A low will deepen off the NSW coast tonight, causing strong winds, heavy rain and large seas to batter the southern NSW coast. This low pressure system is bringing rain and thunderstorms to NSW today. As the low moves over the Tasman tonight and deepens, it will bring gale to storm force winds to parts of the NSW coast tonight and Sunday morning. The coast stretching from the Hunter to the South coast will bare the brunt of the winds, with southwesterly winds expected to reach 60-80km/h. On the South Coast, winds may even reach 90km/h at times. Widespread rainfalls of 10-20mm are also expected, with up to 50mm possible on the South Coast. The winds have prompted a storm force wind warning between Ulladulla and Merimbula, with a Gale Warning extending as far north as Smoky Cape and as far south as Gabo Island. The highest winds will be felt between 10pm tonight and 10am Sunday, with the strongest gusts expected between midnight and 5am. Further inland, conditions will be much calmer, with locations as far as just 15km inland likely to experience much lighter winds. As the low moves over the Tasman and deepens further, large waves and big swells will also increase. Seas should reach 4-5 metres between the Hunter and Illawarra coasts on Sunday morning, and should get as large as 6 metres on the South Coast. Swells should increase during the evening to around 4 metres. As the low speeds off towards New Zealand, winds and seas will ease, although swells should remain high until at least Monday. The calmer weather does not look it will last however, as another low looks set to develop later in the week.