The city can expect 30-45 millimetres of rain on Thursday, with the chance of a thunderstorm in the morning and afternoon, the Bureau of Meteorology said.

Temperatures will sit in a narrow range of 23-26 degrees for the whole day.

The bureau issued a severe weather warning on Wednesday for heavy rainfall and damaging winds for the coastal fringe of NSW from Sydney north to the Queensland border (see chart below).

"A low pressure system over central-eastern Queensland and a high pressure system over the Tasman Sea are dragging a humid tropical air mass over parts of NSW," the bureau said.

"Heavy rainfall over north-eastern NSW is likely during Thursday and Friday as a cold front approaches from the south-west and interacts with this humid air mass."

Showers should return on Friday with temperatures becoming notably cooler for the next week.

The heaviest falls in NSW on Thursday are likely to be in the state's north-east corner from about Coffs Harbour north.

"Twenty-four hour totals in excess of 100 millimetres are expected over the Northern Rivers district during Thursday, and it is likely that some locations will exceed more than 250 millimetres," the bureau said.

Sydney's rainfall is likely to push the March total above 300 millimetres, or more than twice the norm for the month. It is already the city's wettest March since 1984.

The warning of coming rough weather for Sydney is more from the wind than rain, the bureau said.

"Damaging winds averaging 65km/h with gusts in excess of 90km/h are possible along the coastal fringe, from about Sydney to Forster during Thursday afternoon and evening, then extending to the remainder of the northern coastal fringe during Friday.," the bureau said.

Dangerous surf conditions are also likely on Thursday and Friday.

The bureau has issued a separate warning of gale force winds for Sydney's closed waters and the coast, the Hunter, Illawarra and Batemans coasts for Thursday.

Saturday is likely to be generally dry but the arrival of another cold front on Sunday should see showers redevelop "with the odd heavy falls on the coast", said Brett Dutschke, a senior meteorologist with Weatherzone.

Record winds

The slow-moving nature of Cyclone Debbie and its remnant low brought sustained intense winds and heavy rainfall to parts of Queensland.

Totals of more than a metre of rain have been recorded in the hinterland ranges near Mackay over a 48-hour period, Mr Dutschke said.

Clark Range alone collected 646 millimetres in the 24 hours to 9am Wednesday and Mount William 568 millimetres. By contrast, those regions would normally expect about 1500-2000 millimetres of rain over a year.

The bureau confirmed Debbie's winds were the highest recorded at its stations in Queensland - smashing the previous record by 56km/h. The maximum gusts fell just shy of the most recorded in Australia, the 267km/h reading set at Learmonth Airport in March 1999. (See bureau data below).

Cyclone Yasi in 2011 had an estimated wind speed of 285km/h in Queensland, based on pressure readings but that value was not registered on any of the bureau's sites.

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