Thunderstorms to be followed by relative calm

12 August 2019

After a weekend that saw heavy rain, heavy snow and severe thunderstorms affect parts of the country, MetService is forecasting the weather to calm down by the middle of the working week. However, thunderstorms remain in the forecast for parts of the country today.

MetService Meteorologist Peter Little comments, “On Sunday morning a Severe Thunderstorm Watch was issued for northern New Zealand, and on Sunday evening a line of Severe Thunderstorms was identified approaching Auckland and Warnings were issued. These severe thunderstorms brought damaging wind gusts that blew down fences, lifted roofs, including damaging part of The Cloud on Auckland’s waterfront, and toppled over shipping containers at the port. On Monday morning another Severe Thunderstorm was identified coming onshore over New Plymouth, which resulted in a damaging tornado and large hail.”

The threat of squally thunderstorms remains over much of the North Island and upper South Island today, and a Severe Thunderstorm Watch has been issued. Any thunderstorms that occur will likely be accompanied by localised heavy rain, hail, wind gusts of 110 km/h or more, and possibly a small tornado. See the Thunderstorm Outlook for more detail.

Little explains, “One of the driving forces of these thunderstorms has been very strong upper level northwesterly winds extending from Queensland in Australia across the Tasman Sea and over northern New Zealand. This current of strong winds is also known as a subtropical jet stream. Our weather balloon sounding released from Whenuapai in Auckland on Sunday recorded a maximum wind speed of 380 km/h at 35000 feet. This is around the cruising altitude of large airliners, and this tail wind means fast flights from Brisbane to Auckland, but slow going on the return journey.”

A lighter southwesterly flow over the South Island brought showers into the far south this morning, but many places started the day clear and crisp. “Mount Cook Aerodrome dipped down to a frigid -8.8°C this morning,” adds Little.

The cool and showery southwesterly flow strengthens and spreads over all of New Zealand on Tuesday, with gales likely in exposed places. Snow showers are also expected above 300 metres over southern New Zealand.

Southwesterlies and showers gradually ease during Wednesday and Thursday, but a front brings heavy rain to the West Coast and far south of the South Island on Friday. A low is expected to develop on this front as it moves northwards on Saturday, spreading rain over much of the country.

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