The combination of the remains of Isaac and a stationary frontal system will continue to produce occasional heavy rain throughout the Mid-Atlantic region right through Wednesday. The Philly metro region has been especially hard hit over the last 18 hours or so with some areas already receiving up to 3 inches of rain. Deep and focused low-level moisture convergence along the frontal boundary zone has helped to generate numerous bands of heavy showers and embedded thunderstorms from SE PA across to South Jersey and southward to the Delmarva Peninsula. These bands have been moving northward all day from the Delmarva Peninsula region and they have been redeveloping to the south as the overall atmospheric instability remains in place. Some serious flash flooding has developed in parts of the region and, unfortunately, we’re a long way from being out of the woods as, while it won’t rain continuously, the heavy rain threat will continue through Wednesday. There may be a break in this wet pattern late this week, but then more rain is possible this weekend.