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Dublin: 15°C Wednesday 22 September 2021

So, can we officially call this warm spell a 'heat wave'?

It’s hot. But is it a heat wave?

MEDIA OUTLETS (EVEN, we hate to admit, this one) are fond of labelling anything longer than a fleeting appearance by the sun a ‘heat wave’.

But are we correct to use the term to describe the current weather?

It’s certainly hot. But is it hot enough to call a heat wave?

Gerald Fleming, head of forecasting at Met Éireann, seemed an appropriate person to ask.

Said the forecaster:

The term ‘heat wave’ in a general sense means a prolonged period of hot weather – more scientifically we say five consecutive days in which the maximum temperature exceeds the average by five Celsius. So, five days with five degrees above the average.

It would indeed be accurate to describe the current warm spell as a heat wave, on that basis, said Fleming – as the average daytime temperature for this time of year is 18 or 19 degrees. We’ve been enjoying temperatures in the mid-20s since Saturday.

Yes, I think we can officially say a heatwave has happened or is happening.

Conditions are set to change this evening unfortunately, but not before we experience another very warm day – possibly the warmest of the week.

shutterstock_131341742 Source: Shutterstock/djgis

The weather service has issued a ‘yellow alert’ warning for the east of the country, with temperatures today set to reach 27 or 28 degrees.

The warm spell is set to come to a thundery end thereafter.

“As often happens you get the very highest temperatures just before the end,” said Fleming.

“Then you have the risk of thunder coming along – driven by those very high temperatures.

Thunder is just something that’s driven by the temperature difference between the surface temperature and the upper air. So when the surface temperature gets very high it increases the risk of thunder.

The thundery showers aren’t likely to be prolonged in most areas, said Fleming.

And while the heat wave (we’re going to enjoy bandying that term around, while we’re allowed) may not last beyond the next 24 hours, the forecast for the latter part of the week isn’t too bad.

Temperatures will still occasionally reach the high teens, in fresher conditions, tomorrow and on Friday.


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