A severe storm is expected to narrowly miss Canberra on Monday afternoon.

Sydneysiders look set for a soggy commute to end the working week, as an intense low pressure system off the coast delivers widespread showers, wind and large and powerful surf conditions to the city.

Unless you've been inside a 200kmh blast of wind it's hard to imagine the tremendous natural force behind it.

Growing winds and driving rain from Hurricane Hermine lashed Florida's northern Gulf Coast on Friday as forecasters warned of "life-threatening" floods.

The impacts of the monster El Nino in the Pacific are likely to intensify across much of Australia, including worsening drought and an elevated bushfire threat, after conditions that were nullifying its effects suddenly retreated.

Temperatures in Canberra reached 38.5 degrees as the region's first heatwave of the year peaked on Wednesday.

The trough that brought a series of storms to Canberra on Saturday is expected to affect the region until Monday.

Fires breached containment lines in two NSW locations on Sunday morning as temperatures climbed above 35 degrees in parts of the state and Sydney.

A fierce blast of winter has prompted a severe weather warning for most of southern NSW, including Sydney.

It will snow in the ACT tonight as a cold front moves over the region, the Bureau of Meteorology says.