Quick-forming Virginia Beach tornado left short window for warning system, weather service says
The tornado that ravaged Virginia Beach on Sunday formed in about five minutes, experts said, giving those in its path virtually no time to react.
The early forecast from the National Weather Service office in Wakefield showed only a slight risk of severe weather in the afternoon. Hampton Roads was placed under a thunderstorm warning at 5:24 p.m., and those in the areas around Broad Bay received text alerts of a tornado warning at 5:47 p.m., according to Eric Seymour, warning coordination meteorologist with NWS.
The tornado touched down a minute later at 5:48 p.m., the NWS estimated, and dissipated by 5:53 p.m. after traveling 4.5 miles and reaching wind speeds as high as 145 mph — damaging more than 100 homes. The warning was sent to an estimated 58,362 people in the area, which included eight schools and two hospitals, according to NWS.
No injuries were reported as a result of the tornado.
The meteorologists in charge of sending out warnings closely monitored the increased risk of severe weather but only had a few minutes to interpret the data before sending the tornado alert, Seymour said. Their goal is to send warnings 15 minutes before a tornado touches down.
“In this case you had two (storm) cells that ended up merging together ahead of a cold front and ... you probably have three, four minutes to try to look at everything and make a decision on it,” Seymour said. “That, unfortunately, is a lot of what we get here in the mid-Atlantic states.”
Out west, tornadoes form in more isolated, longer-lasting cells that meteorologists and residents can see much sooner, he added. Seymour explained that the two storm cells combining is among the “triggers” that cause analysts to watch the radar more closely. It creates greater variability of wind speeds and directions, which can quickly produce a funnel cloud.
Once the meteorologists decide to issue the warning, it only takes about 30 seconds to send text alerts and tweet out the warning, Seymour said. About 15 years ago, the NWS sent warnings to entire the county affected by the weather event. But this didn’t work well for states with large counties — or county-sized cities like Virginia Beach — so they switched to issuing warnings based on “polygons” drawn over the area at the highest risk.
The polygon is generated by a computer, and a meteorologist can look at the storm’s trajectory and adjust the shape to include where they think it could travel over the next 30 or 45 minutes. However, only those in the polygon whose phones are compatible with version 3.0 of the Federal Communication Commission’s Wireless Emergency Alerts (WEA) — and have location services enabled — can receive the most precisely targeted text alerts, according to Seymour. Those without location services or with older phones receive alerts if they’re connected to a cell tower that covers an area within the polygon.
“If anything, the older phones a lot of time you were getting warnings when you weren’t in the area where the warning was ... as opposed to being in the alert area but you don’t get it — that doesn’t happen,” Seymour said. “It’s an over-warning scenario, not an under-warning scenario.”
Gavin Stone, 757-712-4806, gavin.stone@virginiamedia.com
