Eastern U.S. Flood Threat to Continue No Matter Where Hurricane Joaquin Tracks
By Chris Dolce
Published Oct 1 2015 03:38 PM EDT
Disastrous Flooding Scenario Possible
Meteorologist Domenica Davis looks at the expected rainfall along the east coast that will likely result in flash floods.
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.
Thursday through this weekend, deep tropical moisture from the Caribbean Sea and the western Atlantic will be involved in this soaking setup as a front stalls near the East Coast. This situation is serious with historic and potentially life-threatening rainfall possible in some locations, especially in parts of South and North Carolina.
Significant impacts are likely in portions of the East, whether Hurricane Joaquin tracks towards the United States or not, 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.
In many areas, the ground is already saturated due to heavy rain that fell earlier this week. The heavy rain that impacted northern New England on Wednesday has since moved out of the area. This batch of moisture-rich air came from the Gulf of Mexico and fueled torrential downpours along a slow-moving cold front. This brought significant flooding to parts of Virginia, New York, North Carolina, Maine, Maryland, Pennsylvania and Ohio.
Rainfall Totals End of September
Shaded areas indicate estimated rainfall totals and plotted amounts are rainfall totals from airport sites and co-operative observers from Sept. 23-30.
Several daily rainfall records were set on Wednesday in New England, some of which include Portland, Maine with 5.56 inches (previous record was 2.14 inches in 1920), Boston, Massachusetts with 2.46 inches (previous record was 1.26 inches in 1899) and Providence, Rhode Island with 2.02 inches (previous record was 0.95 inches in 1946).
Current Radar
Current radar, along with any valid flash flood warnings (green outlines), severe thunderstorm warnings (yellow) or tornado warnings (red). Image updates every 5 minutes; refresh your browser for the latest image.
Thursday Through This Weekend: More Heavy Rain; Wind, Coastal Impacts Possible
As the aforementioned front stalls, a jet stream dip will dig south across the eastern states and an upper-level area of low pressure will develop in the Southeast. This will allow one or more waves of low pressure to develop along the front that will tap abundant tropical moisture, helping to pull more rain into parts of the East.
Setup Late Week-Weekend
The white lines in this graphic are isobars showing the gradient between high pressure in Canada and lower pressure near the front. Also shown is the sharp jet stream dip. Orange, red and purple shadings illustrate tropical moisture.
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 gusty winds, coastal flooding, high surf and beach erosion.
The rain and coastal impacts would begin in advance of any threat from Hurricane Joaquin. Uncertainty remains high on where Joaquin will eventually track. However, even if the center does not make a direct hit on the U.S., rich tropical moisture will still be involved in the soaking setup in the East. For more details on the uncertainties with Joaquin, click the link below.
Here are the potential impacts on the table starting Thursday and lasting through this weekend, no matter whether Joaquin approaches the U.S. or not:
Rainfall, Flooding: River flooding and flash flooding are both likely in parts of the East. There is uncertainty regarding where the heaviest rain may occur; however, areas from the Mid-Atlantic to the central Appalachians and the Carolinas appear to be the epicenter for the heaviest rainfall amounts. Totals could exceed 5 inches in many locations, with some areas having the potential to see more than a foot of rain. Areas farther north into New England should also monitor this situation as well.
Flash flood watches have been issued by the National Weather Service from Maryland southward into most of Virginia, the Carolinas, northeastern Georgia and eastern Tennessee. The National Weather Service office in Greer, South Carolina stated in their forecast discussion Thursday afternoon that a "historic and potentially life-threatening rainfall event is expected this weekend."
Inland Flood Alerts
The latest flood watches and warnings issued by the National Weather Service across the region. These alerts pertain to freshwater flooding resulting from heavy rainfall.
Rainfall Forecast: Next 7 Days
Forecast rainfall, in inches, for the next seven days. Given the uncertainty surrounding the future of Joaquin, the region and magnitude of the heaviest rainfall is likely to change somewhat in future forecasts.
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 right through this weekend. If Joaquin approaches the U.S. coast, there will be a core of much stronger winds, but that remains uncertain.
The National Weather Service has already hoisted high wind watches valid Friday and Saturday for parts of southern New Jersey in anticipation of this windy setup, which could produce gusts of 50 to 60 mph.
Coastal Impacts: The winds could contribute to high surf, beach erosion and coastal flooding in some locations along the Northeast and the Mid-Atlantic coast.
Coastal Flood Alerts
A look at the coastal flood watches, warnings and advisories issued by the National Weather Service along the East Coast. These pertain to flooding caused by seawater pushed onshore by the wind, i.e., storm surge.
The National Weather Service has issued coastal flood watches for the Atlantic coastline from the New Jersey shore south to Virginia Beach and portions of the Carolinas, including the beaches of Delaware and Maryland, and for areas surrounding the lower Chesapeake Bay.
According to the watch bulletins, major coastal flooding may occur along the Atlantic coast of the Delmarva Peninsula as well as the Atlantic-facing coastlines of Cape May and Atlantic counties in southern New Jersey. This means flooding may be severe enough not only to flood numerous roads in coastal areas, but also to flood homes and businesses.
Major coastal flooding may also affect portions of the Virginia Tidewater, including the Hampton Roads metropolitan area encompassing Norfolk, Virginia Beach, Portsmouth, Newport News, and other nearby cities in southeastern Virginia.
Timing of the Rain
This will be a prolonged heavy rain event that will result in rainfall totals over 6 inches over a large area and some locations will likely measure over a foot of rainfall through Sunday. The soil is already saturated in many of the areas expecting heavy rainfall and may lead to dangerous flooding. Landslides and debris flows are also a threat this weekend.
Thursday Night: Widespread heavy rain is expected to begin tonight from Georgia into the Carolinas and Virginia, as well as into eastern Maryland and Delaware. The heaviest rainfall is likely in southeastern Georgia into eastern South Carolina, eastern North Carolina and southeastern Virginia.
Thursday Night's Forecast
Friday: Heavy rain will spread farther north and west during the day, with moderate to heavy rain likely from New York City to Washington, D.C. and through Virginia, West Virginia, and into the Carolinas and parts of Georgia. At this time, the heaviest rain will likely be in portions of North and South Carolina where torrential rainfall is possible.
Friday's Forecast
Saturday: Widespread moderate to heavy rain will impact areas from eastern Georgia through South Carolina, North Carolina, Virginia into West Virginia, eastern Kentucky, southeastern Ohio and southwestern Pennsylvania. Locations as far north as southern New York will see lighter rainfall.
Saturday's Forecast
Sunday: The area expecting heavy rain will shrink and be focused mainly from South Carolina into North Carolina and parts of Virginia. However, showers will remain possible for much of the Southeast and Mid-Atlantic.
Sunday's Forecast
A drying trend is expected to begin early next week across the East.
Check back with weather.com for updates in the days ahead as we provide more specifics on this forecast.