Widespread rainfall across NSW is expected through the second half of the week, as a deep low pressure system interacts with very humid tropical air, the State Emergency Services bulletin issued Tuesday afternoon says.

Very intense rainfall rates are likely for some areas, most likely over the north from late Wednesday.

The heaviest rainfall is forecast to contract to the south east of the state through the weekend as the low moves offshore.

With catchments already relatively wet following earlier rainfall, the SES says the Lachlan River is likely to be affected.

As of Tuesday, Wyangala Dam was at 99.9 per cent of capacity according to the Water NSW website.

Downstream of Forbes, farmers have already seen minor and moderate flood levels wiping out this season's crops.

At this early stage they advise the Lachlan River to Cottons Weir just upstream of Forbes could see anything from minor to major flooding.

For now, we are being advised to monitor weather forecasts and warnings and be prepared for the possibility of flooding in impacted areas.

Farmers are encouraged to:

Flood Warnings will be issued if Minor Flood Level is expected to be exceeded at key sites along the main river for which the Bureau of Meteorology provides a flood warning service.

For emergency help in floods and storms, call the NSW State Emergency Service on 132 500. In life threatening situations call triple zero (000) immediately.

The next bulletin will be issued 1pm Wednesday and the Advocate will share the update.

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