Large and powerful ocean swells are thundering onto the shores of southeast Queensland today, as Ex-Tropical Cyclone Fina sends the Coral Sea into overdrive. While Fina did lose its tropical cyclone status two days ago, it has actually become a more potent system for swell generation in the last 12-24 hours. Fina has under gone a secondary intensification in its transition to a mid-latitude low pressure system in the last 24 hours, setting up a broad region of easterly gales as it presses up against a large high pressure system to the south. The gale-force easterly winds between these two large weather systems are sending a stream of ever growing swell onto the Queensland coast, with the Sunshine and Gold Coasts both experiencing a notable swell increase today. Average wave heights on the Sunshine Coat have been measured at 2.5 metres through Saturday, with maximum wave heights in the 4-5 metre range. The Gold Coast wave buoy has been recording average wave heights of 2 metres and maximum wave heights in the 3-4 metre range. With Ex-TC Fina maintain a broad band of easterly gales off the southeast coast of Queensland through the remainder of Saturday and early Sunday morning, the surf is only going to get bigger and more powerful. The swell should continue to build through Christmas Day, with a peak in size most likely during the afternoon hours. Wave heights in the surf zone at east facing beaches have the potential to reach 12-15ft, or 4-5 metres in metric terms. Offshore, maximum wave heights of over 6 metres are likely. It goes without saying that swells of this size are treacherous for all marine activities. It will even be a challenging day for the most experienced surfers who will no doubt attempt to tackle these monstrous waves. Beach erosion is also going to be a significant factor on Christmas morning along exposed parts of the southeast Queensland coast, with a large astronomical high tide occurring just before 9am. The added effects of strong winds blowing onto the coast and lower than usual air pressure will all boost the high tide mark well above the predicted astronomical value. The increased wave action on top of this abnormally high tide will be a major factor in creating erosion of beaches and dune systems. The large surf will persist for southeast Queensland on Boxing Day, so extremely hazardous conditions will remain for holiday makers planning a day at the beach. Even boating would not be sensible on a day like this. Swell conditions will only slowly abate in Queensland during the week. It's also worth noting that this swell knows no borders, with large and dangerous waves spreading down the New South Wales coast during Christmas Day and Boxing Day. The northern half of the NSW coast will see the brunt of the swell but even Sydney beaches can expect large and dangerous waves of over 6 feet (2 metres) on Boxing Day. There can be breaks of 10-20 minutes between the arrival of the largest 'set' waves, so this can catch rock fisherman and swimmers offguard. Given the forecast of warmer weather in Sydney on this day, it shapes as a treacherous day for the city's beaches and in fact the entire NSW coast.