Temperature drop begins in Southland

It's been incredibly warm this week - on Monday 31 towns and cities across New Zealand climbed over the 20 degree mark with half of those places between 24 and 27 degrees, then again yesterday another 30 centres reached over 20 degrees.

Overnight lows across the North Island, particularly the upper half, have been in the late teens as high as 19 degrees with humidity in the 90 per cent range...this makes for a 'feels like' temperature in the mid 20s...at night, in late April, just 4 and half weeks out from the official start of winter. Some love it, others miss the cooler evenings. Which do you prefer? Personally I like the little extension to summer.

During a radio interview on Monday I came up with a (possibly ridiculous) analogy - I said the current warmth is a bit like drinking too much alcohol. It feels good at the time but you know you're being influenced by something and that there will be a catch. In this case the catch, or hangover, will be a sharp drop in temperatures starting in Southland and spreading northwards over the next 72 hours reaching Auckland late on Friday.

The winds will be southerlies or south'easterlies as they spread north - that means Southland, coastal Otago, Canterbury, Wellington, coastal Wairarapa and Hawkes Bay will be the most exposed regions and will absorb most of the coldest air. Day time highs, this week in the mid to late 20s in many of these regions, will seriously struggle to climb over 10 degrees. Thursday, Friday and Saturday look cloudy, showery and cold with highs between 9 and 12 degrees for many of these places.

Aucklanders and those in the north won't see such a dramatic change in conditions but a change is coming. Today will see a number of fronts passing through and the air temperature will drop just a little by Thursday. On Friday that southerly change will come through and by the weekend highs in Auckland will be at a more 'normal' level with 16 or 17 the highs and overnight lows in the lower double digits. Humidity levels will also fall.

Like I said earlier in the week this low is huge in size and the bigger a pressure system is the longer it affects us. In this case it's really bringing 5 to 7 days of unsettled weather to the country - warm at the start, cold at the end. The typical low pressure set up. It's brought some massive rain totals - 500mm or half a metre to Mt Cook, thousands of thunderstorms off the West Coast, flash flooding to Greymouth, surface flooding to Wellington and of course the summer highs (and lows) right across New Zealand. Is this a sign of what we'll be seeing this winter? It may well be.

Of course this Saturday marks the beginning of duck shooting season - the low will be easing by then and may well bring ideal duck shooting conditions to many. I'll provide a special forecast in my Friday Herald blog.

Finally, the weather around Auckland has been incredibly difficult to forecast over this past week. This low is especially slow moving and Auckland is on the outer fringes of it which makes things even harder to work out. You may have noticed some forecasts over the past 7 days haven't matched what has actually happened - so just a reminder that we (The Weather Watch Centre) now have our own independent weather forecasts for Auckland, they're also completely independent of MetService. We have no fancy graphics, no big weather maps - just forecasts written in a really easy to read way, and I like to think they're pretty accurate too. We're running this as part of a trial in Auckland on a couple of our radio stations and have now placed them online for the general public - so please check it out alongside your usual source of weather forecasts (such as the Herald) and compare the two... we're keen to hear your feedback, positive or...well, constructive!

Philip Duncan

Photo / Wairarapa Times-Age