Hardly any rain, El Nino building

This map from Niwa shows severely dry areas at the top of the East Cape and the whole of the Gisborne Flats as moderately dry, though groundwater levels in many places are still high. Picture supplied

The Gisborne area has now had 50 days without significant rain — another indication of the building El Nino.

Historical records show no dry spell has started this early in the year.

The last  decent drop of rain was 35.7 millimetres on July 21.

In 50 days Gisborne has had a total of a fraction over 40mm, with only a handful of days amounting to more than a wetting of the grass.

So far this month has registered just a touch of damp in the rain gauge — point six of a millimetre as of yesterday.

With all the rain of this year, the daily soil moisture deficit was at zero at the end of July.

Since then, sunny days and the lack of rain have seen a deficit develop by a couple of millimetres a day.

Today the deficit is just over 40mm.

The switch from wet to dry has also been accompanied by a change in the wind pattern.

Easterlies and southerlies dominated in the earlier part of the year, but a noticeable swing back to westerlies and northerlies began in July.

Clear skies have also meant chillier mornings and more frosts, even though they were not as severe as those of the ‘80s.

Last month had 14 mornings where the ground temperature fell below zero, while so far this week there have been five below-zero grass temperatures.

This has meant the average daily temperatures have been dragged down, despite the sunny daytimes.

Daytime highs in the first week of this month have averaged almost 18 degrees — a whole degree warmer than the 30-year mean (1991-2020).

But the mean minimum has been two degrees below normal, at 5.2.

Examining the historical weather records held in the National Archive, Gisborne’s driest approach to summer would appear to be 1972, when just 114mm fell over the four months from August to the end of November.

Other dry spells in the run-up to summer occurred in 1964 and 2008.

The driest year looks to have been 1994, which had just 1.6mm in December and the year’s full rainfall total jugt 701mm.

The latest measurements for the Southern Oscillation Index, as taken by combined United States agencies and their satellites, show the index is steadily climbing and the El Nino strengthening.

Daily climate maps from our National Institute of Water and Atmospheric Research (Niwa) show the top of East Cape and Gisborne Flats are drying rapidly, although groundwater levels in many places are still high.

Eastern areas down the coasts of both islands are drying, with El Nino’s effects being felt the most in Central Otago where the Standard Precipitation Index is indicating “extremely dry”.