Black nor'easter facts for kids

The dark storm clouds associated with the Black nor'easter over Sydney CBD

A black nor'easter is a powerful storm that happens on the east coast of Australia. It usually brings strong winds and heavy rain. These storms mostly affect areas from southeastern Queensland down to southern New South Wales. They typically occur between late spring and early autumn.

This type of storm starts offshore as a deep area of low pressure. You can tell one is coming when thick, dark clouds quickly build up. These clouds bring a lot of rain and strong winds from the northeast. A black nor'easter can be a mix of different weather systems. It can include surface troughs, winds blowing from the ocean, and a low-pressure area. These storms can even make warm days feel cooler because of the thick, moisture-filled clouds.

Black nor'easters were first written about in the 1800s. They got their name because the very dark clouds can make the daytime as dark as twilight.

How They Form

Dark clouds forming before the storm in Darling Harbour

A black nor'easter forms when moist, cooler air from the south mixes with warm, humid air from the north. The northeast winds gather this moisture, creating dark, rain-filled clouds. The first time a black nor'easter was described was in the Sydney Morning Herald on October 30, 1911. It talked about a storm in southern New South Wales.

Northeasterly sea breezes are common along the New South Wales coast in summer. They happen because of temperature differences between the sea and the land. But a black nor'easter is much stronger. It is caused by bigger weather patterns that make these onshore winds much more intense. It's called "black" because of its very dark grey, almost black clouds. It also brings strong, moist winds, often around 60 kilometers per hour. These winds are pushed by strong high-pressure systems. The storm can then bring thunderstorms, heavy rain, and sometimes hail.

Black nor'easters are different from an East coast low (ECL). ECLs usually happen in cooler months, while black nor'easters happen in warmer months. Black nor'easters also start from the northeast. However, a black nor'easter can sometimes turn into an east coast low as it moves south. This happened during the 2022 eastern Australia floods. Unlike ECLs, black nor'easters can also heavily affect areas further inland in New South Wales and Queensland.

What Happens During a Storm

The virtually black clouds associated with the storm over Darlinghurst

Black nor'easters are often cut-off low systems. These systems interact with coastal troughs that are full of moisture. This pulls in humid, tropical air from the north. The cold air high up in the sky then cools down the warmer, wet air. This forces a lot of moisture to fall as rain. This combination often leads to heavy rainfall and flooding on the east coast. Warm sea temperatures from the East Australian Current (EAC) can make black nor'easters even stronger.

Forecaster Craig Brokensha described a black nor'easter as "an unstable low-pressure trough moving from inland Australia, with moisture feeding into another trough sitting near the East Coast, and the two are predicted to combine." They can also form when a cool pool of air arrives from the Great Australian Bight. This can create a low-pressure system over the southeast at the same time as a moist coastal trough. The warm sea temperatures fuel this trough. This can cause more evaporation, adding more water to the air. When this moisture is brought south by moist northeasterly winds and chilled by cooler air higher up, it turns into rain.

These storms often cause a big increase in wave heights along the east coast. They create strong northeast air currents and powerful storm waves over the western Tasman Sea. The winds often produce large waves. When a black nor'easter combines with an east coast low, it can create the most intense storm waves.

Impacts of Black Nor'easters

Black nor'easters can cause a lot of damage. The strong winds can make trees fall, which has unfortunately led to deaths in New South Wales, especially in Sydney. These storms also bring very heavy floods. They can knock down power lines, leaving thousands of homes and businesses without electricity. Sometimes, roofs can even collapse.

Major Storms

• In February 2010, Sydney had some of its heaviest rain in 25 years. This came with strong thunderstorms and gusty winds. The storms cut power and damaged homes.
• On November 18, 2013, a tornado hit Hornsby, a suburb in Sydney. The tornado was 2 kilometers long and 50 meters wide. It blew off roofs and knocked down large trees. Winds in the tornado reached 140 kilometers per hour. Twelve people were injured.
• The black nor'easter swell in June 2016 changed parts of the east Australian coastline. Backyards fell into the sea at Collaroy, and nearby houses were damaged. Bridges, piers, and walkways were also destroyed. Almost every north-facing beach had some erosion. In Cronulla, large boulders were thrown from under the water onto a rock platform.
• Between February 7 and 9, 2020, the Sydney area received its heaviest rain in 30 years. There was widespread flooding and strong winds. This caused problems for commuters and left over 100,000 homes without power. Sydney CBD recorded about 391.6 millimeters of rain in those three days. The storm also affected the South Coast, Blue Mountains, Southern Highlands, Hunter Valley and the Central Coast.

Black nor'easter clouds over southeast Australia (March 2021)

• On March 20, 2021, a tornado damaged homes and knocked down trees in Chester Hill, a western suburb of Sydney. Thousands were left without electricity. The storm also brought record rainfall to the north coast. Towns near Port Macquarie, like Kendall, saw over 400 millimeters of rain between March 19 and 20.
• In late February and early March 2022, a black nor'easter lasted for almost two weeks. It caused severe flooding in major cities like Brisbane, Lismore, and western Sydney. This nor'easter turned into an east coast low as it moved south.
• The July 2022 floods were caused by a black nor'easter. Tropical moisture from northern Australia mixed with a low-pressure trough on the New South Wales coast. This later became an east coast low.
• Between April 4 and 6, 2024, a black nor'easter brought heavy rain to southern Queensland and New South Wales. It caused the deaths of two men, one in Logan, Queensland and one in Western Sydney. Penrith recorded its heaviest rainfall ever, with 167 millimeters. Over 100 millimeters fell in parts of southern Queensland and the NSW Northern Rivers on April 4, causing floods.

See also

• Southerly buster
• Australian east coast low
• Severe weather events in Sydney