Eastern Flood Threat Begins; Strong Winds, Coastal Impacts Also Possible

Chris Dolce
Published: September 29,2015
The forecast for the East Coast is looking increasingly ominous as a complex weather pattern promises to deliver more heavy rainfall to a region that is already dealing with flooding from recent deluges.
(MORE: Serious Flooding Inundates Virginia)
An initial round of heavy rain will continue to drench much of the Northeast through Wednesday as moisture-rich air from the Gulf of Mexico is wrung out by a slow-moving cold front. This rainfall has already brought major flooding to parts of Virginia.
Late in the week and this weekend, moisture from Tropical Storm Joaquin in the western Atlantic will be involved in this soaking setup as the front stalls near the East Coast. That said, significant impacts are likely in portions of the East no matter how much Joaquin is involved due to the large-scale weather pattern taking shape. This will include, flash flooding, river flooding, gusty winds, high surf, beach erosion and some coastal flooding at high tide.
(MORE: Latest on Tropical Storm Joaquin)
Below we look at the forecast details on what we can expect in the week ahead.

Through Wednesday: Cold Front Provides Soaking

Current Radar, Flood Alerts

Rainfall Forecast Through Wednesday Evening

The first component to this soaking setup is a cold front that will slice through the eastern states into Wednesday while intercepting moisture from the Gulf of Mexico and the Atlantic.
Another ingredient is an upper-atmospheric low pressure center that has been stalled near the Texas Gulf Coast since this past weekend, and has contributed to heavy rain and flooding in the northern Gulf Coast states. That upper low will weaken and get pulled north and east by the front, helping to add extra lift in the atmosphere needed for the generation of widespread clouds and rain.
Through Tuesday night, locally heavy rain and pockets of flash flooding will continue in a broad swath ahead of the cold front from the southern Appalachians into the interior Northeast.
The National Weather Service has issued flood watches from western North Carolina's Smoky Mountains to Maine.
(MAPS: Interactive Radar | Flood Alerts)
Tuesday night into Wednesday, the cold front will move to near the Northeast coast where it will begin to stall, bringing the threat of locally heavy rain closer to the I-95 corridor of the Northeast. Once again, flash flooding will be a concern.
(FORECAST: Harrisburg, Pennsylvania | Albany, New York | New York City | Boston)
Our forecast rainfall map shows that parts of the interior Northeast and New England may see 3 inches or more of rain through Wednesday.
However, the threat of heavy rain doesn't end there, and we may see additional impacts along the coast late this week into the weekend.

Late Week-Weekend: More Heavy Rain; Wind, Coastal Impacts Possible

Setup Late Week-Weekend

As the aforementioned front stalls, a jet stream dip will dig south across the eastern states. This will allow one or more waves of low pressure to develop along the front, helping to pull more rain into parts of the East.
At the same time, strong high pressure in eastern Canada will help create a large pressure gradient along the East Coast, increasing the potential for strong winds, coastal flooding, high surf and beach erosion.
It's possible that energy and/or moisture from Tropical Storm Joaquin in the western Atlantic could also play a role in the heavy rain and coastal impacts we see late this week and into this weekend. As mentioned earlier, regardless if that happens or not, we will still see significant impacts in portions of East, however uncertainty remains with the exact details.
Several potential impacts are on the table starting the second half of this week, including:
Rainfall/Flooding: River flooding and flash flooding are both possible in parts of the East. There is uncertainty regarding where the heaviest rain may occur, so areas from New England to West Virginia, Virginia, North Carolina and possibly parts of South Carolina should continue to monitor the situation. Keep in mind that this is several days away and is subject to change.
Increasing Winds: The gradient between lower pressure near the stalled front and a strong area of high pressure anchored from eastern Canada into the Midwest will help increase winds late this week. Depending on how this weather pattern unfolds, the strong winds could impact coastal areas of the Northeast and Mid-Atlantic starting Wednesday night and then last through this weekend. The wind direction may shift during this event as it evolves.
Coastal Impacts: The winds could contribute to high surf, beach erosion and possible coastal flooding in some locations along the Northeast and possibly the Mid-Atlantic coast. At this time, uncertainty is high with where this threat may be the greatest.
Check back with weather.com for updates in the days ahead as we provide more specifics on this forecast.

MORE: Retired Atlantic Hurricane Names