Philadelphia and Delaware hit by rainfall 1 000 percent of normal during Isaias, U.S.

Last week's rainfall brought by Tropical Cyclone "Isaias" was almost 1 000 percent of normal in parts of Philadelphia and Delaware. During the same period, three tornados were confirmed in Delaware, wherein the annual average is only one. On Thursday, August 13, 2020, the National Weather Service (NWS) warned that a front will bring another bout of heavy rains and thunderstorms to the Mid-Atlantic region.

The agency confirmed that a twister touched down in Milford, Sussex County, and crossed into Kent County last week, during the height of storm Isaias. It was Delaware's third tornado in a week — the state usually records only one in a year.

"This EF-1 tornado occurred in Milford, Delaware, and this brings the total number of tornadoes to three in Delaware from the tropical storm [Isaias]," said NWS Mount Holly.

The storm struck on August 4 with maximum winds of 161 km/h (100 mph). Based on the preliminary damage survey results, its path length stretched 4.3 km (2.7 miles) and had a maximum width of 366 m (1 200 feet). No injuries were reported.

Overall, NWS confirmed eight Isaias-related twisters, including one in Maryland.

In Delaware County, last week's countywide average was 947 percent of normal as more than 200 mm (8 inches) fell on the area in a seven-day period, according to the River Forecast Center in State College, Pennsylvania.

In Chester County, more than 250 mm (10 inches) was recorded in West Chester, which was 850 percent of average.

Last week's deluge was nearly 1 000 percent of normal in parts of Philadelphia, according to the Middle Atlantic River Forecast Center.

An Inquirer analysis of NWS data found Wynnewood with the highest amount of rain at 218 mm (8.6 inches), among 247 locations in Pennsylvania, New Jersey, and Delaware. 

As of Thursday, a lingering front is expected to bring another round of heavy showers and thunderstorms to the Mid-Atlantic. NWS warned of a slight risk of excessive rainfall over parts of the region, as well as in Lower Mississippi Valley.

"A front will become quasi-stationary over the Northeast/Mid-Atlantic into the Ohio Valley into Friday (August 14)," the agency said.

"A Slight Risk of excessive rainfall exists over the Mid-Atlantic through Friday morning due to recent and expected heavy rainfall; the Slight Risk means there will be mainly localized scattered flash flooding over the region."

The system will sag southward late Friday as high pressure builds southward from eastern Canada. 

Featured image credit: NBC10 Philadelphia