Overnight, southerly winds strengthened through the Harbour City reaching as high as 115km/h at Wattamolla in the Royal National Park. Further north, winds reached 80km/h at the Harbour and 93km/h at Little Bay. Winds were strongest along the coastal fringe with the eastern suburbs, the northern beaches and Cronulla seeing 70-80km/h wind gusts. Away from the coast, western suburbs were also windy but managed to escape the brunt of this system. Penrith register 52km/h winds late this morning with Terrey Hills seeing maximum winds of up to 59km/h and 61km/h at Bankstown. The reason for these winds is an East Coast Low (ECL) which developed throughout the night over the Tasman Sea on the southern flank of a cold front that swept the city earlier yesterday. Southeastern Queensland, New South Wales and eastern Victoria are susceptible to this kind of weather phenomena throughout the year, most commonly in late autumn and early winter. ECLs can cause significant damage along the eastern states due to heavy rainfall, damaging winds and powerful surf. One good example is the grounding of the M. V. Pasha Bulker in 2007 in Newcastle, an event that lead to nine deaths and about $1.6 billion in insurance claims. Earlier this morning, waves of up to 11 metres were registered off the Harbour with waves of about four to six metres breaking along the exposed beaches. Moreover, the powerful surf has generated a storm surge of about 20 centimetres enhancing some coastal erosion along the city beaches. However, every dark cloud has a silver lining and ECLs have profound effects on the water supply along the east coast contributing significantly to the annual regional rainfall. Most of the region's stored water supply derives from the high intensity rainfall from ECL with some events intense enough to double the dam levels. This is now the third major ECL to develop in the past three weeks making a perfect trifecta. Compared to the other two, however, this is not looking to bring much rainfall with just 5mm recorded at Observatory Hill on the 24 hour period to 9am this morning. The highest totals being 10mm at Bondi and Randwick. The ECL will maintain strong and gusty southerly winds across the city throughout the day, strongest along the coastal fringe. Winds will then gradually ease overnight with showers becoming less frequent. Tomorrow will continue to be windy, but not to today's extend with Friday finally seeing stable conditions returning. Across the beaches however, the dangerous surf is expected to peak later today and tomorrow morning and won't begin to ease until Friday with SLSA advising against all coastal activities until Saturday 6th September.