July 16th 2024: High pressure

New Zealand broke a meteorological record last week when Ranfurly barometers recorded 1046.5 hPa – although provisional at this stage, that's unprecedented. In weather terms high pressure squeezes weather like clouds, storms and lows out of the way, which brings sunny weather, blue skies and light winds. This one that set the record on July 10, 2024, is a kind of persistent blocking high that forces weather away and around it.

It's responsible for the north to south airflow which, in turn, has concentrated Dunedin surfers on Blackhead Beach over the past week. It also pushes up a northeast swell for later this week.

This system – the largest high around the globe at the time – was centred directly over New Zealand. They can also occur over oceans and when they do they mess with swells. A high pressure system squeezes the ocean down and can actually take energy out of swells – that's why a lot of Indian Ocean swells that light up West Oz, don't always make it all the way to Indonesia. The high flattens them. Conversely, lows draw the ocean up like a dome and encourage swell energy in the process. That's why you often get sets building again after rain squalls roll through – especially evident in the tropics.

The worrying element right now is that we should be seeing plenty of Antarctica-born storms hugging and then peeling off the icy continent and sending polar blasts, cold air, snow and Southern Ocean swells our way. But that's not happening just yet. For the sake of the skifields I hope that will happen soon ... and we could all do with some giant Southern Ocean swells to light up the big-wave spots around our coastline.

See you at the beach ... Derek

PS We want to say a huge thank you to everyone who responded to last week's edition of Box of Light. In case you missed it you can read that edition right here. We try our best to reply to every email and message, but we were overwhelmed last week and are still responding to all the heartfelt messages. Thank you for sharing our words with loved ones and helping to support our young people. Arohanui.