An Active Hurricane Season Predicted

Authored by IRI on June 2, 2010

by Eric Holthaus

The Atlantic hurricane season has officially started, and the International Research Institute for Climate and Society has issued its updated seasonal hurricane forecast for the region. The results continue to indicate that an above-normal season is very likely. This could spell trouble for highly vulnerable Caribbean nations such as Haiti, still reeling from the effects of a 7.0 magnitude earthquake on January 12, 2010. On top of this, other forecasts point to increased thunderstorm activity for the region as well.

The IRI’s hurricane forecast probabilities are the strongest the institution has ever issued at this point in the season, eclipsed only by a late-season forecast during record-setting 2005. The latest numbers call for a 50% chance of above-normal activity, 35% chance of near-normal activity and a 15% chance for below-normal activity. Put in simpler terms, this means that the chance of having an above-normal year is more than three times the chance of having a below-normal one.

The hurricane forecast issued last week by the National Oceanic and Atmospheric Administration is even stronger, calling for an 85% chance of an above-normal season.

Although the forecast calls for an active season, this doesn’t guarantee that devastation will occur. The seasonal forecasts don’t tell us where, when or if the hurricanes will hit land. They just tell us that we’ll likely see more of them this season, increasing the odds that some inhabited areas will get hit.

Because of the potentially destructive nature of hurricanes and tropical storms, the higher odds are a cause for concern. “Hurricanes can devastate the economies of the Caribbean and Central America,” says Walter Baethgen, who runs IRI’s regional program for Latin America and the Caribbean. “Our hope is that seasonal forecasts and other types of climate information will feed into emergency networks and early-warning systems currently operating in the region.”

To facilitate this, the IRI helped develop a website focused on supplying government staff, relief workers and development agents located in Haiti with the most up-to-date weather and climate forecasts for the country. By making this information available through its ongoing partnerships with the United Nations Office for the Coordination of Humanitarian Affairs and the International Federation of Red Cross and Red Crescent Societies, the IRI hopes to alleviate some of these elevated storm risks for Haiti and ultimately help save lives this hurricane season.

Maarten van Aalst, the associate director of the Red Cross/Red Crescent Climate Centre, says that his organization has alerted its network in Haiti and across Latin America. “The Red Cross/Red Crescent is used to mobilizing quickly around short lead-time forecasts for specific hurricane events, but now also has early-warning information to prepare in advance for what may be a particularly active hurricane season,” he says.

Record Ocean Temperatures
The forecast for above-normal hurricane activity has remained high in part because of the dissipation of the 2009-10 El Niño and increased likelihood for La Niña conditions starting in the fall of 2010. In general, La Niña conditions tend to increase the chances for hurricanes in the Atlantic, while El Niño conditions tend to suppress them.

“But the strongest influence on the forecast has to do with what’s going on in the surface waters of the Atlantic,” says Suzana Camargo, who, along with Tony Barnston, developed IRI’s seasonal hurricane forecasts and have been issuing them since 2003. During April, the surface temperatures in the Atlantic, where the majority of hurricanes develop, rose to nearly 1.5 degrees Celsius above the 30-year average–the highest levels ever recorded. “In fact, April marks the third consecutive month that temperatures in this region of the Atlantic broke long term records,” Camargo says. “This is important because, in general, hurricanes use warm-water temperatures as fuel to grow and get stronger.”

Barnston, IRI’s chief forecaster, says these abnormally high-sea surface temperatures do not bode well for a quiet start to the hurricane season. “Taken in combination with the increased likelihood for a developing La Niña during the latter stages of hurricane season, the entire season may be lengthened this year,” he says.

La Niña conditions, should they develop, would also tend to increase the number and intensity of “regular” Caribbean rainshowers and thunderstorms, which in turn could lead to higher chances of flooding and mudslides.

“La Niña conditions give rain-making clouds a greater chance to turn into the tall, dense cumulonimbus clouds associated with thunderstorms. This is the same mechanism that makes hurricane development more likely,” says Barnston.

The next updated IRI seasonal hurricane forecast will be issued in mid-June.

Eric Holthaus is a staff researcher at the IRI. He works primarily in Latin America and Africa on strategies for managing drought, hurricanes and other climate related disasters.

Description of Atlantic main development region

Red Cross/Red Crescent Climate Centre