This week's torrential rain has broken a 50-year-old national rainfall record.
National Institute of Water and Atmospheric Research (NIWA) meteorologists say 103 mm of rain that was recorded from 4 am to 5 am at Maungatapere near Whangārei on Monday is a new hourly rainfall record for a low elevation station.
The previous record was 100.6 mm recorded 56 years ago at Whenuapai in northwestern Auckland on February 16, 1966.
But NIWA Principal Scientist - Forecasting Chris Brandolino warns that more extreme weather events will become more common.
"A warming planet means that we expect to see more extreme weather events like this. In the future, it’s likely such events will become even more common and more extreme."
Brandolino says as well as the extreme downpour, around 3000 lightning strikes were recorded in Northland on Monday morning.
He says the thunderstorms that were created by a low-pressure system in the Tasman Sea increased the rate of rainfall, as well as marine heatwave conditions around the country.
Brandolino says the current weather system that caused significant flooding in Auckland and Gisborne, has been particularly slow at moving because it has been blocked by an area of pressure to the southeast.
Brandolino explained the hourly rankings at NIWA are calculated from top-of-hour to top-of-hour.
"The maximum 60-minute total at Maungatapere on Monday morning was even higher at 123.2 mm from 3:30 am to 4:30 am."
"Because off-hour totals are not routinely calculated or cited in records, we can’t definitively confirm whether this would represent an off-hour record, although it did exceed the previously known off-hour record of 109.4 mm at Leigh, Auckland in May 2001," Brandolino said.
He said the new record was not the highest-ever hourly rainfall but the highest for a low elevation station, which is up to 500 metres above sea level.
The highest-ever record of 134 mm in an hour is still held by the Cropp Waterfall station near Hokitika on January 8, 2004.
He says the record went through rigorous quality checks to confirm its validity.
"With near-instant access to data from our weather stations, you might wonder why it’s taken us the week to announce the record. This is because any new records go through a rigorous quality checking process, where we review the data, compare it to existing rankings and carry out a site inspection to confirm the quality of the data."
