A very narrow but intense area of weather lies just off the western coastline of Northland, Auckland and Waikato as of late Saturday morning and is very slowly tracking eastwards towards land. It will cross over the upper North Island over Saturday PM and then across Sunday. There are currently (as of near 11am) thunderstorms just west of the North Island coupled with some intense rain.

However the heaviest downpours and thunderstorms are mostly confined to an area no wider than just 50km west to east across. This is not an overly major widespread outbreak, rather it’s a narrow but very active slow moving front.

Outside of this narrow but active area of weather there are clouds and more normal isolated showers, some perhaps a little heavy.

The sometimes brisk nor’east flow is also helping bring sunny spells to the upper North Island ahead of this very narrow but active front – but the front is moving into this air flow so eventually the downpours will cross places like Auckland – the front may also break up or change intensity as it crosses Northland and Auckland later today. Saturday may not be as wet as some thought it might be but the risk for heavy downpours increases as Saturday wears on.

MAIN FEATURES:

• An upper level cold pool corresponding to the weak low pressure system hugging the West Coast is bringing unstable conditions this weekend, leading to a narrow and fairly small risk zone but one that has a high probability of very heavy downpours and thunderstorms.
• This risk is mainly over the western and upper North Island
• Today severe thunderstorms are possible in Taranaki, Tasman and Nelson. They will be isolated.
• They are also possible in Northland, Auckland and maybe Waikato later today or in the evening, again isolated but highly possible. 
• Heavy short-duration downpours are possible in these areas. Maximum rainfall rate is expected to be 25-40mm which can bring localised flooding.
• The area of high thunderstorm probability will move eastwards over the upper North Island on Sunday (like Bay of Plenty) with reduced intensity behind it.

– WeatherWatch.co.nz (an official IBM Business Partner)