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La Niña Present

Posted By Jo Pentreath | September 18, 2020

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

August was a great end to winter if you like conditions relatively warm and dry.  The lack of rain wasn’t ideal though, amounting to roughly half the long-term average for the month across the region.  For areas such as the Heretaunga Plains, the Ruataniwha Plains and the south coast, which didn’t even make it to 50% of normal rainfall, it is the second consecutive month of falling short of the long-term average.  It seems that a wet June was the only respite from low monthly rainfall totals since spring last year.

Despite that, soil moisture is holding up on the Heretaunga Plains, where it remains at median levels for the time of year.  Not so on the Ruataniwha Plains, where levels have dipped below average and are toying with the lowest 10th percentile of readings for late August.  The month’s air temperatures were warmer than usual and soil temperatures ended August in double figures – reaching 11°C on the Plains.

The odds of a weak La Niña developing in spring has increased and it’s helped us not get too concerned yet about a couple of months of low rainfall, though the seasonal forecast models, like last month, are very mixed. Some predict wetter than usual conditions and others drier.  Very few predict average spring rainfall!  However, the general impression is that we may continue with a predominantly westerly flow during September, after which easterlies may feature more strongly.  That makes us hopeful that spring rainfall we be at least near normal, as an easterly wind direction holds more promise of the region getting some decent rain. But it is worth noting the lack of consensus amongst the seasonal forecast models.  We have warm sea temperatures around the region currently and they should continue, which should help keep our spring air temperatures warm too.

 

August 2020 Rain Map

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