Heavy rain and flooding are occurring along the East Coast of the U.S., primarily from South Carolina to the Mid-Atlantic States; this deluge, expected to persist for the next two days, is triggered by three atmospheric factors.
First of all, the leading edge of an atmospheric trough lies along the East Coast; cool, dry air behind this stationary front knifes beneath the warm, moist air ahead of the trough, producing lift. Secondly, a dome of high pressure sits over the North Atlantic, east of Nova Scotia; clockwise winds swirl around this high, sweeping Atlantic moisture toward the East Coast. Finally, as Hurricane Joaquin moves NNE, paralleling the coast, its counterclockwise winds will augment the onshore flow.
These three factors are expected to produce copious rainfall throughout the Carolinas, perhaps totaling more than eighteen inches in some areas; significant but lesser amounts of rain are forecast for the Mid-Atlantic region to southern New England. Heavy rains in the mountains (most likely to occur in northern South Carolina) may be especially destructive, unleashing mudslides and valley floods. In addition to the torrential rain, wind driven waves are expected to cause beach erosion and coastal flooding throughout the region.
