Seasonal forecast predicting grim rainfall outlook

Posted By HBFA | August 16, 2021

Dr Kathleen Kozyniak
ncipal Scientist Air
Hawke’s Bay Regional Council

Last month I was singing the praises of June’s rainfall.  I’m lamenting July’s.  Truth be known, it was woeful, particularly on the Heretaunga and Ruataniwha Plains, where only 21% of average July rainfall fell. The region’s south coast wasn’t much better on 26%.  At least the main ranges got to about 70%, not that it left our rivers in great shape. They averaged 49% of typical July flows.   Groundwater levels wallowed in the below normal category so June’s good rainfall didn’t make much of a dent and July’s won’t have helped.

Thankfully July’s soil moisture levels held up. They were at median levels for the time of year on the Heretaunga Plains and areas north of Napier.  They weren’t so good to the south and west of the Heretaunga Plains, where some sites toyed with the lowest 10th percentile of readings for the end of July. Soil temperatures ended the month ranging from 7°C to 10°C and daytime temperatures were almost a degree warmer than average.

There are a couple of factors that point to good rainfall in the coming months but sadly the seasonal forecast models point their fingers in the other direction.  A negative Indian Ocean Dipole event is underway which can enhance our prospects of spring rain. There is a real chance of a La Niña developing during spring and staying for summer, which would normally bode well if we hadn’t had a drought in the last one.  The seasonal forecasts though are almost unanimously saying to expect below or near normal rainfall over the next three months. That’s due to higher than normal sea level pressures around our region and the winds taking on a northwest flavour. Hopefully the competing factors tussle it out and rainfall is the winner on the day.

Percentage of Normal Rainfall

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