Persistent rain to raise flood risk in part of northeastern US

By Alex Sosnowski, AccuWeather.com Senior Meteorologist

September 29,2016; 8:33PM,EDT

 

 

Persistent downpours will raise the flood risk in part of the mid-Atlantic into Friday, while rain will spread over the rest of the northeastern United States into the weekend.
While the cool and rainy weather into this weekend will have people reaching for jackets and sweaters, some may need to keep an eye on streets and basements for flooding.
Highs will mainly range from the lower 60s F to the middle 70s into this weekend. However, the combination of wind, rain and other conditions will cause AccuWeather RealFeel® Temperatures to be in the 40s and 50s at times.
Storm to raise flood risk in mid-Atlantic
"The slow-moving storm will bring periodic heavy rains to much of the mid-Atlantic through Friday," AccuWeather Meteorologist Edward Vallee said.

"Since Atlantic moisture will be involved and downpours will linger in some areas, there will be a general 2 to 4 inches of rain over the mid-Atlantic states," AccuWeather Senior Storm Warning Meteorologist Rich Putnam said.
There is the potential for a narrow zone of 4 to 8 inches with locally higher amounts, Putnam said.
Flooding can occur despite prior dry conditions.
The bulk of the flooding will be restricted to urban areas and along small streams, Valley stated.
These conditions may be widespread from parts of Virginia, Maryland and Delaware. Gusty thunderstorms with hail will accompany the heavy rain threat in some places. Localized flooding can occur from northern Pennsylvania to eastern North Carolina, with a second pocket in part of the Lower Peninsula of Michigan.

Motorists should anticipate delays during their commutes due to poor visibility and high water during the downpours.
Flash flooding has already closed some roads in parts of Maryland, Michigan and North Carolina.
Baltimore, Washington, D.C., Martinsburg, West Virginia, and Harrisburg, Pennsylvania, are likely to be affected by urban flooding. Isolated urban flooding has occurred as far to the west as Detroit and as far to the south as Fayetteville, North Carolina. Motorists should never attempt to drive through flooded roadways.
Downpours, fog and a low cloud ceiling can also lead to occasional airline delays from Philadelphia to Pittsburgh and Detroit initially but will also spread to areas from New York City and Boston this weekend.
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In addition to urban and stream flooding, some of the rivers in the area will be on the rise. Since most of these large rivers were very low at the onset of the rain, major flooding is not likely. However, minor to moderate flooding can occur along the upper Potomac and Rappahannock rivers, since much of the rain has focused on these watersheds thus far.
Some rain to reach drought areas of New England
Farther north, rain-free weather will hold on over much of New England for a time.
Much of New England and New York state are in need of soaking rainfall due to long-term abnormally dry to extreme drought conditions.
"Some beneficial rain may enter the southern and western parts of these areas by Friday and the balance during the weekend," Vallee said.

Enough rain may fall on parts of New York state and southern New England to get small streams flowing and put a small amount of water back into ponds, lakes and reservoirs. However, the storm will not drop enough rain to completely alleviate extreme drought.
Following the heavy rain into Friday, rainfall over much of the mid-Atlantic is likely to become more sporadic in nature during this weekend.
There is a chance Matthew may track northward enough to impact the weather in the Eastern states later next week.
Minor issues anticipated in coastal areas
In addition to areas of soaking rain and urban flooding, coastal flooding will be possible from Virginia to eastern Massachusetts at times of high tide. Minor to moderate coastal flooding will extend along the Maryland, Delaware and New Jersey coasts with tides running 2-3 feet above normal through Friday.

Because of the proximity of the new moon, astronomical tides are higher than much of the rest of the month.
Winds blowing onshore will push some Atlantic Ocean water and waves toward the coast, which can cause overwash on some low-lying beach roads and sea and bay water to invade some communities.
Since above-normal tides and rough surf will persist for more than a few hours, minor beach erosion is likely.