Thunderstorm Outlook
Issued at 7:42am 24/10/2021
Valid from 7:42am 24/10/2021 to 1:00am 25/10/2021
A front will move slowly southwards over Northland today, with scattered rain affecting many parts of New Zealand. Behind the front, scattered showers are likely to develop over Northland this afternoon and early evening from cloud buildups. There is a low risk of one or two of these showers developing into thunderstorms about eastern and inland Northland this afternoon and evening (as indicated on the chart). If any thunderstorms do develop. they will produce localised heavy rain. No other thunderstorms or significant convection expected over New Zealand today.
Issued at 8:03pm 24/10/2021
Valid from 1:00am 25/10/2021 to 1:00pm 25/10/2021
No thunderstorms or significant convection expected during this period.
Issued at 9:17am 24/10/2021
Valid from 1:00pm 25/10/2021 to 1:00am 26/10/2021
A weak front will move slowly eastwards over the central North Island during Monday with scattered rain or showers. During the afternoon and evening, there is a low risk of a few thunderstorms developing about inland areas from Waikato to the Whanganui hill country and across to central and southern Hawke's Bay as indicated on the chart. If any thunderstorms do develop, they will bring localised heavy rain. No other thunderstorms or significant convection expected over New Zealand on Labour Day (Monday).
Severe Thunderstorm Criteria
In New Zealand, MetService classifies a thunderstorm as severe if one or more of the following criteria are met:
Heavy rain (from thunderstorms):
Rainfall of 25mm/h, or more.
Large hail:
Hailstones 20mm in diameter, or larger.
Strong wind gusts (from thunderstorms):
Gusts of 110km/h (60 knots) or stronger.
Damaging tornadoes:
Fujita F1 - i.e. wind speeds greater than 116km/h (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.
