In a Facebook post, the Southern Tablelands zone stated that the area was witnessing the early stages of deteriorating conditions across the Southern Ranges.

"The forecast conditions expected to influence the Currowan Fire over the next 48 hours will make it more erratic and unable to be controlled despite the best efforts of our firefighters," it stated.

"We strongly urge these communities to pre-emptively enact their Bushfire Survival Plan.

"Under the forecast conditions, your best chance of survival is to leave and leave early.

The establishment of tactical plant work with the use of heavy machinery will continue behind properties in the area in an effort to slow the path of the fire and offer some property protection, but again we have to stress that under these conditions, containment strategies are unlikely to hold.

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"Please stay up to date by downloading the Fires Near Me App on your phone, going to the NSW Rural Fire Service Website, contacting the Bushfire Information Line 1800 679 737 and the ABC is the Emergency Broadcaster."

The notification comes after the RFS hosted weekend meetings in each community to warn of the Currowan Fire's potential impact. Operations director Lachlan Gilchrist said traditional containment strategies would not work, given the fire's erratic behaviour.

The advice also follows a Bureau of Meteorology weather warning predicting winds averaging 60 to 70 km/h with peak gusts in excess of 90 km/h. These are possible for the Snowy Mountains, and parts of the Australian Capital Territory, South Coast, Southern Slopes and Southern Highlands from late Monday night or early Tuesday morning. Higher ground and exposed areas are most susceptible.

Southern Tablelands operations director Lachlan Gilchrist said the wind was picking up in the Nerriga area.

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"It's a very small slither so it's difficult to say whether it will be a significant factor (further south)," he said.

The Charley's Forest fire, which has currently burnt 34,156 hectares, was upgraded to emergency status at 4.30pm Monday and residents in the areas of Oallen Road, Nerriga Road and Charleys Forest Road were advised it was too late to leave.

Mr Gilchrist said the RFS wasn't expecting the Bureau's latest forecast.

"It's just an unstable air mass and that in itself is concerning," he said.

He said Tuesday was going to be a difficult day.