Topline
Sweltering heat in the Northeast broke early Thursday morning but the cold front slowly working its way across the region has brought an increasing flood threat to the mideast, including Philadelphia, Baltimore, New York City and Washington, D.C.
The National Weather Service has issued flood watches in parts of Virginia, Maryland, Pennsylvania, New York, Connecticut, Delaware, Rhode Island and New Jersey.
A warm and humid airmass that moved across the area ahead of the cold front is expected to develop into rain and thunderstorms Thursday night, which could bring up to 7 inches of rain to some parts of New Jersey, Delaware and Pennsylvania.
The NWS warns the heavy rainfall could lead to excessive runoff that could flood rivers, creeks and streams, leading to flooding in urban areas with poor drainage. While cool rain falls on the northeast, the southeast is under heat advisories and extreme heat warnings.
The extreme heat warnings impact Arkansas, eastern Tennessee, Mississippi and Louisiana, with advisories extending to parts of Oklahoma, Texas, Alabalama, Georgia, Florida, South Carolina and North Carolina.
The heat index could be as high as 116 degrees in portions of southeast Georgia and southeast South Carolina through 8 p.m. Thursday.
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An increase of flash flooding events swept the country this summer as intense rainfall, increased moisture in the atmosphere and changing landscapes led to more disastrous floods impacting more people. A slow-moving storm brought over a foot of flooding to central Texas and pushed Guadalupe River levels up 27 feet in less than an hour, swamping the area of Kerr County and killing more than 130 people on July 4. Three people are still missing. In North Carolina, Tropical Storm Chantal flooded the Eno River and killed six people and, in New Mexico, at least three people died in floods in the mountain village of Ruidoso.
Flash floods are always more common in the summer months, when daytime heat helps fuel thunderstorms. Warmer air also holds more moisture, which can drive up rainfall amounts. The storms in North Carolina and Texas, for instance, were fueled by high levels of atmospheric moisture brought by Tropical Storms Berry and Chantal, respectively. Summer storms move more slowly than in other seasons, leaving rain to pile up in the same place instead of spreading across a wider surface area. Climate change is also to blame for worsening the already ideal conditions. Global warming means more evaporation, which increases moisture in the atmosphere, and heatwaves before heavy rain can dry out the landscape, leaving it less able to absorb large amounts of water when it rains, according to the Environmental Defense Fund.
Yes. The proportion of people across the world living in flood-prone areas has risen by 20% to 24% since 2000, according to NASA, and climate change is driving extreme rainfall and more intense hurricanes. Rising sea levels also increase tidal flood risk and storm surge, resulting in deeper floods that travel farther and last longer, according to the First Street Foundation.