Flooding rain is likely in southeastern New South Wales, the ACT and eastern Victoria in the next few days, starting as early as today, which has prompted the issue of a flood watch. Over the next two-or-three days there is potential for 100 to 200 millimetres of rain, which is enough to cause significant flooding given recent rain in the area. For some this will be the heaviest rain they've seen since spring or last winter. The most likely area for this sort of rainfall is on the South Coast of NSW and in Victoris'a East Gippsland, but it is also possible over the Southern Tablelands of NSW, the ACT and the North East of Victoria. By early next week most of these districts will have exceeded their monthly average rainfall and also their summer average. The heaviest rain should stay away from Melbourne and Sydney but both cities can still expect an increase in showers late Friday and early Saturday with possible heavy thunderstorms. A low pressure trough is intensifying over the region with help from a pool of cold air moving in from South Australia. This trough will combine a feed of moist air from the Tasman Sea, courtesy of easterly winds. The trough was already active yesterday, triggering severe thunderstorms in central-western NSW. Dubbo gained 65mm in just over an hour, which is more than the monthly average and its heaviest rain in two years. The heaviest rain and storms are likely to fall on Friday when the trough is at its most intense. Once the pool of cold air moves off the east coast on Saturday, rain will generally ease. However, this pool of cold air will help a low pressure system form just offshore, which will generate strong winds and further heavy rain over the South Coast before the low moves away on Sunday, allowing wind and rain to ease.