An enormous high pressure zone will next week create a significant set up in the New Zealand area, which could lead to severe gales and rain heavy enough to causing flooding in some pockets.

The powerful high will get into 1040hPa range and the size of the high will extend well up into the tropics. The anti-cyclonic flow will then encourage a North to North Easterly flow down over New Zealand, which will add +14 degrees to overnight temperatures in some areas (for example, Hamilton is -1C tonight but +13C by Tuesday night).

At the same time, an area of low pressure in the Tasman Sea will crank those winds up even further – and help drag down more rain. The powerful big high will then stand in the way of that rain and low pressure area being able to move through across NZ. This then does two things: 1) Create a windy “squash zone” between the high and the low, which may see gales eventually gust 70 to 100km/h. 2) The high slows down the rainmakers feeding down from the north, which increases rainfall totals and leads to possible slips and flooding.

For now, Nelson and Bay of Plenty perhaps look to be most exposed with rainfall totals over the coming 7 to 10 days varying between 100 and 200mm.

This is an evolving situation – keep an eye on your local 10 day forecast from WeatherWatch.co.nz and/or RuralWeather.co.nz for more details on rainfall totals and windspeed in your area.

• WeatherWatch.co.nz / RuralWeather.co.nz