Severe thunderstorm watch Wellington, Wairarapa, Marlborough

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Severe Thunderstorm Watch

Valid to: 8:00pm Thursday 17 Jan 2013
Issued at: 9:35am Thursday 17 Jan 2013

SEVERE THUNDERSTORM WATCH

Issued by MetService at 09:35 am Thursday 17 January 2013
Valid until 08:00 pm Thursday 17 January 2013
This watch affects people in the following weather forecast districts:
Wairarapa
Wellington
Marlborough

Thunderstorms are expected to develop on and behind a southerly change that is expected to reach Kaikoura about midday and move over the southern North Island this afternoon. There is the possibility of some of these thunderstorms being SEVERE due to large hail (greater than 20mm diameter) and damaging wind gusts (110km/hr or more) occurring. Large hail can cause significant damage to crops, orchards, vines, glasshouses and vehicles, as well as make driving conditions hazardous. Wind gusts of this strength can cause some structural damage, including trees and power lines, and may also make driving hazardous. The risk of thunderstorms diminishes this evening and it is unlikely that SEVERE storms will continue beyond about 4pm in the south and 8pm in the north.

Issued by: Allister Gorman

This watch will be updated by: 02:00 pm Thursday 17 January 2013

Severe Thunderstorm Criteria

MetService uses the following criteria for severe thunderstorms in New Zealand:

Heavy rain (from thunderstorms):

Rainfall of 25 millimetres per hour, or more.

Large hail:

Hailstones 20 millimetres in diameter, or larger.

Strong wind gusts (from thunderstorms):

Gusts of 110 kilometres per hour (60 knots) or stronger.

Damaging tornadoes:

Fujita F1 (wind speeds greater than 116 kilometres per hour (63 knots)) or stronger.

Note: some tornadic systems such as funnel clouds, waterspouts and small land-based tornadoes are possible with thunderstorms that may not be classified as severe.

ENDS

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