The downpour across the east coast is forecast to intensify from today, with a warning of thunderstorms and high winds in many parts.

The Bureau of Meteorology is forecasting rainfall to increase across the central and northern coast from today, with moderate to heavy 24-hour rainfall totals of 40mm to 90mm likely and isolated falls exceeding 120mm possible.

In the north-west of the state, rainfall totals of 20mm to 50mm are forecast, with isolated falls exceeding 80mm possible.

Sydney is heading for a maximum rainfall of 35mm today, with a maximum of 45mm forecast for tomorrow.

Wind strengths will also increase over the coming hours. The bureau has issued a strong wind warning for the Macquarie and Hunter coasts from tomorrow.

Meanwhile, the drenching over south-eastern Queensland is forecast to continue for the next two days.

A trough moving east across the southern interior of the state is pushing into south-eastern parts, bringing the chance of thunderstorms near the coast, Wide Bay and Burnett and over the southern interior.

Brisbane is forecast to receive a maximum rainfall of 35mm today and tomorrow.

Warning of NSW flooding

Earlier this week, the SES warned of moderate flooding for coastal catchments in parts of the Mid North Coast, Northern Rivers and North West Slopes.

The ground is too saturated to absorb the rain in most affected areas, with much of eastern NSW having already had three to four times its average August rainfall this month.

The downpour is set to ease on Friday, with the system pulling back toward the coast.