El Nino in central and eastern Pacific

Pacific El Nino Produces Mild Atlantic Hurricane Season

December 2006
As the 2006 Atlantic hurricane season closed Thursday, NOAA scientists said seasonal activity was lower than expected due to the rapid development of El Nino, a periodic warming of the ocean in the central and eastern equatorial Pacific, which influences pressure and wind patterns across the tropical Atlantic.

The 2006 Atlantic hurricane season is considered the quietest in a decade. Only nine tropical storms formed, the last one in early October, and not a single hurricane hit the U.S. mainland.

"The development of El Nino conditions by September helps explain why this Atlantic hurricane season was less active than predicted," said Gerry Bell, NOAA’s lead forecaster on the Atlantic hurricane seasonal outlook team. "El Nino developed quickly and the atmosphere responded rapidly, reducing hurricane activity during an otherwise active era that began in 1995."

Louisiana Governor Kathleen Blanco, whose state was devastated by hurricanes Katrina and Rita last year, gave thanks for this year's uneventful hurricane season.

"I know many prayers have been answered - mine included - up and down the Gulf Coast," said Governor Blanco. "After last year, we needed a break. And, we've put this time of respite to good use by strengthening our protections, upgrading our emergency preparedness procedures, investing in new technology and protections and making sure that all of our communities are safer and stronger."

"We know there will be more hurricanes and other natural disasters," said the governor, "but because of our hard work and determination, Louisiana is better prepared than ever before for the challenges ahead."

Unlike the past three seasons, the stronger hurricanes stayed out at sea, sparing the Americas and the Caribbean islands from major hurricane damage this season.

Only two of the storms - Gordon and Helene - evolved into major hurricanes of Category 3 strength or higher with peak winds of 120 miles (193 kilometers) an hour or more, but both stayed well offshore of the U.S. mainland.

An average Atlantic hurricane season has 11 named storms, with six becoming hurricanes and two becoming major hurricanes.

El Nino, combined with the large-scale weather patterns over the southeastern U.S., produced sinking air in the middle and upper atmosphere, along with higher than anticipated wind shear over the Atlantic Ocean, Gulf of Mexico and Caribbean Sea.

These conditions minimized thunderstorm activity, which inhibited tropical storm and hurricane formation.

Analysis by NOAA scientists has linked El Nino’s rapid development and intensification to a series of large subsurface ocean waves that affect ocean temperatures, which began in June. These waves produced a progressive warming of the tropical Pacific Ocean during the summer months.

A particularly strong wave led to a significant warming of the entire eastern half of the equatorial Pacific in early September. This led NOAA in early September to report that an El Nino had developed.

These warmer waters produced enhanced rainfall near the international date line, resulting in suppressed hurricane activity.

"Getting a quick handle on El Nino events, which rapidly intensify, is essential for predicting seasonal hurricane activity," said Bell.

"The last time we had a rapidly developing El Nino was during the 2002 hurricane season, which also led to near-normal activity," said Bell. "NOAA continues to develop and improve climate models to better predict the onset of El Nino, its impacts on weather patterns in the United States and its effects on Atlantic hurricane activity."