Parts of Sydney, the Illawarra, Central Tablelands, Central West Slopes and Plains and Hunter are all at risk of being struck by a severe thunderstorm for the second day running after being hit yesterday. Today's thunderstorms should peak in intensity and number during the afternoon when they bring the greatest risk of generating heavy downpours, damaging winds and hail. Among the most likely areas is western Sydney where any storm has potential to bring 20-to-30 millimetres of rain in quick time, wind gusts greater than 90 km/h and hail. A low pressure trough causing these storms has been slow-moving and large in area, giving many places a storm for at least two days running. Its slow-moving nature allows skies to clear each night and morning, providing sunny and humid warmth for storms to develop again the next afternoon. This also gives time for residents to tidy up and prepare for the next round. This trough will continue to move east, taking the most intense storms offshore and to the north of New South Wales tonight. On Sunday some places have a chance to see a storm for the third day running, most likely north of Sydney. The Hunter, Mid North Coast, Northern Rivers, Northern Tablelands and North West Slopes and Plains are most at risk of experiencing flash flooding, damaging winds and hail.