Hurricane experts await emergence of El Nino

Reply Sun 22 Jul, 2012 11:43 am
Jul. 21, 2012
Hurricane experts await emergence of El Nino
By KEN KAYE | Sun Sentinel


El Nino can make the difference between a nasty hurricane season and an easier one. But timing is everything.

Although it's looking more likely that El Nino will emerge this year, scientists still are unsure if it will develop in time to temper the meanest stretch of hurricane season, August through October.

"It could be strong enough to hamper storm formation, but it's not a guarantee at this point," said Phil Klotzbach, the Colorado State University climatologist who develops seasonal predictions.

El Nino, created by an abnormal warming of the Eastern Pacific Ocean, generates strong wind shear that tears apart storms before they get started.

Although computer models unanimously agree the atmospheric pattern will arise over the next few months, it has yet to fully develop, said Mike Halpert, deputy director of the National Oceanic and Atmospheric Administration's Climate Prediction Center in Camp Springs, Md.

"It hadn't reached the threshold in June," he said. "July is going to be close."

How will scientists know if El Nino arrives? In simple terms, the temperature of the Eastern Pacific must warm to 75 degrees, and currently it's 74.5 degrees. It could take a body of water as huge as the Pacific a long time to warm that half a degree, Halpert said.

Technically, El Nino is deemed to have developed when the water temperature is at least 1 degree above the 30-year average temperature of the Eastern Pacific. Further, the water heat must remain steady or continue climb to demonstrate that the ocean isn't experiencing a "temporary blip," Halpert said.

Lastly, scientists must see evidence that El Nino is at play, such as increased winds at upper levels. "We need to see some impact on the atmosphere, or what we call 'coupling,' where the ocean and atmosphere get in sync with each other," Halpert said.

After a furious start to the season, with four named systems, including a short-lived hurricane, the tropics have been dead calm in the past few weeks. However, it's unlikely that El Nino already is kicking in.

"Yes, it's been slow, but in a normal year June and July are typically not very active," Halpert said.

He added that the emergence of the four systems, two of them in May, was a freak occurrence without any real explanation.

To test for El Nino's presence, NOAA primarily relies on satellite observations to measure water temperatures. But it also employs a network of floating and moored buoys and receives data from ships.

In all, dozens of readings are collected daily and analyzed monthly, Halpert said. NOAA releases updates on El Nino's status at the beginning of each month.

When El Nino emerges, it pushes the upper levels winds from west to east, in the opposite direction of tropical waves, which generally move east to west across the Atlantic. Those winds stunt the waves' thunderstorm activity, a necessary ingredient for storms to grow.

"The winds basically sheer off the top of the thunderstorms and inhibit development," Halpert said.

Although storm-nurturing La Nina was in control during the 2011 storm season, resulting in a bustling 19 named storms, it wouldn't be unusual for El Nino to quickly emerge this year, Halpert said. He said the patterns have no specific cycle.

Because it suspected El Nino would develop, NOAA issued a seasonal outlook in late May calling for a near-average year with nine to 15 named storms, including four to eight hurricanes, with one to three of those being major. An average season sees 12 named storms, including six hurricanes, three major. NOAA will update its predictions on Aug. 9.

If El Nino does emerge, it would sharply reduce the odds of a major hurricane striking the U.S. coastline, Klotzbach said.

"Based on data from 1900-2009, the odds of major hurricane landfall along the U.S. coastline are 27 percent in an El Nino year, 45 percent in a neutral year and 66 percent in a La Nina year," he said.

On other hand, he said, powerful hurricanes have hit the U.S. during El Nino years, including Category 4 Betsy, which struck Florida and Louisiana in 1965.

In early June, Klotzbach and colleague Bill Gray predicted 13 named storms, including five hurricanes, two intense, would emerge this year. El Nino's strength will be an important factor when they update their forecast on Aug. 3.

"That's something we're going to be looking at over the next couple of weeks," Klotzbach said.

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