Updated Aug. 6, 2020 9:23 AM
AccuWeather meteorologists are concerned that locally heavy and gusty thunderstorms could cause trouble in part of an area in the eastern United States that was hit hard by Isaias on Tuesday; however, a major outbreak of severe weather is not likely.
Isaias blitzed from the North Carolina coast to Vermont in less than 24 hours, and its fast movement allowed the storm to maintain intensity well after landfall. Strong tropical-storm-force winds and torrential rain hit hard and fast in much of the mid-Atlantic and New England, which left millions without power.
The storm produced 4-8 inches of rain with locally higher amounts from northeastern North Carolina to southeastern Pennsylvania and has left the ground saturated.
Some of the trees that did not topple from the force of Isaias' winds may still be unstable and could remain vulnerable for a few days after the storm, due to the soggy state of the soil. The threat of more trees coming down as thunderstorms move through will be a concern for some communities through the end of this week.
While some shower and thunderstorm activity occurred Wednesday evening and Wednesday night in parts of the East, the greatest risk of more coverage of heavy, gusty thunderstorms is on Thursday and Friday.
One batch of storms wasted no time erupting on Thursday as drenching downpours kicked up over parts of Virginia and Maryland before dawn and pressed toward the Delmarva Peninsula and southern New Jersey near and shortly after daybreak. The storms dumped an inch of rain on Salisbury, Maryland, in less than an hour Thursday morning.
After these storms move offshore into the Atlantic, more storms are forecast to erupt farther west over the southern Appalachians and Piedmont areas in Virginia and North Carolina and spread northeastward into the nighttime hours.
"Heavy and gusty thunderstorms are forecast into Thursday evening," said AccuWeather Meteorologist Brandon Buckingham, and the storms could unleash some torrential rains.
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"On the southern edge of the threat zone, storms over the Carolinas are more likely to be slow-moving and drenching, rather than gusty by great numbers," said AccuWeather Meteorologist Brett Rossio.
More storms are forecast to erupt over the mid-Atlantic region on Friday.
The risk of heavy, gusty thunderstorms will spread farther to the north on Friday when compared to Thursday and are expected to reach parts of northern Pennsylvania, northern New Jersey, New York state and New England.
Some of the thunderstorms in the East will be capable of producing an inch of rain in 15-30 minutes. "Rainfall of this magnitude in areas that were hit with several inches of rain on Tuesday can be enough to trigger rapid urban and small stream flooding," Buckingham said.
Forecasters and local officials alike always urge motorists never to attempt driving through flooded areas as the floodwaters may be deeper than they appear. A few inches of water could cause some vehicles to lose traction and float, if not stall the engine. In some situations, the road may have been washed away beneath the water.
The very nature of the downpours produced by the thunderstorms over a small area tends to produce gusty winds, even a phenomenon known as a wet microburst, which is a small area of strong winds produced by the downward force of the downpour. This rapidly descending air then spreads out near the ground. In some situations, there can be wind gusts of 40, 60 or 100 mph in the storms.
AccuWeather storm warning meteorologists estimate the potential for strong wind gusts could be as high as 60 mph in some neighborhoods during Thursday afternoon and evening. Given the wet state of the ground in parts of the East Coast that received the heaviest rains from Isaias, wind gusts of 60 mph could be enough to knock over more trees.
Proper maintenance and the location of trees in urban and suburban areas are both essential. Trimming only one side of a tree to make room for power lines can eventually cause a tree to fall due to the imbalance of the limb canopy.
The roots of trees need to spread out evenly in all directions to help maintain balance and anchoring in the soil.
In areas where roots cannot properly spread out evenly in all directions, such as near sidewalks, driveways and streets, trees may more easily topple in strong winds and saturated soil.
Avoid parking or standing under trees during a storm. In addition to a potential lightning strike, gusty winds could cause the tree or a large limb to fall without notice -- something that was widespread this week as Isaias roared through the I-95 corridor.
A tree uprooted by high winds lays on a fence in Brooklyn Heights Tuesday, Aug. 4, 2020, in New York City as Tropical Storm Isaias raced through the northeastern United States. (AP Photo/David Crary)
The risk of thunderstorms will continue on Friday in much of the same area from the Carolinas to Pennsylvania and New Jersey but will also tend to expand northward into New York state and New England.
These storms may generally not pack the punch the storms on Thursday will threaten, but occasionally garden variety storms can pulse for a brief time during the summer months and produce a flooding downpour and isolated strong wind gusts.
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