Why was this week’s storm so bad in the Triangle? Record heat index fueled its strength
Tuesday didn’t set a record high temperature. It just felt like one.
The highest temperature ever in the Raleigh area, 105 degrees, was recorded in July 2012, according to the National Weather Service.
Tuesday’s high reached 100, which did break the previous record of 99 degrees for the date Aug. 15, which was recorded in 2007.
Tuesday also saw an all-time record high heat index of 115.1 degrees, edging out a 115-degree heat index at Raleigh-Durham International Airport in 2010, according to the State Climate Office of North Carolina.
That heat index helped fuel the strong summertime thunderstorm that pushed through the Triangle Tuesday and left thousands without power, meteorologists say. One fatality was reported when a woman driving through a Durham intersection was killed by a tree falling on her car.
Based on historical records dating back to 1945, Tuesday’s maximum heat index essentially tied the previous all-time record of 115 degrees at that site, which was previously set on July 24, 2010 at 3 p.m.
On both Tuesday and that day in 2010, the reported air temperature was 100 degrees with a lot of humidity, assistant state climatologist Corey Davis said.
Meteorologists told The News & Observer that the high heat index factored in the thunderstorms and high-speed winds that struck the region, knocking out power to tens of thousands of people across the Triangle.
What caused the storm?
The heat index is what the temperature feels like to the human body when relative humidity is combined with the air temperature.
Meteorologists say the heat index can be a better indicator of how intense and dangerous the heat can get.
High humidity also plays a big role, said Jimmy Danco, a meteorologist in the Raleigh office of the NWS.
Severe thunderstorms are more likely with high humidity, which is when the dew point is 55 degrees or higher.
Tuesday’s average dew point across different parts of the Triangle was above 70 degrees.
The dew point determines the temperature the air must be cooled to in order to achieve 100% humidity relative to the temperature. A higher dew point has more moisture in the air and can make it feel muggier outside.
“The humidity provides a lot of fuel for the storms to develop in the summertime,” said Danco. “It was definitely a record-breaking day in terms of heat and humidity. Southern warm and humid air like that can result in what we saw yesterday.”
How fast were winds?
Powerful winds reached speeds ranging from 50 mph to 80 mph across the Triangle.
Wind gusts of 73 mph were recorded near Duke University Hospital with sustained wind speeds of 53 mph.
The wind gusts varied along the path of the storm starting in the western Piedmont, according to Danco.
Wind gusts measured over 50 mph in Guilford and Alamance counties in the Triad and then increased to more dangerous speeds toward Chapel Hill, Durham, northern Wake County, Franklin and Nash counties.
Triangle weather forecast
Here’s the 5-day forecast from the National Weather Service and ABC11.
Wednesday will be sunny, cooler and less humid with a high near 89. The overnight low will be around 71 with a 20% chance of showers and thunderstorms after 2 a.m.
Thursday will be partly sunny with a high near 90. There is a slight chance of showers and thunderstorms until 2 p.m.. The overnight low will be 72.
Friday will be mostly sunny and hot, with a high of 91.
Saturday will be sunny with a high of 88.
Sunday will be sunny with a high of 92.
This story was originally published August 16, 2023 at 4:17 PM.
