Researchers Forecast Increased Hurricane Activity And Less Predictability

According to Anthony Lupo, MU assistant professor of atmospheric sciences, and Grant Johnston, an undergraduate student in atmospheric sciences, long- and short-term changes in the surface temperature of the Pacific Ocean have an impact on the occurrence and intensity of Atlantic Ocean hurricanes.

The researchers examined the variability of hurricane intensity from 1938 to 1999 using data compiled by Colorado State University's Tropical Meteorology Project Archive. They then compared this data with the occurrence of El Nino and La Nina events and the two phases of the North Pacific Oscillation (NPO), a 50- to 70-year sea surface temperature variation.

"The NPO is like a giant, long-lived El Nino," Lupo said. "The first phase, NPO1, is characterized by warmer surface temperatures in the Eastern Pacific and lower surface temperatures in the Western Pacific. The second phase, NPO2, exhibits the reverse conditions."

Lupo added that although previous research has shown there are fewer hurricanes during an El Nino year than during a La Nina year, few studies have examined how El Nino and La Nina variability affect the intensity of hurricanes. "Our research not only addresses this issue, but superimposes these findings on variability associated with the NPO," he said.

After analyzing the 62 years of hurricane data, Lupo and Johnston arrived at the following conclusions:

-- Hurricane occurrence and intensity are higher during La Nina years.

-- El Nino effects are enhanced by the NPO1, causing fewer and less intense hurricanes during El Nino years.

-- El Nino-related variability is not evident during the NPO2 phase.

-- In general, hurricane occurrence and intensity has been higher during the NPO2 phase. Scientists believe the NPO now has shifted back into the NPO2 phase.

"Because the 2000 season will exhibit the effects of La Nina, we can expect a greater number of hurricanes and a chance for more severe hurricanes," Lupo said. "But due to the influence of the NPO2, this season lacks any predictability."

The National Weather Digest has accepted Lupo and Johnston's paper, which is scheduled to be published later this year.