I normally use this space to describe the previous month’s weather and the outlook. The recent brutality of ex-Tropical Cyclone Gabrielle made me reconsider and even made me forget what January was like. But having looked back, I think January is worth briefly mentioning before looking at the extraordinary event that was Gabrielle.
January was the region’s sixth consecutive month of above normal rainfall. The region had approximately 400% of January’s long term average however it was closer to 500% on the Heretaunga Plains, in the Kaweka Range and Tangoio and Esk areas. From Tangoio southwards, January 2023 was the highest recorded January total at all but a handful of our rainfall sites. River flows had a similar percentage increase above average, most of our groundwater sites hit new record January levels and soil moisture levels across the region were at field capacity or saturated.
We were soaked and then came Gabrielle. February immediately became our seventh consecutive month of above normal rainfall. Tangoio and Esk swiftly exceeded 450% of average February rainfall, with one site hitting 700%. It’s where we recorded 500 mm of rain, approximately half a year’s worth, in 24 hours and half of that was in 6 hours. We have gauges dotted across the region that recorded 400-500 mm during the event – from north of Mahia to the hills along the south coast and across to the western ranges. At least half of our sites recorded their highest 6 to 24 hour totals. Those that existed during Bola in 1988 experienced higher intensity rainfall during Gabrielle. More than half of our river level sites recorded new highs.
We expect the very windy conditions meant our gauges didn’t capture the full extent of the rain and they likely missed some localised heavy falls. We’ve had reports of 700-800 mm in places. So we have put out a call for people to share their rainfall totals with us along with the location. We’ve set up an email, firstname.lastname@example.org, for that purpose and we’d welcome you to use that.
Despite the La Niña weakening, it’s influence lingers and makes the outlook for the next few months bleak. We still expect an easterly flow to be a key feature, bringing the likelihood of above normal rainfall and warmer than usual overnight temperatures if not during the day. Potential remains for an El Niño to develop later in the year however after so many months of wet weather, any risk of drier than normal weather down the track seems hard to take in.
Percentage of Normal Rainfall
Dr Kathleen Kozyniak
Principal Scientist Air
Hawke’s Bay Regional Council