A very wet end to June

It looks like northern New Zealand is in for a very wet end to June as computer models agree and agree again that a deep and large low is going to form in the Tasman Sea this weekend and take a number of days to clear the country.

The low is predicted to deepen quickly on Saturday bringing heavy rain at times to northern regions of the North Island, such as Northland, Coromandel, Bay of Plenty and East Cape, across three days starting late on Saturday/early Sunday.

Because the low is tapping in to sub-tropical air we can expect a big jump in overnight lows - hopefully this morning was the last of the black ice around Bay of Plenty. The sub-tropical air is also saturated and therefore heavy rain is very likely, especially in the ranges. Due to the size of the low it will mean prolonged periods of rain or heavy showers and this is what is likely to cause flooding in some areas, especially eastern Coromandel, Bay of Plenty, East Cape and Gisborne. I see MetService also think there's a high chance of heavy rain in Hawkes Bay.

Going back to the temperatures, some regions will really notice a massive jump in overnight lows. Waikato, for example, has had lows around -3, -5 and -7 lately. They will jump closer to 10 by Sunday night.


Speaking of frosts - you have to check out these amazing photos uploaded yesterday. This is what a hoar frost looks like, taken from around Reporoa near Rotorua - trees all white from frost. 

In Auckland, where several mornings lately have dropped to -1, overnight lows may be as much as 14 degrees warmer on Sunday night with a possible low of 13 in the forecast at this stage.

The cold, dry, weather lately has allowed the ground to firm up. I was talking to a lifestyle farmer from Kaukapakapa last night who said the weather lately has been fantastic for hardening the soil up. Unfortunately this one low may undo all of that with rain starting on Friday and coming and going right through until next Wednesday. July is usually a wet month so there's a good chance that the Auckland region may have seen its last frosts for a while.

The rain and higher temperatures wont be good news for ski fields this weekend but there is some good news for them next week - and good news for Canterbury farmers. This low may now be so far north (passing over Northland and East Cape) that it might not be able to dredge up really cold air to low lying farms. The other day it was looking like Canterbury could get a snow storm from this low but I'm not confident of that now. The good news for ski fields is that with so much moisture and a cold change coming after the northerlies, snow is likely again for most of the national ski fields - might not be heavy but it will hopefully be a good amount.

Speaking of the South Island it is probably going to be a very cold week next week...with winds mostly from the east, cloudy skies and highs only around 7 or 8. Yet again, the place to be will be in the west. Also, Alexandra will go from having highs of 2 degrees this week (yes, highs) to highs around 7 or 8. Almost tropical. High air pressure seems to be coming through in the long range computer models for the South Island next week meaning it may be quite a cold, dry, week for those in the east with gusty east or south east winds north of Canterbury.

That cold south east change will affect much of the North Island next week - Hawkes Bay and Wairarapa will be especially cold, wet, and windy.

Those winds may be gale force for in places like the Eastern Waikato, but the winds will be stronger further south like to the west of the Tararua's.

This low is very large - that doesn't make it more aggressive, it just means it's likely to affect more people for a longer period of time. I'll write a special weekend blog on Saturday or Sunday to cover off this low and where the rain is going. And be sure to check www.weatherwatch.co.nz as we'll have the highest amount of weather news updates.

Philip Duncan

Photo / Sarah Ivey