By Eric Berger, MCT
After two extremely active Atlantic hurricane seasons, forecasters are predicting a quieter season than normal.
With optimal conditions across much of the Atlantic, 19 named storms formed in both 2010 and 2011.
This year, though, storm development should be hampered by uncharacteristically cool sea surface temperatures and the potential development of El Nino.
For these reasons, in their initial report released last month, seasonal forecasters Bill Gray and Phil Klotzbach predicted that 10 named storms would form, with just four becoming hurricanes and two developing into major hurricanes.
The median number of named storms — tropical storms and hurricanes — during Atlantic hurricane seasons since 1980 is 12, including 6.5 hurricanes and two major hurricanes.
In some ways, predicting a slightly below-normal season is remarkably bold.
That is because, since 1995, the region of the Atlantic Ocean where storms form has been warmer, as part of an increase in temperatures caused by an upswing in a natural cycle known as the Atlantic Multidecadal Oscillation.
Since then, Dr Gray and Dr Klotzbach have predicted as few as 10 named storms just three times — in 1995, 1998 and 2001 — and they’ve never predicted fewer than six hurricanes in a season.
“It’s definitely a risk, but given the current set-up in the tropical Atlantic and Pacific, it’s the best we can say,” said Dr Klotzbach.
Chris Hebert, a hurricane forecaster with Houston-based ImpactWeather, believes it is a risk worth taking.
In addition to the cooler sea temperatures and possibility of an El Nino, which increases wind shear that can tear storms apart, Mr Hebert said some forecast models predict higher-than-average air pressures across the Atlantic basin, which includes the Caribbean Sea and the Gulf of Mexico.
Higher pressures would limit storms because they produce sinking air, which inhibits thunderstorm development. High pressures also increase wind shear and bring more cooler water from deep within the ocean to the surface, he added.
“All the signals are there for less named storms than in recent years,” he said. “However, less named storms doesn’t translate into no threat.”
By Ken Kaye, MCT
Climatologists are expecting fewer storms this year but say that is no reason for people to drop their guard in making hurricane preparations.
Phil Klotzbach and William Gray of Colorado State University (CSU) are predicting 10 named storms, which include four hurricanes, two of which will be major (higher than a Category Three).
The average season has 12 named storms, including six hurricanes, three of which are major.
The climatologists expect the tropical Atlantic to be cooler than it has been in recent years.
They also say there is a “fairly high likelihood” that El Nino, the atmospheric force that suppresses storm formation, will develop by the summer.
“Typically, El Nino is associated with stronger vertical shear across the tropical Atlantic, creating conditions less conducive for storm formation,” Dr Klotzbach said.
The last time four or fewer hurricanes developed was in 2009, when three hurricanes formed. Before that it was 2002, when three hurricanes also developed.
Despite the tame prediction, the two CSU climatologists warn that a slow season does not mean a hurricane won’t threaten the US coastline.
“All vulnerable coastal residents should make the same hurricane preparations every year, regardless of how active or inactive the seasonal forecast is.
“It takes only one landfall event near you to make this an active season,” said Dr Klotzbach.
Hurricane Andrew is a prime example of how powerful storms can strike, even in slow years.
The Category Five system devastated southern Miami-Dade County in Florida 20 years ago in 1992 — a year that otherwise saw only six named storms.
Dr Klotzbach and Dr Gray predict that tropical cyclone activity in 2012 will be about 75 per cent of the average season.
In comparison, tropical activity in 2011 — when 19 named storms formed — was 145 per cent of the average season.
As part of their forecast, the CSU team predicts:
• A 42 per cent chance that at least one major hurricane will strike the US coastline. The long-term average probability is 52 per cent.
• A 24 per cent chance that a major hurricane will hit the US East Coast, including the Florida Peninsula. The long-term average is 31 per cent.
• A 24 per cent chance that a major hurricane will make landfall on the Gulf Coast, from the Florida Panhandle west to Brownsville, Texas. The long-term average is 30 per cent.
WSI (Weather Services International), a part of The Weather Channel, also predicts a relatively tame season — although one closer to normal, with 11 named storms, including six hurricanes — two major.
Aside from Hurricane Irene, which struck North Carolina and caused major flooding in the Northeast last year, the US has enjoyed three relatively calm storm seasons.
Prior to Irene, the last hurricane to strike the US coast was Category Two Ike, which struck Texas in September 2008.
Florida, historically the most hurricane-battered state in the nation, also has been extremely lucky.
It has gone a record six seasons without seeing a hurricane strike.
The last hurricane to hit Florida was Wilma in October 2005.
Dr Gray said despite the below-average forecast, the Atlantic basin remains in an era of tropical intensity, the result of a natural cycle.
He said he expects that era “to continue for the next 10 to 15 years or so”.
Hurricane season starts June 1 and runs through November 30.