Thunderstorm Outlook
Issued at 7:07am 17/05/2024
Valid from 7:07am 17/05/2024 to Midnight 17/05/2024
A front preceded by a strong moist northwesterly flow moves slowly north onto the far south of the South Island this evening. There is general low risk of thunderstorms over Fiordland from evening, but the risk is expected to increase to moderate about central Fiordland at night. Any thunderstorms that develop will boost local rainfall rates to 10-20mm/h. No other thunderstorms or significant convection expected over New Zealand during this period.
Issued at 8:58am 17/05/2024
Valid from Midnight 17/05/2024 to Midday 18/05/2024
A front preceded by a moist northwesterly flow moves slowly north over the north of Fiordland and the south of Westland Saturday morning. There is a moderate risk of thunderstorms for the north of Fiordland and Westland south of the Glaciers. These storms may be accompanied by heavy rain, 10 to 20 mm/h. There is a low risk of thunderstorms extending slightly farther inland and also farther north in Westland as indicated on the chart. No other thunderstorms or significant convection expected over New Zealand during this period.
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.
