September marked by tumultuous weather events
Last month our community was a theatre of extreme temperature events, including one week in which the city broke both high and low September temperature records.
The entire country was hit by highs and lows that have swung in a pendulum fashion for past few months, says NIWA senior climate scientist Georgina Griffiths.
“This winter and spring has been very volatile,” she says.
On September 1 in Johnsonville a major slip in the early hours of the morning left houses in a precarious position and blocked a private driveway. The road over the Rimutaka Hills was closed by snow for several hours on 24 September, as hail pelted the city.
“Rainfall is not the story; it is more about the temperature swings.
“The Tasman Sea is full of lows and troughs and very unsettled,” Mrs Griffiths says.
Johnsonville weather enthusiast Graham Ferguson has a Lacrosse weather station installed at his home and says the data he follows most often is the strength of the wind.
“The highest speed it ever recorded was 117 km/r in 2008.
“It’s always interesting to watch and I have trouble keeping the gauge working properly, it twists and turns so much because the wind doesn’t blow in a regular direction,” says Mr Ferguson.
Local residents often inform him when the equipment fails because they follow the webcam for updates when they are out of the city, he says. Another weather reading of importance is the pressure gauge, which is useful for timing treks into the mountains.
“If you are going into the mountains it’s good to go when the North-Western is finishing and the Southerly starts,” he says.
In Wellington NIWA takes measurements from Kelburn and Upper Hutt sites, which have recorded near average temperature and rainfall figures and above normal sunshine hours. Two extreme temperature events occurred in September: a record cold on the 5th and 6th, and a record warm on the 14th.
“Then on October 5 we saw extreme, unseasonable snowfall across the North Island.
“The timing of swings between the record cold and warm is very unusual.
“What’s not normal is the swinging between the North and South winds and the lack of a westerly,” says Mrs Griffiths.
In the Pacific Ocean a “little El Nino” is currently active but having minimal effect on the country, although it is predicted to intensify over summer. If El Nino intensifies cold seas will be forced towards our shores and fewer tropical cyclones will form.
Wellingtonians take a particular interest in the weather because of its changeable and maritime nature. Locals who are adamant about the differences on either side of the Haywards, from Petone over to Johnsonville and Porirua, are generally correct, but figures normally don’t tell the full story, says Mrs Griffiths.
“Every little place has its own climate, but the deviations in numbers will be very similar,” she says.
When asked if many people call up NIWA to enquire about the weather Mrs Griffiths said, “Are you kidding, people call up all the time. That’s why we have the data online”.
NIWA predicts the coming months will see a normal temperature return to the North and be slightly cooler than normal in the South.
“What we have seen in the last six weeks is not climate change, but climate variability,” she says.
