Low pressure systems off the New South Wales coast and associated hazardous weather: establishment of a database

The New South Wales (NSW) coast is subject to heavy rain, strong wind and large waves resulting from low pressure systems over the adjacent Tasman Sea that develop from a variety of synoptic and mesoscale mechanisms. A database of these maritime lows and their impacts has been developed in the NSW Climate Services Centre of the Bureau of Meteorology. The database currently extends back to 1970 and includes data on rainfall amounts, with wind speed and significant wave height data still to be added. The database events were classified into six synoptic types based on the mean sea level pressure synoptic pattern in which the lows formed. The six types are: inland trough lows (30 per cent), easterly trough lows (14 per cent), and ex-tropical cyclones (4 per cent), all of which originate in the subtropical or tropical easterlies; and, lows forming on a wave on a front (37 per cent) decaying front lows (12 per cent) and lows in the westerlies (3 per cent), the latter two of which originate from mid-latitude low pressure systems or fronts in the westerlies. Since 1970, only inland trough lows have shown a significant increase in frequency which is consistent with a slight increase in spring rainfall in an area over northeast NSW over the same period. In contrast, there has been a decrease in ex-tropical cyclone numbers impacting the NSW coast since 1970, which is consistent with a decrease in summer rainfall generally along the NSW coast. The development of the database is ongoing but it is planned to extend it back in time to further investigate the relationship between maritime low pressure development and NSW coastal rainfall trends.