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SAM did it

Gisborne's near-drought situation is a combination of a dry 2019 and a random weather pattern called SAM for short.

SAM is the acronym for Southern Annular Mode, or Antarctic Oscillation (AO).

For most, 2019 is a distant memory but its weather record has left its mark.

Starting in mid-April, it had over five consecutive months of below average rainfall, with November also below average.

The year ended about 200 millimetres short of the 30-year (1981-2010) average.

Last year carried a soil moisture deficit into winter and only briefly got back to normal before it started accumulating another deficit.

There were just five decent rain amounts on seven days from June to the end of the year, and by early December the soil moisture deficit was back up to 132mm.

Last year, there were only 80 wet days (days of 1mm or more, according to MetService). This was well short of the 30-year average of 108 wet days.

This year picked up the dry trend.

There have been only 28.8mm so far and an outlook that offers no relief in the immediate future.

The soil deficit was just on the 140mm mark, which in past years has indicated imminent drought.

Meanwhile, the SAM weather pattern has made itself felt, with high rainfall and winds in the far south and dry conditions in the east.

The SAM is the ring (hence annular) of weather that endlessly circles the Antarctic — a belt which expands and contracts in no as-yet-determined pattern.

Since November, SAM has been in its negative phase (closer to Australia and New Zealand), which has meant dry and hot conditions in the east for both countries.

Since the start of the new year, SAM has swung into its positive mode, closer to Antarctica, which generally means more settled weather and light winds for us.

SAM has delivered floods and damage to the south and West Coast, while most of the North Island is now coloured red in the Hotspot map of the National Institute of Water and Atmospheric Research.

The latest projections for the next couple of weeks offer little hope of rainfall relief.

Tropical Cyclone Uesi is expected to veer towards Australia while a change to southerly conditions may bring some spots of rain to the Gisborne-East Coast region over Monday to Wednesday next week.