Heavy Rains Unlikely to Alleviate North Island’s Unusual Summer Dry Spell

MetService has issued “orange” heavy rain warnings for Coromandel and areas north of Gisborne, effective until late evening.

Niwa forecasters indicate that the anticipated rain and humidity across the North Island this week will not counteract the unusual widespread dryness.

Dry conditions are expected to persist through February and into early March.

Despite heavy downpours affecting parts of the North Island, meteorologists report that these rains will not mitigate the unusual and extensive summer dryness that has taken hold across New Zealand. Moreover, significant rainfall relief is not expected in the coming weeks.

MetService has issued orange heavy rain warnings for the Coromandel Peninsula and Gisborne, north of Tolaga Bay, until late today. Over the past 24 hours, the Coromandel’s Pinnacles has already received 200mm of rain.

MetService meteorologist Katie Hillyer explained that the current weather system is bringing muggy conditions to the North Island. “Warm, humid air combined with extensive cloud cover acts like an insulating blanket, leading to warmer nights and uncomfortable sleeping conditions this week,” she said.
The weather system is expected to move south overnight, with 80mm to 100mm of rain forecast for the Tasman ranges between 9pm tonight and 7am tomorrow. “Thunderstorms are also possible on Tuesday afternoon and evening, affecting areas from Canterbury down to Southland, as well as Westland through to Buller,” Hillyer added. “Cloudy and wet conditions will dominate much of the country until Thursday and into Friday, when a high-pressure ridge is expected to push out the humidity and bring in fresher air.”

However, this influx of moisture is unlikely to reverse the drying trends that have caused significant soil moisture deficits across most of New Zealand. Niwa’s Drought Index indicates that large areas of Taranaki, King Country, and southern Waikato have entered meteorological drought, with most of the western North Island experiencing dry to extremely dry conditions.

Niwa meteorologist Chris Brandolino noted that the most parched regions are unlikely to receive much of this week’s rainfall. The lack of rain is further exacerbated by high rates of potential evapotranspiration—the amount of moisture lost to the atmosphere each day. Brandolino estimated that areas in Waikato and Northland have been losing 5mm to 6mm of moisture daily over the past two weeks.

“If we’re losing five to six millimetres of moisture to the atmosphere daily, it would take 50 millimetres of rain to offset those losses, and we’re not going to see that this week,” he said. “Unfortunately, the outlook for the next two weeks shows limited opportunities for rain, with unusually dry conditions expected to persist through the remainder of February and into early March.”

Niwa’s 35-day outlook also highlights a risk of “very dry” conditions continuing in Taranaki and along much of the South Island’s West Coast. “There may be some change as we move deeper into autumn, but as we conclude meteorological summer, there’s no indication of a significant shift in weather patterns to bring substantial rainfall,” Brandolino added.

This prolonged dry spell is concerning for farmers in affected regions and for fire crews, as high fire danger is currently being observed in parts of Northland, Taranaki, Manawatu, Tasman, Canterbury, Otago, and Southland. Meanwhile, Auckland’s dam levels are slightly below average for this time of year but remain around 70% full.

MetService Meteorologist Katie Hillyer notes, “Over the past 24 hours, the Pinnacles on the Coromandel Peninsula has recorded 200mm of rainfall. Even for this mountainous station, that’s an impressive amount.” Additional rainfall of 70-90mm is expected in these areas today.
High humidity will also dominate the North Island this week. “The combination of warm, humid air and extensive cloud cover acts like an insulating blanket, leading to warmer nights and potentially uncomfortable sleeping conditions,” explains Hillyer. Rotorua exemplifies this trend, with just a 2°C difference between yesterday’s maximum temperature and this morning’s minimum. Whanganui and Hawkes Bay are also in the spotlight, with temperatures expected to soar above 30°C in the coming days—a stark contrast to the cooler summer experienced in the east so far.

Overnight, the focus will shift from the northeastern North Island to the South Island, as rain associated with a low-pressure system from the Tasman Sea moves in. The Tasman District Ranges have been upgraded to an Orange Heavy Rain Warning, with 80-100mm of rain expected between 9pm tonight and 7am tomorrow. A Heavy Rain Watch is also in place for the Richmond and Bryant Ranges. By tomorrow morning, rain will spread to the eastern parts of the South Island, bringing much-needed moisture to some parched areas.

Hillyer also warns of potential thunderstorms: “On Tuesday afternoon and evening, Canterbury down to Southland, as well as Westland through to Buller, could see thunderstorms develop.” Rain will continue to affect much of the country through Thursday, with today and Tuesday being the most intense days.

“Cloudy and wet conditions will dominate most of the country until Thursday and into Friday,” says Hillyer. “A ridge of high pressure will then begin to push out the humidity, bringing fresher air and a welcome change to the muggy weather.”