"This rain won't calm the hot spots - it requires people to do work on them," Nettleton said.
A number of fires were started by lightning strikes yesterday as thunderstorms rolled over the area, including in Gawler near the main fire.
Areas as far apart as Border Town in the east and Streaky Bay on the Eyre Peninsula in the west are under threat from the storms.
Another fire was started yesterday near the incident command centre at One Tree Hill, believed to have been caused by a lightning strike.
Still, authorities believe they will have the fire fully contained within two days. The number of homes badly damaged or destroyed was also downgraded to 32 from 38.
An out-of-control bushfire threatening rural homes in Victoria's west has slowed down. An emergency warning for Glenisla Crossing and Cherrypool has been downgraded to a watch and act alert.
The fire started in the Black Ranges State Park in Victoria's west and broke through a containment line on its southern flank yesterday.
Updated advice from the Country Fire Authority said the fire was still travelling toward the communities, but its progress had slowed.
"Staying close to shelter is the safest option, in case conditions change again suddenly," the alert said.
Earlier, State Incident Control Centre spokesman Darren McKenzie said the conditions made the fire's path difficult to predict.
The weather bureau says Victoria and SA can expect rain today and tomorrow, with the chance of heavier falls through the weekend.AAP