Since Hurricane Wilma in October 2005, the US coastal region has not had a land falling hurricane exceed category 2 strength. With El Niño conditions forecast to continue weakening and a possible La Niña on the way, can the US expect the hurricane drought to continue or could this be an especially active season?
The hurricane season begins June 1st and continues until November 30th. Colorado State University (CSU), a leader in seasonal hurricane forecasts for 33 years, has issued their annual outlook for the 2016 season. Based on statistical models and decades of research, scientists at CSU are predicting average hurricane activity this season with 12 named storms, excluding January’s Hurricane Alex. Out of those storms, 5 are predicted to reach hurricane force strength and 2 are expected to reach major hurricane strength (category 3 or higher), typical for an average season. There is a 50% chance of a major hurricane making landfall along the US coastline, a 30% chance for the East Coast and a 29% chance for somewhere along the Gulf Coast.
Does this mean we will see an end to the hurricane drought? Not necessarily. These forecasts are an estimate for what to expect, and with any seasonal forecast, there are numerous factors that increase uncertainty. One such factor will be the weakening El Niño conditions. Current forecast models predict sea surface temperatures will continue to cool to La Niña level temperatures, meaning we will likely transition from an El Niño to a La Niña by the summer months. Although a La Niña looks likely, a slight shift could cause a drastic change to hurricane predictions.
If a La Nina does occur, it will play a crucial role as we would expect a decrease in two major factors in hurricane development: vertical wind shear and dry air intrusion. High wind shear can rip apart the structure of a tropical cyclone or inhibit the ability for a cyclone to form in the first place. Dry air also weakens or inhibits hurricane formation as it makes the air more stable. During an El Niño year, wind shear and dry air are more common, causing a decrease in hurricane activity as we saw during the 2015 season. The opposite conditions occur during a La Niña year, with a decrease in vertical wind shear and dry air which in turn, increasing hurricane activity.
Map provided by NOAA showing typical La Niña influence on the hurricane seasons of the Atlantic and Pacific
Another factor for this year’s hurricane season will be the unusually cold waters in the North Atlantic Ocean. If the colder ocean temperatures spread further south, sea temperatures in the tropical Atlantic could cool and inhibit hurricane development. With the uncertainty of how the North Atlantic’s colder water will affect the activity as well as the strength or presence of a La Niña, the number of storms this year could vary substantially from what Colorado State University has forecast.
Whether or not this season is above or below average, resident’s along the US coastline should remember that it only takes one major hurricane to cause catastrophic damage. In 1992, the season was considered to be below average, with only 7 named storms, 4 hurricanes, and one major hurricane. However, that one major hurricane became one of the most infamous storms in US history: Hurricane Andrew. The category 5 storm hit South Florida in 1992 causing over $26 billion in damages. Although this season is forecast to be near average, all residents in hurricane prone areas should go over their emergency plans with their friends and family. It’s a good idea to start preparing a hurricane kit complete with water, food, radio and first aid supplies before the season starts.