Hurricane season jumped the gun this year, with short-lived Tropical Storm Alberto spinning up off South Carolina and forecasters monitoring a mass of storms that had drenched South Florida for days.
That puts one tropical storm on the books before the six-month season ‘officially’ begins today (June 1).
Fortunately, a fast start doesn’t necessarily point to a hectic hurricane season.
Federal forecasters on May 24 predicted a near-normal season ahead — likely on the low side of average if an El Nino weather pattern develops, but higher if it does not.
The National Oceanic and Atmospheric Administration’s annual pre-season forecast calls for a likely range of nine to 15 named storms, with four to eight becoming hurricanes.
Of those, one to three are expected to turn into major storms.
Since 1981, an average season has produced 12 named storms with six hurricanes, three of them becoming major storms with Category Three winds of 111 miles per hour or higher.
Although the storm count might be down a bit from the hyperactive seasons of the past decade, forecasters pointed to Hurricane Andrew 20 years ago as evidence that it takes only one landfall to produce a disastrous hurricane season. Andrew, a Category Five hurricane with 165 mph winds, caused $25.5 billion worth of damage when it raked South Miami-Dade on August 24, 1992.
“Just because we predict a near-normal season doesn’t mean anyone is off the hook at all,” said Gerry Bell, lead seasonal forecaster for NOAA’s Climate Prediction Center.
Ocean and atmospheric factors have fuelled increasing hurricane activity since 1995, including near-average temperatures in the Atlantic Ocean and Caribbean Sea, said Dr Bell.
But the potential formation of El Nino is a wild card that has added uncertainty and widened the range of predicted storms, he said. That weather pattern, marked by warming Pacific Ocean temperatures, typically tends to quieten the tropics in storm numbers and intensity— in part by feeding upper-level wind that can weaken forming storms or sometimes rip them apart.
If an El Nino forms, it would likely help keep the storm count at the lower end of the forecast range, although computer models remain split on whether the pattern will build later this summer, he said.
NOAA’s prediction, announced at the agency’s Atlantic Oceanographic and Meteorological Laboratory on Virginia Key, was similar to a number of other experts’ pre-season estimates.
Dr Bell said the formation of Alberto, the third tropical storm to form before June 1 in the past 31 years, was an “unusual” occurrence but no indication of the season ahead.
The vast majority of storms form from waves rolling off Africa.
NOAA does not make landfall predictions, but during past ‘active to very active’ years, there has been a 90 per cent chance of a strike somewhere along the East Coast and an 80 per cent chance of a Gulf Coast landfall.
The odds of multiple strikes also go up during active years, as do the risk factors for Caribbean countries.
South Florida hasn't been hit by a major hurricane since Wilma in 2005, a record-breaking year that produced the most storms (28) and hurricanes (15), seven of them reaching major status.