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 7:22pm 17/05/2024
Valid from Midnight 17/05/2024 to Midday 18/05/2024
Updated at 7:20pm Friday - Minor changes only. A front preceded by a moist northwesterly flow moves slowly northwards over Fiordland and southern Westland during Saturday morning. There is a moderate risk of thunderstorms embedded within broader areas of rain for central and northern Fiordland, and southern Westland, during the morning. A low risk of thunderstorms affects southern Fiordland before dawn, and central Westland later in the morning. Any thunderstorms that develop will boost local rainfall rates to 10-25mm/h. No other thunderstorms or significant convection expected over New Zealand on Saturday morning.
Issued at 7:26pm 17/05/2024
Valid from Midday 18/05/2024 to Midnight 18/05/2024
Updated at 7:20pm Friday - Low risk added to Westland. A front and associated rain-band will move slowly northwards through Westland during the second half of Saturday. There is a low risk of a few thunderstorms associated with the front about central Westland during Saturday afternoon and evening. 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.
