Today is the shortest day, but tonight won't be the coldest night

Friday, 21 June 2024

Friday is the shortest day - the winter solstice - but temperatures tonight won’t be anywhere near the coldest of the year.

Partly that’s because the lowest average temperatures always trail the solstice by several weeks. After the shortest day, the hours of daylight barely got any longer and the sunshine gets hardly any stronger for a couple of months.

It’s also because so far this winter, which started on June 1, temperatures have been above average across the country, and aren’t expected to cool off any time soon.

The airflow across the country hasn’t been coming from a cold place so far in June, Niwa meteorologist Chris Brandolino said.

“We typically need winds coming from the south or the southwest (to get cold temperatures) and that does bring in colder air.

“And quite frankly there’s been an absence of that,” Brandolino said.

“Granted we’re only about a few weeks into it, but nonetheless temperatures have been above average, and in some places well above average for the country so far this young winter season.”

Many places had colder temperatures in May than they had in June, Brandolino said.

The comparatively warm temperatures in June were a major reason for a lack of snowfall so far this year.

Temperatures weren’t expected to drop to “very cold” levels possibly for at least the next few weeks.

Typically there was a lag between the shortest day and the coldest temperatures.

“It doesn’t always work that way, but history tells us generally speaking July, maybe even early August, that’s when we find our coldest temperatures in terms of an average,” Brandolino said.

Summer was similar, with the longest day a few days before Christmas, but the warmest temperatures were usually well into January and sometimes into early February.

“There is usually about a five, six week separation between the longest day and the warmest temperatures, as well as the shortest day and the coldest temperatures.”

According to Time and Date, the daylength in Wellington on Friday is just 9 hours, 11 minutes and 22 seconds long. That’s only a second or two shorter than Thursday and Saturday.

The increase in daylength does pick up pace, but not in a hurry. June 30 is only about 2½ minutes longer than the solstice. Even the last day of July is only about 44 minutes longer.

August is a brighter story, with a daylength of 10 hours on August 3, and 11 hours on August 28.

Auckland has a daylength of 9 hours 37 minutes and 53 seconds on Friday, while for Christchurch daylength is 8 hours 56 minutes and 21 seconds.

Daylight length changes because the Earth is on a tilt as it orbits the Sun, and the solstice is technically just the instant when the South Pole is at its farthest tilt away from the Sun, which is at 8.50am Friday.