NOTES ON THE WEATHER FOR APRIL 1969

General—This was a cool month with several periods of strong west or south-west winds. Most of the North Island and the north, east, and south of the South Island were affected by these winds. About average rainfall in many areas relieved the dry conditions which had prevailed through March. Pasture growth was good in most places but in some areas the temperatures were too cold for the rain to have much effect on growth.

During the period 8 to 10 April a strong cold south-westerly airstream covered the country. A tornado on the 8th caused property damage in Levin and the high winds carried some of the debris it produced over the Tararua Ranges to a point some 15 miles away in northern Wairarapa. At the same time strong winds also disrupted communications in southern Hawke’s Bay and northern Wairarapa bringing down telephone wires and causing some sections of road to be temporarily closed because of high wind speeds. Early on the 10th a small tornado occurred in a western suburb of Auckland causing a small amount of property damage.

Rainfall—Most of the country received more than three-quarters of the normal monthly rainfall and parts of Wairarapa, coastal Marlborough, and north Westland and Buller had twice the average amount. However, in eastern Northland, northern Gisborne, and over an area of South Canterbury and northern and Central Otago the rainfall was well below average, being less than one-quarter of the normal value in a few places. In the north of the Gisborne district it was the second successive dry month.

Temperatures—Except in parts of Canterbury, the mean temperature was below average over the whole country. In parts of Westland it was 3 degrees below normal and over a large part of the remainder of the country it was 1 to 2 degrees below. Snow fell to low levels in parts of Otago and on Mount Egmont during the period 8th to 10th.

Sunshine—Most districts were favoured with above or near average sunshine. Parts of south Westland and inland Otago had a 30 hour surplus while Westport had 37 hours less and Thames 44 hours less than their normal amounts.

Weather Sequence—A developing depression over the central Tasman Sea began to move slowly south-eastwards towards the South Island on 1 April. Rain fell in most parts of the country on the 2nd as the depression and its associated frontal system approached. The depression continued to move south-eastwards crossing the South Island on the 3rd with rain falling over most of the country. A south-westerly airstream prevailed on the 4th as the depression moved away, and the rain became scattered. The rainfall associated with this depression relieved drought conditions which had persisted in some areas through March.

On the 5th a ridge of high pressure lay over central New Zealand but some scattered areas of rain persisted in the north-east and some heavy falls occurred in south Westland and Fiordland. During the following day a cold front moved north-eastwards over the whole country and a disturbed south-westerly airstream prevailed behind it. Rain fell in many places on the 6th and 7th and early on the 8th a tornado passed through Levin causing damage to several properties. The south-westerly airstream became very strong on the 8th after the passage of an active cold front. Gale force winds were reported in many parts of the North Island and east of the South Island on the 8th, 9th, and 10th, and some very high seas affected the east coast of the North Island from Wellington to Napier. Many of the ranges of the South Island and central and southern North Island received their first snow cover of the winter.

Disturbed west or south-west conditions continued until the 15th with some heavy rain occurring in the south and west of the South Island and some rain at times in central and western parts of the North Island. A thunderstorm affected parts of Dunedin early on the 14th, and gale force winds occurred in exposed eastern South Island districts and in many North Island areas.

After the passage of a weak cold front on the 15th, an anticyclone moved eastwards from the Tasman Sea on to New Zealand and mainly fine weather prevailed on the 16th and 17th.

A complex depression, which began to form in the western Tasman Sea on the 16th, was moving towards the North Island on the 18th and rain fell over the whole of the North Island and north-east of the South Island. The depression moved slowly over the North Island from the 19th to 21st with rain in places. During this period a ridge of high pressure extended over the South Island where mainly fine weather prevailed.

Disturbed westerly conditions returned late on the 21st with the advance of a cold front on to the South Island. Widespread rain occurred in western and central parts of each island on the 22nd. A cold front which had moved on to the South Island late on the 22nd developed a depression which moved over the north of the South Island on the 23rd giving rain over most of the country. South-westerly conditions prevailed on the 24th and 25th. By the 26th an anticyclone from the Tasman Sea brought an improvement and mainly fine weather prevailed over the country on the 26th and 27th. By late on the 27th rain had started in the south and west of the South Island ahead of a further cold front which crossed the country on the 28th. A ridge of high pressure developed behind the front giving clearing weather but showers persisted in the north-east and south-west of the country. On the 30th the ridge of high pressure had moved north-eastwards to extend over the North Island and a cold front was moving over the South Island accompanied by a southerly change and showers.

J. F. GABITES, Director.
(N.Z. Met. S. Misc. Pub. 107)

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