Sydney's temperature is forecast to climb into the 30s for the first time this spring on Saturday before a strong cold front sweeps in, triggering a "drastic drop" in temperatures.

The Bureau of Meteorology has issued a severe weather warning for "vigorous" and damaging winds on Saturday for the area stretching from Wollongong south almost to the Victorian border.

The gusty conditions along with dry conditions prompted the NSW Rural Fire Service to raise the fire danger threat level for the Sydney Metropolitan region to "severe" for Saturday, triggering a total fire ban.

Other areas with total fire bans include Hunter, the Illawarra and the state's northwest, all of which will also have "severe" fire danger ratings.