Within the last few days Colorado State University, an institution known for its extended range hurricane forecasts, issued its forecast for the 2015 Atlantic hurricane season, which runs from June 1 through November 30. Their current forecast predicts one of the quietest hurricane seasons in years, with seven named storms, three hurricanes and one major hurricane. A major hurricane is defined as having one minute sustained wind speeds in excess of 110mph.
While forecasts like these are hugely helpful, they can inadvertently cause complacency to set in the minds of the people most likely to be affected by a hurricane. Understanding how they form, and learning the lessons that history has taught us, is therefore very important.
The reason behind the below normal activity forecast is two-fold: The Atlantic is neither much cooler nor much warmer than average, and an El Niño, which was officially declared to be underway by NOAA in February, is on-going in the Pacific. Hurricanes thrive over warm sea surface temperatures, so when sea surface temperatures are cooler in the eastern tropical Atlantic they act as a deterrent to any tropical wave coming off of Africa.
Conditions in the Pacific Ocean also are not favorable for Atlantic hurricane development. NOAA officially declared an El Niño event to be on-going in February. El Niño events in the Pacific lead to an increase in wind shear over the tropical Atlantic, the area of hurricane development. Wind shear is the change in wind speed and direction with height, and as wind shear increases, the thunderstorms that are such an integral component of hurricane structure get torn apart, and the hurricane ceases to intensify. NOAA gives a 60 - 70% probability that El Niño conditions will still be present in the Summer and Fall of 2015 in the Northern Hemisphere.
However, the forecast for an inactive season should not lead to apathy. It's important to remember that it only takes one event to make a catastrophe, and the US is going on year #10 without a major hurricane landfall. Without wanting to tempt fate, you could argue that we are due an event…
Populations have short memories, but a lull in activity should not lead to the conclusion that the risk is permanently reduced. All coastal residents and governments should have plans in place to cope with, and recover from, a landfalling hurricane. History shows that other years with reduced hurricane activity have also featured some of the more damaging Atlantic hurricanes. An El Niño event was on-going in 1957, and only 7 named storms formed. One of these storms was Hurricane Audrey, which caused 416 deaths in the Gulf Coast, making it the 6th deadliest hurricane to hit the continental United States.
Perhaps the most notorious reminder of, "It only takes one storm to make a disastrous hurricane season," is the year 1992. A moderate to strong El Nino was present during the 1992 hurricane season, and the year got off to a very late start. The first named storm didn't form until August 16th, well past the average date of the first storm formation. That storm was christened Andrew, and Andrew would eventually go on to make landfall as a Category 5 hurricane in South Florida, breaking records and devastating Dade County. Ultimately, 6 named storms formed in 1992, but only one mattered.
Category: Climate/natural disasters: Disaster risk, Floods/storms, Resilience
Location: United States