Heavy rain on January 27 was the wettest day on record in Auckland, New Zealand, with a number of weather stations recording over 200mm of rain in 18 hours. The weather station in Oakland (Albany) recorded 260.6 mm of rain between 3:00 and 21:00, and in some parts of the city more than 150 mm of rain fell in three hours, which led to severe flooding.
The maximum hourly accumulations in the city reached 50-70 mm and persisted for several hours. These amounts represent almost 300% of the normal January rainfall and broke the previous monthly record of 206mm in 1986. This is close to central Auckland’s record monthly rainfall of 420mm in February. 1869 (based on historical research by Anthony Fowler in 2020). More rain is expected, total rainfall could reach or even break the monthly record by the end of the month.
In addition to heavy rain, Westport on the South Island recorded its hottest day on record when temperatures hit 28.7°C on January 28. Sea Surface Temperatures (SSTs) around New Zealand have consistently been above average over the past few months, especially throughout January, which contributed greatly to last week’s high rainfall as well as an overall very rainy month. The heat allows more moisture to be retained in the atmosphere, which allows for much more precipitation in a short period of time, in this case, in just a few hours, almost three times as much precipitation falls as in a typical January.
Current estimates show that SSTs off the west coast of New Zealand were about 2-3°C above normal during January. Several other factors that contributed to heavy rainfall over the North Island included La Niña, a saturated atmospheric column, and a low-level jet stream heading for the island.
There has not yet been a named storm in the UK this 2022-23 season, despite often wet and windy conditions in the fall and early January. Because the naming system was put in place in 2015–2016, the fewest number of named storms prior to February 1 was three. However, winds will increase from Tuesday to Wednesday this week, especially in Scotland, with gusts likely to reach 60-80 mph in the far north, bringing frequent winter showers. Whether that will be enough to justify the named storm remains to be seen.
