Forecasters predict that the number of significant hurricanes this year will be comparable to 2017, which witnessed the exceptionally powerful hurricanes Harvey, Irma, and Maria.
Since 2014, a model developed by Xubin Zeng, a professor of hydrology and atmospheric sciences at the University of Arizona, and his former doctoral student Kyle Davis has successfully predicted hurricane activity.
“We are not expecting this to be as damaging as 2017,” Zeng says. Nonetheless, he emphasizes that “people should get prepared.”
“This is going to be a very active hurricane season.” That is our message,” Zeng adds, noting that hurricanes normally have the biggest impact on the East Coast and Gulf Coast.
WINNERS AND LOSSERS IN OCEAN BASIN
This year, the researchers predict nine hurricanes, five of which will be significant hurricanes. Historically, there have been seven storms every year on average. According to Zeng, there were ten storms in 2017, six of which were quite devastating. The good news this year is that fewer hurricanes are projected to make landfall than in 2017.
since of the rising eastern Pacific Ocean sea surface temperature compared to prior years, this year will be particularly fascinating, according to Zeng, since there will be a battle between two large ocean basins over which will have a stronger influence on storm activity.
“After a few years of La Nia, we expect a good, nice El Nio to return,” Zeng says.
El Nio and La Nia are two opposing extremes in the equatorial Pacific Ocean’s sea surface temperatures, rainfall, surface pressure, and air circulation. While El Nio denotes an above-average sea surface temperature over the eastern Pacific, La Nia denotes a periodic cooling of sea surface temperature. This year, less storm activity is forecast across the North Atlantic due to El Nio activity, or the warm phase.
At the same time, the ocean surface temperature over the Atlantic this year will be very high, which tends to increase storm activity, according to Zeng.
The forecasting team is unsure which ocean region will emerge as the “winner” of the war and will revise its projections in June.
WINDS DURING HURRICANE SEASON
Hurricanes are powerful storms that form over warm tropical seas. As they move through the moist tropics, they begin as low-pressure areas and then intensify thunderstorm activity. Warm ocean air rises and cools, causing clouds and thunderstorms to form. Water vapor condenses in the clouds and creates droplets, which add fuel to the storm by releasing heat.
Wind speeds of 74 mph or higher within a storm are classed as hurricanes by the National Oceanic and Atmospheric Administration, the federal body in charge of weather forecasting.
Though atmospheric wind is an excellent predictor of individual hurricanes, a recent study published by Zeng and his colleagues found that wind measurements are ineffective for predicting hurricane seasons.
This is because “atmospheric winds do not have a long memory,” according to Zeng. “Today’s wind will change tomorrow or two weeks later, unlike ocean temperature, which remains constant for a long time.”
As a result, the beginning wind state is critical for individual hurricanes. However, for forecasting hurricane seasons in advance, the initial state of the wind is unimportant.
Every year, the researchers publish their hurricane predictions in April and again in June. Their forecasting in April is based on the seasonal projection from the European Center for Medium-Range Weather Forecasts, an independent intergovernmental agency that generates global numerical weather forecasts. Zeng’s research team uses machine learning to analyze the European organization’s forecast.
Forecasters employ a combination of forecasting model output and observational data from March through May in June. This is the ninth year in a row that University of Arizona researchers have forecasted hurricanes.
“One of the reasons for our early success is that we actively tune and revise our model every year,” Zeng explains.
Geophysical Research Letters published the findings.