Cold air is building south of New Zealand…but when will it surge north?  WeatherWatch.co.nz graphic.

It’s hard to believe we’re almost in May as temperatures in northern New Zealand barely drop below 18 degrees at night and the South Island sees a number of centres hit 27 degrees yesterday – all thanks to a northerly flow (and Dunedin city and Masterton broke an April record). (See yesterday’s high at your place by reading Sunday’s Daily Debrief).

In fact the South Island’s east coast and inland areas yesterday were in summer weather and today looks like another warm one too with those northerlies continuing.

And while some forecasters describe the current weather in the north as ‘5 days of rain’ I’d describe it more like “5 days of cloudy, sometimes drizzly, humid” weather.  It doesn’t feel like the end of April at all and the rain (if you can call it that) reminds me of something we’d see in mid-January across Northland, Auckland and Waikato.

Bay of Plenty received something a little more substantial yesterday as the rain clouds aligned themselves properly – but it was certainly very mild.

But, don’t be fooled by the sudden warmth. The northerly flow, in part thanks to two sub-tropical lows in 7 days and a high to the east helping to feed warmer weather to us, won’t last much longer – especially if you live in southern and eastern parts of the country.

The cold air is now building south of New Zealand…we’ll start to see it arriving in short bursts. But eventually one storm will open the flood gates and the bitterly cold winter weather we may have forgotten about will surge forward and plunge us into snow, frosts, gales, hail and thunderstorms.

We have 3 days of northerlies before a cold south easterly arrives on Wednesday in the south, reaching Wellington on Thursday afternoon and the North Island’s east coast Thursday evening/Friday.

Daytime highs will be lucky to reach double digits in some places with highs only around 12 from Christchurch to Wellington by the end of the week.

Auckland and other northern centres will fair better – as the east coast absorbs the cold. Highs in western and northern places are most likely to remain around the 16 or 17 degree mark at the end of this week.

Story by head weather analyst Philip Duncan