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Remarkable swell event in NSW

Ben Domensino, Thursday July 16, 2020 - 12:58 AEST


Huge waves have been battering the NSW coast during the last three days as a deep low pressure system whipped up the Tasman Sea.


Large and dangerous waves started to develop along the NSW coast on Monday as a low pressure system took shape near the state's central coast. Since then, the deepening Tasman Low has caused very large and persistent waves along the state's coastline, hammering beaches and swallowing rock shelves.





Image: A huge wave breaks at Newcastle, NSW on Wednesday morning. Source: Finding Awe Photography / Facebook


A waverider buoy located roughly 10km off Sydney's Northern Beaches, registered maximum wave heights of more than 10 metres on Tuesday and Wednesday and up to nine metres on Thursday. The biggest wave recorded during this event was 11.58 metres early on Wednesday morning.


The Sydney waverider buoy has also been registering significant wave heights above four metres, continuously, since 9am on Tuesday. The term 'significant wave height' refers to the average height, from crest to trough, of the highest one-third of waves at a given location. This is a useful metric to get a good idea of the overall size of a storm wave event, with maximum wave heights prone to being exacerbated by individual 'rogue' waves.


Sydney's average significant wave high during July is 1.65 metres. This week, it climbed as high as 6.90 metres early on Wednesday morning. According to data collected by Manly Hydraulics between 1992 and 2016, the highest significant wave height during July was 6.96 metres and the probability of exceeding 6.5 metres near Sydney at this time of year is roughly 0.05%.





Image: Observed hourly wave heights off the coast of Sydney, with data highlighted at 3am AEST on Wednesday. Source: Manly Hydraulics Laboratory.


Elsewhere, significant wave heights reached up to 6.12 metres at Coffs Harbour and 5.94 metres at Eden in NSW, and over four metres near North Stradbroke Island in Queensland, earlier this week.


Waves will gradually ease along Australia's east coast during the next few days, although conditions will remain dangerous late into the week. A hazardous surf warning is in place between southern NSW and southeast Queensland for Thursday and Friday.


- Weatherzone

© Weatherzone 2020

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