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Column – The weather pattern is changing…oh so slowly

Column by Head Weather Analyst Philip Duncan — Talk about two different worlds of weather right now.  On the one hand you have many people, mostly farmers, crying out for more rain.  On the other you have grape growers desperately hoping the rain stays away.  Then you have the rest of  the public, many will tell me they want rain, if not for them then for the farmers…but privately many tell me they are loving this weather.

The weather pattern has been very simple this year – a stream of highs coming in from south of Australia (which is why Aussie has still had a lot of rain – all the highs are south of them) then they cross the Tasman and spread over New Zealand.

There are rain makers everywhere.

To the north the tropics have exploded into life.  This Sunday and Monday a much weakened ex-cyclone Sandra will combine with a weak southerly low to bring rain and wind to parts of New Zealand – however my feeling is that many in the north and North Island’s east will see little in the way of saturating rains. The chance is there…but is certainly low risk in the east.

For the upper North Island – like Northland, Auckland and Waikato – the risk has increased a little in the past day, but the area of rain will be very 50/50 for the north.  The band of rain may not really get going until it’s out at sea – one to watch, but we’ve been warning people all week not to get their hopes up.  This is one time I hope I’m wrong and that this narrow area of rain perfectly fits itself over the entire upper North Island.

To the south the Southern Ocean has woken up after having the summer months off – already the storm factory is producing severe gales wrapped around big deep lows.  These are brushing the lower South Island from time to time – and as we slip further into Autumn they will head further north too.

The low this weekend will bring relief to many – but probably not the majority.

Fast forward another 10 to 12 days and long range computer models out of the US Govt show another cyclone coming towards NZ – and the models for the past couple of days have showed this one to have more energy than Sandra this weekend.  It may also impact the upper North Island.

(Image – the early rain map for March 28 shows what appears to be a tropical storm hitting the upper North Island. Confidence at this early stage is around 60% / Weathermap.co.nz)

But to be 100% open with you – we can’t put all our eggs in that basket.  We also thought Sandra would produce soaking rains for the Upper North Island when the models first hinted at it back in February…now they have backed off that just a little, placing the bulk of the energy on the South Island’s West Coast.

My gut instinct is a little nervous about being too excited by this next potential rain maker – but being cautious is a healthy thing when the nation is desperate for rain.  I know we’ve had many complaints about the flip flopping of 10 day forecasts on other weather websites.  A farmer doesnt need to see 5 days of predicted rain only to check back next time and see 5 days of sun. 

The highs are becoming less intense.

The highs aren’t lasting as long.

The highs are stretching further and further apart.  In fact the gap between the centre of the highs at the moment is about 6500kms (the Tasman is roughly 2000kms wide). In 10 days time the gap between these highs may be over 9000kms apart.  The greater the distance between highs, the greater the chances for rain makers in between.

So no immediate major relief – but im hopeful that this new trend of weakening highs and strengthening tropical and Southern Ocean lows marks the beginning of the end for the big dry…the only problem is, it may be a very slow transition if we don’t get that tropical rain maker in the final days of March.

– Philip Duncan

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