Yesterday New Zealand saw a severe thunderstorm form around Central Plateau and over the next week ahead, people are being warned to expect more heavy inland downpours forming across both islands.

WeatherWatch.co.nz says it's due to a slightly more humid air flow bringing 'thicker' air from the sub-tropics across the country.

Thicker air means it has more moisture in it - or humidity. It's not always the same as 'muggy' conditions which is when we have a very hot day with extremely high humidity and it feels like the tropics, as you can have high humidity when it's cold too, like a foggy morning in winter.

"So with higher humidity levels it means more drizzly and cloudy areas in the mornings, then warm to hot days with some afternoon cloud build-ups producing inland downpours, some with thunder.

"Most of these downpours look inland away from main centres but may still be near populated communities."

Next week sees the highest chance for this across inland areas of both islands with perhaps the main risk in the first half of the week. Keep up to date with the tax funded Severe Thunderstorm Outlook from Government forecaster MetService too.

"Despite this forecast New Zealand is still facing a mainly dry week ahead with drier than usual conditions for this time of year but these isolated downpours will also bring a little hit and miss relief to those that need it too."