Extreme tropical downpours to unleash life-threatening flood risk in Northeast
Flood-weary parts of the region face renewed risks, and major cities from Boston to New York City and Philadelphia, could bear the brunt of excessive rainfall and the resultant dangers.
Rounds of showers and thunderstorms will target the Northeast, renewing the flood risk and disrupting outdoor plans through next week.
Extreme tropical downpours and locally severe thunderstorms will return to the flood-weary Northeast from late this week into early next week. As more rain pours down on the saturated ground, the potential for life-threatening and highly disruptive flooding will unfold in some areas recently inundated and expand to other locations that have dodged high water thus far, AccuWeather meteorologists warn.
Rainfall rates of up to 3 inches per hour and an AccuWeather Local StormMax™ of 14 inches, with totals likely to fall within 6 hours at some locations, could result in significant flash flooding and urban flooding.
"Whenever rain falls at a rate of 2-3 inches per hour, rain is falling too fast and too furious, and flash flooding will ensue – especially if that cloudburst occurs in an area with already saturated ground from previous heavy rain," AccuWeather Chief Meteorologist Jon Porter said.
A large storm swirling across Canada will help multiple disturbances in the jet stream to pivot around the system, like spokes in a giant wheel, and cause showers and thunderstorms to sweep across the Midwest and Northeast through Tuesday. Plenty of moisture from the Gulf of Mexico and the Atlantic will add fuel to the setup as storms overspread the Northeast.
The storm that swamped the region from this past Sunday to Monday behaved more like a tropical system as it produced rainfall rates ranging from 1–3 inches per hour, according to AccuWeather Senior Meteorologist Dave Dombek.
"[Ocean] water temperatures in the mid-Atlantic region are several degrees above average this summer and are currently more like levels sometimes seen in late August, which is typically the peak of the warmth," Dombek stated. Water temperatures ranged from the mid-70s to the low 80s F and were 3–8 degrees above average early this week.
The warm Atlantic waters will once again contribute to the dangerous flooding risks in the Northeast.
"At the same time, the disturbances from the Midwest will tend to slow down and pivot northward rather than progress quickly out to sea upon reaching the Atlantic coast," Dombek said. "This action will cause much more rain to be unloaded on some areas as opposed to a storm system that continues to move right along."
The setup for the upcoming waves of torrential rain is not likely to occur in exactly the same areas as the recent event, which unloaded 5–10 inches of rain and locally higher amounts from parts of Pennsylvania to eastern New York and Vermont. The upcoming situation is also likely to unfold as multiple smaller-scale events. However, the region is being put on alert by AccuWeather forecasters as repeated episodes of rain into next Tuesday could cause serious and life-threatening flooding.
At times, a plume of moisture will extend from the Atlantic Ocean to the Northeastern states. This setup is sometimes referred to as an atmospheric river.
At least three rounds of downpours and thunderstorms will likely progress slowly from the central Appalachians to the mid-Atlantic coast and New England.
The first will swing through the region into Friday. On Friday, the potential for storms packing heavy rain and flash flooding will extend from New England to the Interstate 95 corridor of the mid-Atlantic region.
The second round is likely to advance across the area from Saturday to Sunday.
"That second round of heavy rain and thunderstorms could result in flooding problems in areas that were largely missed by the system from this past Sunday to Monday," Porter said. "It is possible that cities from Philadelphia to New York City and perhaps Boston are hit by flash flooding this weekend."
Porter also highlighted that when such extreme rainfall rates occur in urban areas, flash flooding with rapidly rising water can quickly escalate into a life-threatening situation in a matter of minutes, as urban environments have many impervious surfaces, such as sidewalks and streets, which promotes greater runoff.
At this time, it appears the greatest risk for flooding rainfall around New York City will be from late Saturday night to Sunday and around Boston during the day and evening on Sunday. Torrential rain may be more spotty farther to the southwest, but cities from Washington, D.C., to Philadelphia along I-95 could be hit with some of the most significant rain of the entire weather pattern during this weekend.
A third round of heavy rain is projected to unfold from Monday into Tuesday.
As more rain falls on a progressively wetter landscape, the risk of small stream flooding and rises on some of the rivers will increase. Small streams and rivers that are already running high could spill out of their banks. Similarly, some streams which experienced flooding recently in Pennsylvania, New York, Vermont and other states could flood again.
One major waterway that bears watching is the Connecticut River. Only part of the Connecticut basin was hit with torrential rain from Sunday to Monday. Should the event unfold as AccuWeather meteorologists are predicting this weekend, the remaining half of the basin will be hit with torrential rain. Some areas that were flooded at the start of the week will also face renewed or exacerbated flooding. This could push the already swollen river to major flood stage next week.
AccuWeather forecasters emphasize that it will not rain continuously everywhere through Tuesday. In fact, much of the time during the six-day period may be rain-free. However, when it does rain, it may pour for several hours and deposit several inches of water during that time. Rainfall of this intensity is more than enough to overwhelm storm drains and lead to street flooding and rapid rises along small streams.
Major metro areas like New York, Boston, Philadelphia, and Washington, D.C., are among the places that could bear the brunt of the excessive rainfall. Travel could be brought to a standstill for several hours in these locations, AccuWeather meteorologists warn.
Forecasters urge those who live along small streams to closely monitor weather alerts. Heavy rain that occurs miles upstream can trigger a flash flood downstream in an instant.
A general 1–4 inches of rain is likely to fall on the Northeast from Thursday through Tuesday. However, there will be pockets of 4-8 inches of rain with an AccuWeather Local StormMax™ of 14 inches. This is on top of the rain that fell from this past Sunday to Monday.
Severe weather to add to the dangers
Another component of the wet and active weather pattern will be rounds of locally severe thunderstorms through the end of the week, especially during the afternoon and evening hours.
The threat of severe weather will focus on much of the I-95 corridor of the mid-Atlantic, parts of upstate New York and New England late Friday into Friday night.
As each disturbance swings through, a new round of severe weather will be possible from the Appalachians and eastern Great Lakes region to the mid-Atlantic coast and parts of New England.
Meanwhile, additional threats for severe weather are expected to unfold in the central U.S. through the weekend. The same storm expected to bring severe thunderstorms to the Plains could bring another dose of severe weather to the Ohio Valley and Midwest over the weekend.
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