A near- to below-normal Atlantic hurricane season is now expected as the calming effects of El Niño, a periodic warming of central and eastern tropical Pacific waters, continues to develop. But scientists at the National Oceanic and Atmospheric Association (NOAA) say the season’s quiet start does not guarantee quiet times ahead.
The season, which began June 1 and was expected by NOAA to be average, is entering its historical peak period of August through October, when most storms form. Thus far, no tropical storms have formed this summer.
“While this hurricane season has gotten off to quiet start, it’s critical that the American people are prepared in case a hurricane strikes,” said Commerce Secretary Gary Locke.
NOAA’s Climate Prediction Center, a division of the National Weather Service, now predicts a 50 percent probability of a near-normal season, a 40 percent probability of a below-normal season, and a 10 percent probability of an above-normal season. Forecasters say there is a 70 percent chance of seven to 11 named storms, of which three to six could become hurricanes, including one to two major hurricanes (category 3, 4 or 5). The main change from NOAA’s initial outlook in May is an increased probability of a below-normal season, and an expectation of fewer named storms and hurricanes.
The May outlook called for nine to 14 named storms, of which four to seven could become hurricanes, including one to three major hurricanes. During an average season, there are 11 named storms with winds of at least 39 mph, of which six become hurricanes with winds of 74 mph or greater and two of those become major hurricanes with winds of 111 mph or higher.
In recent weeks, forecasts for the return of El Niño have come to fruition. Indications of an El Niño have been emerging for about the past two months from satellite pictures and an array of robotic buoys strung out across the Pacific. NOAA’s Climate Prediction Center noted weekly eastern equatorial Pacific sea surface temperatures were at least 1.0 degree Celsius above average at the end of June and July.
El Niño can include weaker trade winds, increased rainfall over the central tropical Pacific, and decreased rainfall in Indonesia. In the United States, it typically suppresses hurricane activity, brings beneficial winter precipitation to the arid Southwest, less wintry weather across the North, and a reduced risk of Florida wildfires.
“El Niño continues to develop and is already affecting upper-level atmospheric pressure and winds across the global tropics,” said Gerry Bell, Ph.D., lead seasonal hurricane forecaster at NOAA’s Climate Prediction Center. “El Niño produces stronger upper-level westerly winds over the Caribbean Sea and tropical Atlantic Ocean, which help to reduce hurricane activity by blowing away the tops of growing thunderstorm clouds that would normally lead to tropical storms.”
Still, NOAA cautions about not being prepared.
“El Niño may mean fewer storms compared to recent seasons, but it doesn’t mean you can let your guard down,” said Jack Hayes, Ph.D., director of NOAA’s National Weather Service. “History shows that hurricanes can strike during an El Niño.”
According to data from the National Hurricane Center, the calm start to the 2009 hurricane season is not a reliable indicator of the overall activity for the entire season. On average only one or two storms form during an Atlantic Hurricane Season’s first two months and the 1992 Atlantic hurricane season, for example, had a below-normal number of named storms and hurricanes and still had dangerous activity. The first storm did not form until late August that year, when Hurricane Andrew hit southern Florida as a destructive Category 5 storm. Andrew caused 15 deaths directly, 25 deaths indirectly and $30-billion in property damage, making it the costliest disaster in United States history.
The Federal Emergency Management Agency (FEMA) admits that modern technology, which aids NOAA in predicting hurricanes, has helped to suggest how many storms will form but not predict when disasters such as Andrew will occur. “NOAA’s outlooks are extremely valuable when determining cycles and trends for the season, however they don’t tell us when the next storm will occur or where it may strike,” said FEMA administrator Craig Fugate. “It only takes one storm to put a community at risk. That is why we need to take action and prepare ourselves and our families before the next storm hits, including developing a family disaster plan. By taking a few simple steps now we can help ensure that we are better prepared and that our first responders are able to focus on our most vulnerable citizens.”