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Jan 16, 2014

Hot enough for you? A meteorological explanation of the heatwave

Bit hot, huh? So what's going on with the weather patterns? Crikey asked our favourite meteorologist, Channel Ten presenter Magdalena Roze, to explain. You better get used to it.

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It’s too darn hot — and it’s going to get hotter. Get ready for the mercury to notch up a couple more degrees, with today on track to be the hottest day of the heatwave. Many towns and cities are set to break all-time records in what is now day four or five of sweltering conditions.

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 Friday, so after two more days of record-breaking heat, Adelaide is forecast to get a cool change late Friday afternoon and Melbourne late Friday 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.

*Magdalena Roze presents weather on Channel Ten news bulletins and tweets at @magdalena_roze

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32 comments

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32 thoughts on “Hot enough for you? A meteorological explanation of the heatwave

  1. Ken Lambert

    Dave C

    Why don’t we pick a nice middle of the road newspaper like the SMH of the mildly pink Fairfax stable: This is a quote from Dr Rob Massom here:

    http://www.smh.com.au/travel/travel-incidents/third-vessel-heads-to-rescue-passengers-on-akademik-shokalskiy-trapped-in-antarctic-ice-20131229-301rp.html

    “Rob Massom, an expert in sea ice at the Australian Antarctic Division and Climate Change and Ecosystems Co-operative Research Centre, said it was not unknown for sea ice to form into tight-packed ice very quickly.

    It formed from freezing of the surface of the ocean at minus 1.8 degrees, Dr Massom said.

    ”Although it’s summertime, the ice can blow around and the area can change very quickly, causing ships to get penned in the ice,” he said.

    Sea ice packs could also raft up on top of each other, doubling the thickness of the ice and forming pressure ridges several metres thick, he said. Sea ice could occur anywhere around the cost of Antarctica, but that particular area had changed due to the calving of icebergs – when icebergs break away from the land ice and float away.” endquote

    So the part played by icebergs is not to shatter into sea ice trapping Mr Turney’s boat, but to “change the area” which can only mean changing the circulation patterns of the wind and current driven sea ice.

    Make no mistake though – Dr Massom identifies clearly how sea ice forms from freezing sea water at -1.8 degC and can pack and ridge to trap a ship. No mention of Mr Turney’s shattered 3 year old land ice which came from the Mertz glacier.

    Turney’s assertion of being trapped in ice from old icebergs shattered by global warming is clearly designed to get a warmist angle on the farce playing out on the ship of fools.

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