrate, avoid alcohol and caffeinated drinks like tea or coffee
  • if you have painful muscular spasms (particularly in the legs, arms or abdomen, for example after sustained exercise during very hot weather), rest immediately in a cool place and drink electrolyte drinks. We say that most people should start to recover within 30 mins and if not, they should seek medical help. Consult your doctor if you feel unusual symptoms or if symptoms persist


Download Advice 

NHS England have produced advice guides to help during a heatwave.  The guides are available in a number of formats and are available to download here