Niwa forecasters find the start of summer by calculating the hottest 90 days in each 12-month period

Forecasters in Niwa tried to determine the onset of summer by reviewing temperature records and calculating the hottest 90-day periods every 12 months.

By this definition, the earliest onset of summer was on November 22, 2017, while the last onset was on January 5, 1976. On average, summer began on December 14.

“While the start of summer dates jump when looking at the hottest 90-day period each year, no clear pattern emerges that summer becomes earlier or later,” the forecaster said. by Niwa, Nava Fedaeff.

“The summer period is getting hotter, however – an expected result, given global warming.”

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The start date calculated by Niwa’s calculations is different from the start date of the meteorological summer, which is December 1.

When does summer start?  It depends.

Provided / Content

When does summer start? It depends.

It’s also different from the astronomical summer, which begins on Wednesday. It is the longest day in the southern hemisphere, when the Sun reaches its highest position in the sky.

With the astronomical definition, the equinoxes and the solstices mark the beginning and the end of the seasons.

Depending on the time and date, the summer solstice is Wednesday at 4:59 a.m.

Technically, this is the time of year when the southern hemisphere is most tilted towards the Sun. The Sun is also directly above the Tropic of Capricorn, located about 23.5 degrees south of the equator.

Time for those outdoor gatherings.


Time for those outdoor gatherings.

The time and date put the sunrise in Auckland at 5:58 a.m. on Wednesday and sunset at 8:40 p.m., resulting in a day length of 14 hours 41 minutes and 37 seconds. That’s less than a second longer than Tuesday and 3 seconds longer than Thursday.

According to the meteorological definition, the seasons are divided into groups of three calendar months.

“Calendar months align closely with temperature models, which made it much easier for us to calculate statistics and analyze trends,” said Fedaeff.

Another way to calculate the onset of summer is the thermal seasons approach used by some Scandinavian countries. In this system, summer begins when temperatures exceed a certain threshold for several consecutive days.

It was like the start of summer in New Plymouth at the end of November.


It was like the start of summer in New Plymouth at the end of November.

Niwa said that this method gives a dynamic response to the natural world and can be used in a practical way, such as in the agricultural industry when irrigating crops.

“If we defined seasons like this here, we would see an earlier start and a later end to summer, with our shoulder months warming due to climate change,” Fedaeff said.

This summer had started very warmly.

“December is currently on track to make our top 10 hottest on record, but it has also been very humid in places and some might argue that it is not summer at all,” said Fedaeff.

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