A meteorological explanation for the heatwave

From a weather perspective, it's a pretty stock-standard scenario. From a climate perspective, it is anything but.


Crikey

It’s too darn hot – and it’s going to get hotter.

We are sweating through Australia’s second major heatwave for 2014 (and we’re just two weeks in). And it comes after the nation’s hottest year in over 100 years on records.

So why is it so bloody hot? From a weather perspective, it’s a pretty stock-standard scenario. From a climate perspective, it is anything but stock standard. The concern (and reality) is that this – longer, hotter, more frequent heatwaves – are becoming stock standard. It is no longer a prediction. We are living in a changing, warming climate.

Weather-wise, one of the main culprits of the heatwave is a 'blocking high' in the Tasman Sea that is churning hot northerly winds over south-east Australia. Normally, a high moves on after a couple of days, allowing cooler systems from the south carrying cold air to replace the heat and provide some relief. But this high isn’t moving on – not only is it deflecting cool changes, it is also the mechanism that is carrying hot air towards the south-east, day in day out.

Fortunately, it is moving away later today, so after two more days of record-breaking heat, Adelaide is forecast to get a cool change late this afternoon and Melbourne late this evening.

Blocking highs are usually a primary cause of heatwaves. But what is extraordinary about this heatwave (and more recent ones) is how hot the heat source is and the fact that there isn’t a phenomena such as El Nino 'pushing' the weather towards hotter conditions.

This record-breaking heat is occurring in 'neutral' El Nino conditions. A quick refresh: during a strong El Nino we typically see our worst droughts/heatwaves in south-east Australia, and during a strong La Nina we typically see above-average rainfall and cooler temperatures over eastern Australia. So breaking heat records for duration and intensity in these current neutral El Nino conditions is like a race car driver recording his fastest speed in rain with poor tyres.

So what’s to come?

The frequency, duration and intensity of both heatwaves and hot days have increased in the last 30-40 years, and record hot days are outweighing record cold days by three to one. Australia’s longer, hotter and more frequent heatwaves are consistent with climate change predictions – and the trend is expected to continue. Of course, there will still be cold days and cold spells – that is just the weather – but the overall climate trend is one of warming.

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