Recent rainfall and current soil moisture conditions:

In the North Island, the greatest rainfall amounts over the last seven days fell in the western North Island, mainly in Taranaki, Waikato, portions of the Manawatū, and the eastern Bay of Plenty, where 100 to 150 mm of rain fell. Generally 50 to 100 mm of rain fell across coastal Taranaki, remaining Waikato, much of the Manawatū, interior Northland, about the Tararua Range, and the foothills of Hawke’s Bay. Generally 10 to 30 mm of rain fell in the Bay of Plenty around Whakatāne, the Far North, Wellington and the Wairarapa, and Gisborne, with some portions of Hawke’s Bay recording less than 10 mm. Elsewhere, generally 30 to 50 mm of rain fell across the North Island. Soil moisture levels remained the same or increased across most of the North Island, with the greatest increase across Northland, Auckland, the Manawatū, western Wellington, the Waikato, and the western Bay of Plenty. Soil moisture levels decreased in eastern Wellington and about the Māhia Peninsula. The driest soils across the North island, when compared to normal for this time of year, are found around Hastings and coastal Wairarapa. The wettest soils for this time of the year are generally found in the Auckland region and the west coast of lower Northland.

No hotspots are currently located in the North Island. However, as of 28 October, the New Zealand Drought Index (NZDI) map shows that drier than normal conditions are currently found in the Hastings area.

In the South Island, 100 to 200 mm of rain fell in the past week across most of the West Coast with pockets greater than 200 mm. Western Tasman, western Southland, interior Otago, and the Canterbury foothills generally saw 50 to 100 mm of rain. Coastal Otago, the Canterbury Plains, most of Marlborough, eastern Tasman and Nelson districts generally received 10 to 30 mm of rain with a few pockets seeing less than 10 mm. Elsewhere in the South Island, remaining areas generally saw 30 to 50 mm of rain.

The driest soils across the South Island, when compared to normal for this time of the year, are found in Canterbury and in Marlborough around Blenheim, while the wettest soils for this time of the year are generally found in interior Otago.

No hotspots are currently located in the South Island.

As of 28 October, the New Zealand Drought Index (NZDI) map shows that drier than normal conditions are currently found in the Hastings area. Please note: some hotspots in the text above may not correspond with the NZDI map. This difference exists because the NZDI uses additional dryness indices, including one which integrates the rainfall deficit over the past 60 days. Changes are therefore slower to appear in the NZDI compared to soil moisture anomaly maps that are instantaneously updated.

The week ahead:

For the North Island, a weak cold front will bring light rain or drizzle on 31 October, followed by high pressure from 1 to 5 November, with generally dry conditions overall. Low pressure approaches 6 November with light to moderate rain for the North Island. Weekly rainfall total will be up to 20 mm across most of the North Island, with isolated totals of 20 to 40 mm in the central North Island. Elsewhere, some parts of the east coast may record little to no rain.

Due to the expected rainfall in the next week, a decrease in soil moisture levels are likely for most of the North Island. The area of dryness around Hastings may start to approach hotspot status.

For the South Island, a weak cold front clears on 31 October with light rain, followed by high pressure from 1 to 3 November, bringing several days of mostly dry weather. A few cold fronts move into the south and west of the South Island with rain late on 3 November through 5 November, followed by more widespread and heavier rain next Thursday, 6 November. Weekly rainfall total will be 50 to 100 mm for the West Coast. 10 to 30 mm of rain is expected for interior Otago, western and coastal Southland, and the western Tasman district. Elsewhere, less than 10 mm of rain will fall, with many parts of the east coast of the South Island recording little to no rain.

Due to expected rainfall in the next week, soil moisture increases will be possible in the western South Island. Elsewhere, expect a decrease in soil moisture.

Long-term outlook (through late-November):

• The drier (25th percentile) rainfall scenario shows below normal rainfall across all of New Zealand, with very dry conditions for the east of both the North Island and South Island. • The middle (50th percentile) rainfall scenario show a dry signal for the east of the South Island and the lower North Island.

• The upper (75th percentile) rainfall scenario show a wet signal for the upper and western South Island and for the east and north of the North Island, with a dry signal for Otago.

Background:

Hotspot Watch: a weekly advisory service for New Zealand media. It provides soil moisture and precipitation measurements around the country to help assess whether extremely dry conditions are imminent.

Soil moisture deficit: the amount of water needed to bring the soil moisture content back to field capacity, which is the maximum amount of water the soil can hold.

Soil moisture anomaly: the difference between the historical normal soil moisture deficit (or surplus) for a given time of year and actual soil moisture deficits.

Definitions: “Extremely” and “severely” dry soils are based on a combination of the current soil moisture status and the difference from normal soil moisture (see soil moisture maps at https://www.niwa.co.nz/climate/nz-drought monitor/droughtindicatormaps)

Hotspot: A hotspot is declared if soils are "severely drier than normal" which occurs when Soil Moisture Deficit (SMD) is less than -110 mm AND the Soil Moisture Anomaly is less than -20 mm.

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