RICHMOND — After 14 days of tracking a storm named Dorian across the Atlantic, Friday will finally reveal what effect it has on Virginia.
The eye of Dorian will make its closest approach to the U.S. mainland on Friday morning. Which part (or parts) of North Carolina will experience a direct landfall, at what strength, and what kind of erosion will result?
Far from the eye of the storm, gusty 40 to 45 mph winds in Central Virginia could lead to isolated issues with trees and power lines, with more widespread outages possible where stronger winds blow across the peninsulas and Tidewater.
In Hampton Roads, the afternoon high tide will coincide with the peak storm surge and lead to major coastal flooding. Though Dorian is not forecast to top the records, it will bring the highest levels at Sewell’s Point in several years. According to Thursday’s forecasts from the National Weather Service in Wakefield, Dorian’s surge is expected to rival or exceed the flooding from Sandy in 2012 but fall short of the levels seen during Irene in 2011.
Several inches of rain falling across Hampton Roads could be heavy enough to trigger inland flash flooding, as well.
Every hurricane is unique, and each one teaches us something new about what they’re capable of. Yet certain lessons bear repeating each season. Here are a few topics — but not the only ones — that have been part of the discussion in the world of weather forecasting over the past two weeks.
Wind is always just one part of the story: It’s obviously bad news when a storm like Dorian climbs from an 80 mph Category 1 to a 185 mph Category 5 as it bears down. Damage potential is multiplied by orders of magnitude across the Saffir-Simpson scale. But a lowering isn’t universally good news, either.
As storms move northward, we often see them expand in size while losing peak wind speeds near the center. Dorian is one such example. The calm eye of the storm off of South Carolina on Thursday was nearly the size of Dorian’s entire field of hurricane-force winds when it approached the Bahamas. A broadening storm can affect a greater land area and contain more power to slosh storm surge around, so “weakening” isn’t the best word to describe that trend.
And a downgrade from a Category 5 to Category 2 based on slackening winds doesn’t mean much at all when it comes to inland flooding danger.
A hurricane is a region, not a point on a map: The National Hurricane Center’s familiar track forecast cone, or “cone of uncertainty,” predicts where the center of a storm is most likely to track over five days, not necessarily where the effects will be felt. The cone does not expand or shrink based on the level of confidence about an individual storm, but is based on the overall forecast performance from the past five years.
The cone looks smaller than it did during the days of Isabel in 2003 and Irene, because those track forecasts continue to improve on average.
There are exceptions, but the eventual path ends up within the cone about two-thirds of the time.
With Dorian, early forecasts were too far west with regards to its track across the Caribbean. Since clearing Puerto Rico on Aug. 28, however, Dorian has moved within the expected zones.
The path Dorian ultimately took, paralleling the curves of the Southeast U.S. coast, was explicitly predicted by Saturday, and the forecast has performed very well all week.
But hurricanes are complicated storms bearing several unique hazards. Slight nudges in location and timing can trickle down to significant shifts in impacts. It would be nice if one map could perfectly convey all of the threats in specific terms to a wide audience, but the storms are too complicated to allow it. Fostering a better understanding of the strengths and limitations of weather maps is a good place to start.
Climate change is an important consideration, but also a nuanced one: While it’s true that we’ve always been threatened by hurricanes, it’s also true that warmer oceans and a warmer atmosphere will have an effect on their behavior going forward.
Climate change doesn’t cause any single hurricane and the record doesn’t show that they’re getting more frequent so far, but researchers are exploring long-term trends signaling slower, wetter storms and faster intensification. Sea level rise (in our region, an existing trend that’s only worsened by a global acceleration) gradually puts more land area at risk of hurricane storm surge.
In coming months and years, scientists will surely examine the factors that made Dorian one of the most violent on record in the Atlantic, and the patterns that forced it to stall over the Bahamas. As was the case with 2017’s Harvey, attribution studies may be able to shed light on whether it was more likely to occur than it would have been in years past.
Still, storm paths will naturally vary over space and time. Our next quiet Atlantic hurricane season — which will be welcome — shouldn’t fool us about the ongoing need for research and preparedness.