SciTech

What’s the prediction for hurricane forecasting?

A specialist at the National Hurricane Center, in Miami, tracks Hurricane Danny on a computer screen as it becomes the first of the 2015 Atlantic hurricane season on Aug. 20.
A specialist at the National Hurricane Center, in Miami, tracks Hurricane Danny on a computer screen as it becomes the first of the 2015 Atlantic hurricane season on Aug. 20. Getty Images

All’s been relatively quiet on the Eastern front this hurricane season, confirming N.C. State’s Atlantic forecast in April. But even though Danny came and went with little damage late last month, we’re not in the clear yet: According to About.com, an average of one to two hurricanes make landfall on the East Coast each year – with 16 percent of those hitting North Carolina and 11 percent South Carolina.

Rapidly evolving forecasting models increase our chances of preparedness for the six-month season that ends Nov. 30. We talked with state, regional and national experts about the science of predicting.

Q: What forecasting advances have been made since Katrina 10 years ago?

A: Improvements in observation systems – especially in research aircraft – and more sophisticated data for projections have been prominent. “There are NASA satellite sensors with much higher spatial resolution today as compared to 2005,” said Venkat Lakshmi, a professor and hydrometeorology expert at the University of South Carolina. Also, “input into numerical models, the boundary layer and initial conditions has improved, making predictions much better. As a matter of fact, now we have five-day forecasts as compared to three-day forecasts in 2005.”

According to N.C. State grad Michael Brennan, senior hurricane specialist at the National Hurricane Center, steady improvements in track forecasting will soon yield even better preparedness: “The biggest change coming in the next two to three years will be the issuance of watches and warnings specifically for storm surge, which has the greatest potential to kill large numbers of people in hurricanes.”

Q: How do we know forecasting models are becoming more accurate?

A: The proof’s in the numbers, said Matthew Eastin, professor in the Department of Geography and Earth Sciences at UNC-Charlotte: “The National Hurricane Center conducts ‘forecast verification’ at the end of each hurricane season to assess not only its performance with regard to the official forecasts, but also the performance of each prediction model used to help forecast hurricane track and/or intensity.” Results, published on the NOAA website (www.nhc.noaa.gov/verification), “clearly show an improvement over a five- to 10-year period.”

Q: Global forecasting models predict weather for the entire planet. Why are they generally thought to be the most effective type?

A: Gary Lackmann, professor in N.C. State’s Department of Marine, Earth, and Atmospheric Sciences, said “Global models are good for predicting the track of hurricanes, and they provide the information needed to run more detailed models that cover a smaller area but are centered on (and follow along with) the hurricane. Global models also typically run farther out into the future.”

That said, “Since these models cover such a large area, they cannot provide as much fine-scale detail for an individual hurricane as can a specialized regional model.”

Q. If you see hurricane-like patterns building in a Carolinas location that usually doesn’t have any, does that increase the likelihood of a hurricane?

A: “It depends on where the unexpected activity is in relation to the Carolinas and what the prevailing wind patterns are at that time,” said UNCC’s Eastin.

“Hurricanes affecting the Carolinas often come from the south – southwest, due south, or southeast. If, for example, unexpected activity occurred in the Gulf of Mexico during a period when the prevailing winds were from the southwest, then the ensuing hurricane would make landfall along the northeastern Gulf Coast and traverse across the Carolinas from the southwest.”

Q: What levels of hurricanes are most prevalent in the Carolinas?

A: Steven Pfaff, warning coordinating meteorologist with the National Oceanic and Atmospheric Administration, says the Carolinas typically get off lightly. “On the Saffir-Simpson Scale, which ranks a hurricane’s intensity from 1 to 5 (weakest to highest), the Carolinas typically receive Category 1 storms.”

Tingzhuang Yan, a visiting scholar at Coastal Carolina University in Conway, S.C., said the average wind speed of a Category 1 storm is 74-95 mph. Category 5 storms (hurricanes) reach winds of 155 mph and up.

However, Pfaff warns of anomalies – including Hurricane Hugo in 1989 and Hurricane Hazel in 1954 (both Category 4, averaging 131-155 mph). He says that on average, a hurricane strikes the Carolinas every five or six years; for a major hurricane (Categories 3 or higher), every 18 years.

Q: What’s the long-term outlook for Carolinas hurricanes?

A: Yan says his team’s seasonal prediction model can provide the most likely number and range of landfall hurricanes on the eastern and southern U.S. coastlines, but the model can’t predict landfalls in a specific state-scale area. Mark Malsick, severe weather liaison with the S.C. State Climate Office, said the long-term picture “depends on the global ocean and the global atmosphere. Both are in constant flux.”

UNCC’s Eastin is more definite. “An increase in future hurricane impacts across the Carolinas is a real possibility due to climate change. Currently, the Carolinas are on the second-most hurricane-impacted section of the U.S. coastline (behind south Florida). If an increase in hurricane frequency and/or intensity occurs, as many predict, then it is reasonable to assume the Carolinas would also expect more frequent and/or more severe impacts.”

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