MetService has issued a severe thunderstorm warning for the Auckland region on Tuesday.
"These thunderstorms are expected to be accompanied by very heavy rain and large hail," a spokesperson says.
"Very heavy rain can cause surface and/or flash flooding about streams, gullies and urban areas, and make driving conditions extremely hazardous.
"Large hail can cause significant damage to crops, orchards, vines, glasshouses and vehicles, and make driving conditions hazardous."
The Ministry of Civil Defence and Emergency Management warns that as the storms approach, people need to:
- Take shelter, preferably indoors away from windows
- Avoid sheltering under trees, if outside
- Move cars under cover or away from trees
- Secure any loose objects around your property
- Avoid streams and drains as you may be swept away in flash flooding
NIWA is warning motorists to take care on the roads, as localised downpours hit.
"Could be a bit of an active day for the upper North Island with towering TCu (towering cumulus) popping this early. Scattered showers & t-storms likely today," a spokesperson said on Twitter.
"Take it slow if you happen to drive through one."
It's also told boaties to get off the water immediately.
"If you know anyone on the water, tell them to get out. You're the tallest thing on the water."
It's also cautioning of cloud-to-ground lightning west of Auckland's CBD, due to the risk of being struck.
MetService says there is a "moderate thunderstorm risk", and isolated thunderstorms are possible until late evening.
"Today we have the equivalent of a surface low moving across the North Island, only at higher levels. This is upper level low is forecast to move over the upper North Island today as sea breezes develop over the land this afternoon," MetService says.
"As westerly sea breezes from the west coast and easterly sea breezes from the east coast converge (or meet), they force the air upwards. From this upwards draft a small 'fair weather' cumulus cloud or a thunderstorm can form, depending on how strong and how high the upwards draft reaches."
The weather has been picked up by locals, confused by the combination of heavy rain and blue skies.