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Severe thunderstorms

Severe thunderstorms are the most common type of storm in NSW. Thunderstorms can range in size from a few hundred metres to around ten kilometres in diameter.

A severe thunderstorm ‘supercell’ can cause extensive damage.

Thunderstorms can include:

  • Very strong winds (at least 90 km/h and sometimes greater than 200 km/h)
  • Large hail (at least 2cm in diameter)
  • Very heavy rain (leading to flash flooding)

Severe thunderstorms can cause:

  • Severe damage to buildings, especially roofs, skylights and windows.
  • Whole buildings to be damaged or demolished as a result of fallen trees.
  • Damage to cars parked on streets
  • Downed trees and power lines
  • Extended periods of electricity, connectivity and telephone outages.

Ask the Bureau: What is a severe thunderstorm?

Tornadoes 

A tornado, also known as a twister is an intense, funnel-shaped column of rotating air, that extends from the storm clouds to the ground during severe thunderstorms over areas of land. Tornadoes can range in size from a few metres to around one kilometre in diameter. They have extreme winds which can range from 120 km/h to above 400 km/h, with an intense updraught capable of lifting heavy objects such as cars and trees and causing extensive damage.

Tropical cyclones and ex-tropical cyclones

Cyclones, called hurricanes or typhoons in other parts of the world, can sometimes affect New South Wales, with the coastal areas in northern parts of the state being most at risk. Although, the impacts of cyclones can extend to the south and inland areas of NSW.

Cyclones form over warm tropical waters where the sea's surface temperature is above 26° C. A cyclone forms in an area of low pressure, which draws in surrounding winds. As the Earth rotates, it creates forces that cause the winds to swirl around the low pressure. This helps the cyclone start to spin. They are typically hundreds of kilometres in diameter and can last for many days, bringing strong winds, heavy rain, flooding and storm surges that can cause major damage.

East Coast Lows and Low-Pressure Troughs

Intense low-pressure systems known as East Coast Lows and Low-Pressure Troughs are more common in NSW. They generally develop close to the coast and can intensify dramatically. They can produce gale to storm-force winds, heavy rainfall, and in some cases very high seas and storm surges.

Due to their relative fast development and short life cycle, warnings issued for East Coast Lows will usually have less lead time. The Bureau of Meteorology forecasts may also mention localised heavy rainfall, strong winds and dangerous surf, in the lead-up to an East Coast Low or Low-Pressure Trough.

Ask the Bureau: What is an East Coast Low?

Cold fronts, southerly busters, cold outbreaks and snow storms

Cold fronts 

Cold fronts produce strong winds and rainfall. Gale force westerly winds associated with Cold Fronts can occur across wide areas of NSW particularly in the winter months.

Ask the Bureau: What is a cold front?

Southerly busters

Southerly busters produce wind changes that mostly affect coastal locations east of the Great Dividing Range and are common during the warmer months. Winds following a southerly buster can be strong and gusty for several hours with peak wind gusts of around 90-100 km/h.

Cold outbreaks

Cold outbreaks can form from late autumn to early spring, where cold air advances northwards over NSW resulting in unseasonably cold temperatures and in some areas, snowfalls and snow storms. These conditions produce snow and ice-related problems on roads. Vehicles can be stranded on roads, and communities can be isolated. Communication and power can also be disrupted.