The fire spread prediction map for January 4 represents the worst-case scenario for forecast conditions, RFS spokesman Brad Collins says.
The map is created using the forecast weather conditions and calculates the rate of fire spread based on that forecast.
The red zones are where the fire would spread to under those conditions if the RFS did nothing to attack the fire-front, however, other surrounding areas may come under threat if conditions change, or if fires breach containment lines.
The dotted red areas will most likely face ember attacks, rather than a direct fire-front.
Fire Spread Prediction for Sat 4 Jan 2020— NSW RFS (@NSWRFS) January 3, 2020
Dangerous fires in Shoalhaven, South Coast, Snowy Mountains & areas surrounding Greater Sydney. You should not be in potential spread areas or potential ember attack areas on Saturday. #nswrfs#nswfirespic.twitter.com/Ry14FXgPR2
"The ember attacks we can't do anything to reduce," Mr Collins said.
"But the potential spread is what would happen if we stood back and did nothing."
The RFS have been actively preparing to fight the blaze, but has warned people should not be in areas forecast to be affected by fire spread or ember attack tomorrow if at all possible.
"There may potentially be new fires burning in these areas that we do not yet know about, which may threaten you without warning," a statement read.
"Potential spread area - you should not be in this area on Saturday. Move to a large town outside this area, or if you are on the South Coast, move to an area that has already been burnt or go to the beach. Stay away from bush fire prone areas.
"Potential ember attack - You should not be in this area on Saturday as new fires could start and spread quickly."