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Winter nears with cooler, coldest days

The warmer than usual temperatures predicted in various weather outlooks have yet to arrive, with the Gisborne region having a very normal run-up to winter.

If anything, daytime temperatures are a little cooler than the 30-year average, while night temperatures are slightly warmer than the norm.

The daytime average is just a fraction over 17 degrees at the moment, compared to 17.4 for the 30-year average.

Overnight the average is just a little under eight degrees — half a degree warmer than the 30-year mean.

Sunshine hours also appear to be about usual, or slightly above usual, despite the cloudy days.

The water temperature off the beach is holding up at 17.2 degrees — ahead of the 16.9 average for the time of year.

The progress from autumn to winter has not only been heralded by the colouring and shedding of leaves, but also the two coldest days so far this year.

The 10th had a daytime high of 15.5, while the following day dropped further to a high of 14.9. Our coldest morning air temperature was 5.9 degrees on the 8th.

For the agricultural sector, Niwa's daily climate maps indicate it is “steady as she goes” with no soil moisture deficit in the district and growth conditions as good as may be expected for the time of year.

There is still a way to go to midwinter — depending, of course, on how this point is calculated.

For many people and for meteorologists, the easy division of the year into four equal seasons does the job, with winter beginning on June 1.

For astronomers used to measuring things by celestial parameters, midwinter comes at June 21, with the winter solstice.

That is when, for the Southern Hemisphere, the tilt of the Earth places the midday Sun at its lowest in the sky, resulting in shorter hours of daylight.

This does not quite coincide with the point when the Earth is furthest from the Sun, two weeks later, on July 4.

The third choice for midwinter is one for the perfectionists — the point at which it is coldest!

A study of weather records for Gisborne reveals that for the past 10 or so years July has been our coldest month, followed by August.

This is the result of the lag in the time it takes the oceans and atmosphere to respond to the slowly shifting point of maximum exposure to the Sun—- again caused by our planet's tilt and orbit around the Sun.

As water and air heat up or cool, so the seasons change.

Over the period 2010 to 2021, the average July daily temperature was just under 10.9 degrees. By August, the mean daily temperature was on the rise again, and averaged just under 11.7 degrees.

WHEN in July is it the coldest?

Using the three coldest consecutive daytime maximums as a guide indicates it is usually coldest up to the midpoint of the month.

In that period only a couple of three-day chills occurred toward the end of the month.

The coldest three consecutive July in those eleven years were in 2015, when the 8th, 9th and 10th had daily maximums that averaged a bone-chilling 7.8 degrees.