SW Maritime assistant executive director Alex Barrell said conditions are expected to deteriorate from Monday due to an east coast low pressure system forming off the coast.

"Between 150 and 300 millimeters of rainfall may fall in some areas between Monday and Wednesday accompanied by strong gale force winds," Mr Barrell said.

"The seas are likely to be very rough and localised flash flooding is expected which may impact the South Coast and will be more severe if the trough moves north to the Central Coast.

"Although it is winter and there are fewer boaters on our waterways, it is school holidays and skippers need to remain vigilant if children are on board.

Read more: Heavy rains due to hit the Illawarra and South Coast

"Everyone should wear a lifejacket at all times and, if bad weather impacts your trip, skippers should find a well-protected waterway as a Plan B, or not head out on the water at all.

"Skippers and owners of small boats should be on high alert and check the conditions before considering crossing a coastal bar or heading offshore.

"While conditions are expected to ease by Wednesday, large ocean swells are likely to persist for some days and crossing ocean bars will remain a challenge for navigation."

"NSW Maritime strongly recommends reconsidering your need to be out on the water in those affected areas over the next few days."

Skippers are reminded they are responsible for the safety of their vessel and everyone on board.

NSW Maritime and Centre for Maritime Safety have offered the following safety tips;

Further information at www.rms.nsw.gov.au/maritime

Offshore boating safety: www.maritime.nsw.gov.au/campaigns/offshore.html

Lifejackets: www.lifejacketwearit.com.au

Live vision of bar crossings: www.maritime.nsw.gov.au/webcams/web-cam.html

Official forecast: http://www.bom.gov.au/marine/index.shtml#nsw

Boating safety images: www.flickr.com/photos/nswmaritime/

Meanwhile the NSW SES is urging residents across the Illawarra and South Coast to prepare for possible severe weather.

The Bureau of Meteorology has forecast heavy rainfall along the coast between Kiama and Merimbula on Monday, followed by strong winds on Tuesday, with conditions expected to ease later in the week.

NSW SES Incident Controller for South Eastern Zone, Tom Jory urged residents to prepare ahead of the change in weather conditions.

"Strong winds are common for this time of year. History has shown those who take steps to prepare are less likely to be impacted."

"There is still time to take some simple steps to prepare your property. Clear gutters and drains, trim tree branches and secure outdoor furniture, including trampolines.

Parts of the South Coast recently impacted by bushfires are at increased risk.

"Strong winds pose a greater risk of fallen trees in areas affected by the fires. Flash flooding is also possible - which is worsened by the lack of vegetation."

Mr Jory encouraged residents to keep aware of surroundings and avoid unnecessary travel through bushfire-affected areas during strong winds.

The NSW SES recommends people monitor the NSW Bureau of Meteorology for any severe weather warnings for heavy rain or severe wind warnings.

NSW SES volunteers are on standby to assist communities and additional resources will be available to assist areas.

For more advice on how to prepare for storms and floods, visit the SES Get Ready website www.ses.nsw.gov.au/getready. For emergency storm and flood assistance, call NSW SES on 132 500.

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