Heavy rainfall is forecast for the south coast on Tuesday, with small hail also possible. 'Mid-May is a very unusual time of year to see severe storms in NSW,' forecaster Jake Phillips said. 'In this particular case it's due to the combination of having a relatively significant amount of humidity around for this time of year, and also a very powerful upper level system moving through,' The storm activity will likely begin early in the morning, before peaking in the afternoon and petering out over Wednesday and Thursday. Sydney and the Hunter region should be spared, but the BOM is urging all residents along the coast to be prepared for severe storms.