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El Nino is here

Posted By HBFA | June 23, 2023

*Date: 16th June

May was enjoyably balmy and reasonably dry. The region had 70% of average May rainfall. Some areas, such as the Heretaunga and Ruataniwha Plains and southern Hawke’s Bay, didn’t see that much though, instead getting roughly 50% or less. It’s three months now of below normal rainfall for the Heretaunga Plains.

Most of May’s rain fell in the ranges, feeding the headwaters of our rivers and keeping flows during May near or above normal. Soil moisture levels remained high through the month and groundwater levels were mostly near or above average for the time of year. Air temperatures were a couple of degrees warmer than usual, helped by above average sea temperatures. Soil temperatures were also warm for May and finished the month on 12°C on the Plains and 11°C in the ranges.

If you haven’t heard, the El Niño, which was predicted to develop this winter, has materialised already and holds potential to be a strong event. A likely partner is a positive Indian Ocean Dipole, which typically suppresses rainfall over much of Australia and can similarly influence our region’s weather.

There is a reasonable chance June’s rainfall will be near or above average but July to September could swing the other way and be near or below normal. West or southwest winds could prevail thanks to higher than usual sea level pressure west of the country, which may in fact extend across us, and lower pressure to the east. Sea temperatures might peg back to near normal levels around our region and air temperatures too. The seasonal forecast models don’t unanimously agree that a run of dry weather is looming but the majority lean that way so it’s worth having a plan should that be the case.

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Percentage of Normal Rainfall

 

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

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