The Bureau of Meteorology has issued a warning about potentially widespread thunderstorms affecting large parts of New South Wales today.

Many areas are bracing for more heavy rain and possible flash flooding as a large cloud system moves across the country. A low-pressure system combined with a cold front is expected to push this weather system from South Australia toward the east coast throughout today and tomorrow.

Some regions, including the southern Illawarra, the northern parts of the South Coast, and the eastern Southern Tablelands, could see between 60mm and 100mm of rain within just six hours starting this evening. Coastal areas may even receive as much as 140mm in 24 hours.

The Bureau posted on social media platform X that these storms could be widespread and potentially severe, bringing heavy rain, strong winds, and large hail. If those conditions develop, thunderstorm warnings will be issued. People are being urged to stay informed throughout the day.

Severe weather warnings are currently in effect for Lord Howe Island, the Illawarra, parts of the South Coast, and the Southern Tablelands. At this stage, only one minor flood warning has been issued, which is for the Namoi River.

Sydney is expected to get between 15mm and 45mm of rain today, with the heaviest falls easing off by the evening.

Senior meteorologist Miriam Bradbury said strong wind gusts and large waves are likely along coastal areas as the system lingers offshore, pulling in moisture and strong winds that could lead to more severe weather between the Hunter region and the South Coast.

Rain and storms will also pick up across northern Victoria and southern Queensland over the next two days as the system moves east and becomes more intense.

According to meteorologist Jonathan How, eastern and southeastern NSW, along with northeastern Victoria, could see moderate rainfall and more storms, with the risk of damaging winds and heavy downpours.

Wednesday is expected to bring cold, wet conditions to Sydney and Canberra, with showers also forecast for Melbourne and Adelaide.