Weather watch: Biggest high on Earth great start for pip fruit season

The hot weather is good for final fruit size. Photo / APN

Temperatures have been well above average for a number of inland South Island areas lately all thanks to the most powerful high on the planet.

Hottest has been Alexandra, hitting 27C three days in a row this past week.

Stephen Darling, Pipfruit New Zealand director, said the hot weather had been good news for apples and other pip fruit.

"Warm weather will give us a great head start for final fruit size."

He said growers still needed to be prepared for wintry cold snaps, as we saw on Friday.

We have another big high moving in for next week too - and the North Island and eastern areas of both islands should reap the benefits with settled, warm weather.

The extra hot air over Central Otago this past week was all thanks to gentle winds from the north being heated as it passed over the mountains due to that powerful high.

Most highs in New Zealand are around 1020 or 1030hectopascals (hPa) - but, at its peak, this one measured a whopping 1047hPa. An analogy would be like saying Auckland normally gets to 18C in November but today it hit 30C.

People often ask me about hectopascals. It's a simple measurement of the air pressure - the weight of the air above. The higher the reading the more compacted the air is - in short this means the high clouds dissolve and weather is settled and stable.

The lower the pressure goes the more likely air is thinner aloft and rising air makes clouds, rain and wind.

Average pressure is about 1012 - so a high is regarded as anything above 1012hPa. Anything under 1010hPa can bring heavier rain and stronger winds.

Winds are created when the pressure difference is great over a short distance - for example 1000hPa in Wellington but 1020hPa in Auckland.

Every time a large high forms that makes more isobars on the weather map, often creating strong winds around the periphery.

Most of our rain storms sit around the 980 or 990hPa range. Bigger storms, like the huge Southern Ocean one in September, can drop down to 940 or lower.

My thanks to Bob McDavitt for also contributing to this column.