Today's torrential rain is a "weather traffic jam", not unlike an Auckland morning during March Madness, says Niwa meteorologist Ben Noll.
It's an autumn trifecta for weather-induced misery: strong and slowing moving low pressure, deep tropical moisture, and a blocking ridge of high pressure to the south.
The strong and slow moving low pressure is the driving force behind all of the adverse weather.
The deep tropical moisture is an atmospheric moisture source from the Indian Ocean, Coral Sea, and Pacific Islands, known as an atmospheric river.
And the blocking ridge of high pressure is high pressure building to the south and east of New Zealand, encouraging slow movement of the "Tasman Tempest", effectively preventing it from moving over the next several days, says Noll.
The weather is expected to slowly settle across most of New Zealand by the middle stages of next week. By late next week and into next weekend, high pressure may be the dominant weather player across the country, bringing plenty of dry weather and gradually warmer temperatures.
Warm and dry "beach-type" weather may actually be the flavour into late March as well, which will be welcome after this week's extremes, said Noll.