Sub-tropic storm on its way

A sub-tropical storm is moving our way this weekend and it has the potential to have a big impact. The low will rapidly deepen over the next 24 hours and the centre is lined up to move very near northern New Zealand

This storm has the potential to be damaging both in terms of wind and rain. High air pressure to the south and this deep low to the north, coupled with its position (north west of Northland) means the winds will be strong to gale even severe gale over northern parts of the North Island, extending as far south as Central Plateau and possible even further south. Heavy rain will also be fed in to northern parts of the North Island and I'm pretty sure MetService will issue more wind and rain warnings. They have just issued warnings for Northland, Auckland, Waikato, Coromandel, Bay of Plenty and the eastern Waikato.

Monday was the first time the low came up on the computer models but in the past day or so the computer models have firmed up their predictions and they all point to this intense low brushing to the east of Northland and East Cape starting on Saturday in the north and lasting until Monday in the east.

When a system "brushes" us it means that forecasts can change quite dramatically. If the low shifts, even just a little, it could have a significant impact on the land forecasts. For example, if it drifts further to the east then the heavy rain and winds may not be as intense. A slight shift to the west could see a big increase in rainfall numbers and in the severity of the winds. The air pressure looks likely to plummet making the whole system unstable. It looks great on the weather maps though - a nice, perfect looking low.

The low is bad timing for those in Gisborne who had flooding just last week. I think Northland may also be pretty vulnerable to flooding - especially in eastern areas where the wind will blow the rain clouds in against the hills. If you have hills to the west of you then the chances of flooding increases with this storm. Likewise if you have hills to the east of you it will increase the chances of wind damage. I don't know how bad the winds will be in my home town of Te Aroha - a town that is very exposed to easterly gales. Severe gales are quite likely but I think I need to wait until the next round of data and computer models updates (this evening) before I'm more certain of wind speeds and potential damage. But at this stage I'd say gusts to 150km/h are possible most likely on Sunday morning. MetService are predicting 140km/h gusts also on Sunday morning.

For extra updates check out WeatherWatch's special Storm Page and of course our homepage too.

I'll also be posting storm updates via Twitter (as well as other random stuff!).

Philip Duncan

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