Large and powerful surf conditions are expected to batter most of the NSW coast for most of the working week as a low-pressure system that delivered a weekend drenching continues to linger off the state's coast.

The Bureau of Meteorology issued a warning on Monday morning for large and powerful surf conditions from the South Coast to the North Coast for Monday and Tuesday at least, and the conditions are likely  to persist until Thursday.

The high seas - with waves expected to be three metres for much of the week - will make it hazardous for coastal activities such as rock fishing, swimming and surfing, the bureau warned.

Weatherzone senior meteorologist Jacob Cronje said the strong low-pressure system that delivered heavy rainfall across parts of NSW over the weekend continued to linger off the NSW coast.

"It's now more defined and well developed, even though it's offshore, so its effects are lingering," Mr Cronje said.

 "It's fairly slow moving as it's tracking to the north-east.

 "There is a very strong pressure gradient between the system and the coast, and there is also a good south-easterly circulation that's stretching over a very large area of ocean.

"When you have sustained south-easterly winds over a very large area of ocean making its way towards the coast, you usually have increased wave activity."

Mr Cronje said the big surf conditions were expected to remain in Sydney until Thursday at least, when the low-pressure system tracked further north.

The bureau is forecasting a mostly sunny day in Sydney on Monday with a high chance of showers along the coastal fringe.

A top of 25 degrees is forecast for the city and 28 degrees for the west.

A shower or two and maximum temperatures in the mid 20s are forecast each day for Sydney for the rest of the week.

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