A weather advisory is now in effect for the island of Ireland as a prolonged spell of very warm and dry conditions takes hold this week. In Northern Ireland, forecasters predict temperatures will climb into the low to mid-20s, with potential to reach or exceed 25C in some areas, triggering heatwave criteria.

The Met Office has confirmed that Wednesday will begin overcast but will clear by the afternoon, delivering sunny spells and a maximum of around 24C. Conditions are expected to remain settled through Thursday and into the weekend, with the mercury rising further. Met Éireann's forecast for Ulster indicates Thursday could see highs of 26C in southeastern parts of the province, while northwestern areas may stay near 20C.

To officially constitute a heatwave in Northern Ireland, temperatures must hit 25C or above for three consecutive days. Meteorologists say current models suggest this threshold could be met. If so, it would be the region's second heatwave this summer, following a late June event that brought the hottest June day on record.

The advisory, which runs from Wednesday until Tuesday 14 July, warns of several potential impacts. Public health officials have highlighted the risk of heat stress and dehydration, particularly for the elderly, young children, and those with underlying health conditions. The public is being urged to drink plenty of water, avoid peak afternoon sun, and apply high-factor sunscreen.

Warm and humid nights are also forecast, with overnight lows not falling below 15C. There is a possibility of tropical nights, where temperatures stay above 20C, in a few places by the weekend. The UV index is expected to be high to very high, and there is also a chance of thunderstorms later in the week.

Water safety is another concern, with increased use of rivers, lakes and beaches anticipated during the spell. Officials advise swimmers and boaters to check safety guidance. Separately, the dry conditions have raised the risk of wildfires, and members of the public are asked to be vigilant when in the countryside.

Met Office Deputy Chief Forecaster Steven Keates noted that peak temperatures in Northern Ireland are more likely to be in the upper 20s, while parts of England and Wales will see hotter conditions. He said people should take the usual precautions with the heat and the sun.

This settled weather arrives as schools break for the summer holidays, and many families are expected to make the most of outdoor activities.