Weather Watch: Yet another change in patterns

I'm actually a little surprised how wildly different each month of winter has been this year.  June was full of southerlies that saw light snow falling to places that don't normally receive it (Napier, Wellington, Masterton) and that southerly flow meant severe frosts right across the nation, in particular Central Otago, Central Plateau, Rotorua and Waikato.  Even Auckland had several big frosts right across the city.  When July arrived the weather patterns shifted and the overnight frosts were no longer severe.  Instead the constant southerly flow was switched off while sub-tropical lows and Tasman Sea lows made an appearance.  Many weather warnings were issued during July as a number of storms swept past the nation – the most famous being the one that was supposed to hit Auckland but instead limited damage only to Northland.
 
Now we're here in August and there's yet another change in the weather patterns – this one is Spring.  We have undoubtedly shifted into a spring-weather pattern that has brought gusty, warm, westerlies to the nation for the past week.  Highs in the east have frequently touched 19 degrees and frosts are becoming limited to only one or two centres nationwide per morning.  Overnight lows are also in the late single digits for many centres even in the South Island.
 
The westerly was most noticeable this morning when at 8am it was -1 in Christchurch but a mild 11 degrees just up the road in Kaikoura. 

Today we see a breather in the weather with winds easing and skies mostly clearing… but it's all back on again tonight.  When I say a typical spring weather pattern I'm talking about the north west/south west change. This is when we see winds shifting from north westerlies to south westerlies every couple of days over a period of time.  It's caused by the wintry lows circling Antarctica and highs to the north of the country…. New Zealand then lies in between this tug of war of air pressure.  We become a nation underneath a racing track of air.
 
Like I said, tonight it's all back on again - another low pressing against the south with associated fronts heading north. That means windy in the east of both islands and around central New Zealand tomorrow and rain moving up the west coast, although the rain eases the further north it heads…I doubt it will deliver much north of Taranaki.
 
Conditions will ease as the week progresses however a new blip has appeared on the long range computer models – a potential sub-tropical low on Friday/Saturday.  With a high pressure system likely to lie to the south-east of New Zealand this could pose a threat to northern New Zealand in the form of heavy rain and severe north east gales.  Of course we'll need to wait a couple more days until the models sort themselves out… but I think a cloudy and windy forecast will be quite likely for this weekend with rain in some northern and north eastern regions.