A meteorological bull’s eye is painted upon the upper North Island as ex-tropical cyclone Hale bears down on regions already well soaked from New Year’s rain.
Despite bearing the title of “cyclone” only briefly overnight, Hale has civil defence and weather experts casting a wary eye at a system likely to take on a vicious second life as an intense low-pressure system bearing significant rainfall and wind potential.
WeatherWatch director Phil Duncan said hopes are high the system will move through quickly, possibly within 24 hours, and have a localised effect rather than widespread impact across the island.
“But these things, they can be like famous celebrities that once were good looking and then are not. This was a baby cyclone compared to the likes of Drena [1997], but when they form into an ex-tropical cyclone storm they get a second personality with potential to be a big rainmaker event.”
At this stage WeatherWatch has the system tracking to the tip of Coromandel Peninsula at 7pm on Tuesday, arcing across East Cape then cutting a zigzag down through Hawke’s Bay, into Wairarapa, and exiting across the Pacific.
“My feeling is it will not be as bad as past cyclones and it will move through fast in maybe 18 hours with potential for flooding in Coromandel, Gisborne and East Cape.”
Western Bay of Plenty and rural North Auckland may also face some flood risk.
The resulting rainfall could be hitting regions including Western Bay of Plenty and Coromandel that have already experienced well over a month’s rainfall in the past week, with slips and storm damage laying a dampener on many holidaymakers’ plans.
But Duncan said for farmers this summer has been something of a pastoral bonanza, with most parts of the country receiving useful to significant levels of moisture that have gone hand in hand with warm temperatures to guarantee strong summer growth.
“Farmers I have spoken to are doing cartwheels. Many have experienced some very tough dry summers in the North Island in past years, and South Island farmers are pretty happy too.”
Central Otago, one of the country’s driest areas, is presently among the wettest, sharing record high soil moisture levels with Western Bay of Plenty.
“Southland is having a good run, and even Canterbury has had some good showers.”
Wairarapa is likely to catch the hook of Hale’s exit and is the one region in the country that could do with additional moisture that it would bring, possibly as much as 60mm.
A recent analysis of cyclones by Surfline meteorologists identified a decline in cyclone occurrence in the past 20 years, compared to 1969-2000 in the Australian region.
Australian Bureau of Meteorology indicates from 1969-2000 the long-term average of cyclones was 11 a year. Since then, that has dropped 18% to nine on average.
Researchers have noted they also appear to be getting stronger and are forming in new places.
Duncan said these findings have been supported by other work. Understanding the reasons can be fraught due to the relatively short period for which data has been kept.
However, he said increased atmospheric instability due to climate change could help explain why cyclones may be less frequent.
“It is a bit like lacking a smooth table top to spin a top on: if it’s rougher, it’s harder to get the top spinning.”
He said of greater concern are the atmospheric “rivers” of moisture that have been part of the past two NZ summers, channelling vast amounts of tropical temperature air flows down across the country.
He still forecast that NZ will see some extended dry periods this summer – something that will be welcome by both farmers and holidaymakers.
Updates here on Hale’s progress.
