Playing havoc
What’s going on with the weather?
It’s a question summer-deprived Wellingtonians couldn’t be blamed for asking: Why is Australia sweltering in a heat wave while we haven’t broken 25C all season?
The answer is a complex one, but meteorologists can offer one quick take-away: Some of that Aussie heat is now making its way across the Tasman.
The dismal summer much of the country has experienced is down to two driving factors: A huge, blocking, high-pressure ridge parked to the northwest of the country, and what’s called the Southern Annular Mode, or SAM.
The ridge has been reaching out towards Northland, keeping the region dry to the point that it’s now in drought, while other weather has had to move around it, pushing a south-westerly flow over New Zealand.
At the same time, the rest of the country had been stuck in an extensive negative phase of SAM, climate variability usually seen in spring.
Wellington, which just suffered its cloudiest January on record, hadn’t been able to break 25C all summer, according to instruments monitored at the capital’s airport.
But now that the SAM pattern was kicking into a neutral phase, our summer was beginning to escape the cooling influence.
“With this, we will actually see a shift in the pattern that we’ve had all through the summer so far,” MetService meteorologist Lisa Murray said. “And, in this particular case, it’s come across from Australia, which has had these massive temperatures where you could quite literally fry an egg on the pavement.”
Murray said that travelling heat, which was flowing across the Tasman along with smoke from huge bushfires now alight in Australia, was much of the reason Wellington was yesterday recording temperatures of 20C, even with gale-force wind and rain.
For eastern areas, such as Gisborne and Hawke’s Bay, the heat was arriving in a different form: through dry foehn winds.
“So we are actually seeing heat now . . . but we are seeing it New Zealand-style.”