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Northern NZ: “Unusual” risks for severe weather on Saturday

Normally when severe weather is coming in it’s fairly clear cut as to where the rain will go and where the winds will be. However when a deep low forms within 24 hours we must rely on computer guidance more than usual – then on top of that add a layer of knowledge from “previous experience” with similar rapidly deepening lows in the north.

With that in mind we see a fairly unusual set up for severe weather risks in Auckland on Saturday. The area that can produce severe weather covers anywhere from the Far North down to about Taupo. However the areas the could cause any flooding or wind damage look very localised.

This update is Auckland focused, for Auckland Civil Defence, however Northland, Waikato, Coromandel Peninsula, Bay of Plenty and East Cape all have similar risks as the low crosses from west to east during the day.

Rain likely develops before dawn in Auckland with the chance of a heavy downpour. As the morning goes on rain will cross the region with a mix of steady rain and some heavier and lighter falls – with a burst of heavy rain and isolated thunder possible towards the middle of the day as the end of the main rain bands moves through. The afternoon looks drier as winds turn southerly. has MODERATE confidence of rain in localised areas causing some flash or surface flooding.

With the low still deepening – and deepening further across the weekend – it makes it hard to pinpoint wind speeds and where any potential damage could be. At this stage we think generally the winds won’t be severe – but could be locally damaging within some of those torrential downpours or possible thunderstorms. Again – this looks localised. has VERY LOW confidence of widespread wind damage and LOW confidence of isolated wind damage.

Whenever you get two air flows mixing – a warm sub-tropical one and a cooler, drier, southerly – it’s a recipe for thunder. There is an ORANGE risk (moderate) for thunder in Auckland on Saturday, again it will be localised – and connects back to both the Rain and Wind sections above.

A wet Saturday morning with a few gusts and a few heavy downpours, then a drier afternoon and evening on the way – but with southerlies picking up and becoming stronger on the west coast. The southerly change behind this system may well be stronger than the winds before it.

This system is at the lower end of severity, but when a Low is actively deepening when it crosses over our most populated regions there is certainly a moderate potential for pockets of weather related issues.



Zelda Wynn on 22/05/2015 1:43am

Sounds like we should all prepare for stormy weather

People next to streams or in low lying areas be very aware of possible flooding!

Great updates WeatherWatch!

Guest on 22/05/2015 12:37am

Be unusual if the sun shone all day in a blue cloudless day or lightning flashing all over the sky for hours or snow falling.

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