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Some Rain, But Is It Enough?

Posted By Jo Pentreath | October 14, 2020

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

The region gets an A grade for hitting 100% of September’s average rainfall.  It was on the back of overachievers like the north and south of the region and also the Ruahine Ranges, where rainfall exceeded the month’s average, whereas the Heretaunga Plains on 78% and Tangoio on 73% were slackers in comparison.  It was a result full of promise for our groundwater, soil moisture and river flows – largely unfulfilled sadly.

Groundwater levels can’t seem to shake their below normal malaise and river flows averaged a paltry 56% of typical September levels.  It’s because soils were tight fisted with whatever water they got. Not so tight fisted that warm temperatures, egged on by bothersome westerlies, couldn’t wheedle out some of that moisture and leave soil moisture levels tracking on the wrong side of normal, particularly in Central Hawke’s Bay.

Prospects of rain are encouraging now that a La Niña is upon us and the Indian Ocean Dipole toys with turning negative.  Higher than normal sea level pressures are forecast to the southeast of us and lower pressures to the northwest, which should set up an easterly flow that will hopefully be moisture laden from higher than normal sea temperatures.  Rainfall should be near normal, if not above normal, in northern areas according to the seasonal forecast models.  Most pick near normal rainfall for the south too.  But a couple of rebels blink warning signs of a drier south should the higher pressures expected in the southeast entrench themselves across our southern boundary.

 

                                                                             September 2020 Rain Map

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