An east coast low has been dumping heavy rain over the NSW coast with a supercell thunderstorm- the rarest and most intense type of storm- spawning a tornado that severely damaged 30 homes in Lennox Head yesterday morning. Supercell storms are not only rare in general, but they're even more rare in June which is two months after the official storm season. However yesterday's atmospheric conditions created the perfect set up for a supercell. We had warm humid air at the surface and very cold and dry air aloft- the contrast between the two air masses created a great amount of instability leading to the supercell formation. Supercells are characterised by a rotation in the cloud and when heavy rain bursts down to the surface, the downdraught can carry this rotation right down to the ground which materialises as a tornado. We normally get around 20 tornados in Australia every year but because they often occur in unpopulated areas they usually go unreported.
Apart from serious tornado damage, heavy rain is also drenching the NSW coast. As much as 171mm fell across Ballina in a 24 hour period to 9am yesterday morning, its heaviest rain in 6 years. The low has shifted further south today so rain has eased for the Northern Rivers, but increased across areas to the south of the low like the Mid North Coast and Hunter districts. To 9am this morning, Port Macquarie Golf Club picked up 83mm and Norah Head received 56mm. Heavy overnight rain also delivered over 50mm to Sydney's suburbs including North Rocks, West Pennant Hills and Hornsby. Heavy rain will continue between Port Macquarie and Wollongong today, easing back tomorrow as the low moves east. However, rain will intensify once again on Sunday.
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