Hurricanes Growing More Fierce

[Guest All Natural]

Hurricanes have grown significantly more powerful and destructive over the past three decades, according to atmospheric scientist Kerry Emanuel of the Massachusetts Institute of Technology.

 

In his new analysis of tropical hurricane records, which he reports online today in the journal Nature, Emanuel finds that both the duration of the storms and their maximum wind speeds have increased by about 50 per cent since the mid-1970s. Moreover, this marked increase in the energy release has occurred in both the north Atlantic and the north Pacific Oceans.

 

Unlike previous studies, which have focused on whether hurricanes are becoming more frequent, Emanuel's study is one of the first to ask whether they are becoming more fierce.

 

"It's an innovative application of a theoretical concept, and has produced a new analysis of hurricanes' strength and destructive potential," says Jay Fein, director of the National Science Foundation (NSF)'s climate dynamics program, which funded the research. And that analysis, in turn, "has resulted in an important measure of the potential impact of hurricanes on social, economic and ecological systems,"

 

Indeed, as Emanuel himself says, "the near doubling of hurricane's power over the period of record should be a matter of some concern, as it's a measure of the [future] destructive potential of these storms."

 

Also of concern, he says, is that the increases in storm intensity are mirrored by increases in the average temperatures at the surface of the tropical oceans, suggesting that this warming is responsible for the hurricanes' greater power. Since hurricanes depend on warm water to form and build, Emanuel warns that global climate change might increase the effect of hurricanes still further in coming years.

 

In addition, he says, recent research suggests that global tropical hurricane activity may play a role in driving the oceans' circulation, which in turn has important "feedbacks" to regional and global climate.

 

Fluctuations in tropical hurricane activity "are of obvious importance to society," he adds, "especially as populations of affected areas increase. Hurricanes account for a significant fraction of damage, injury and loss of life from natural hazards, and are the costliest natural catastrophes in the United States. As the human population in coastal regions gets denser, the damage and casualties produced by more intense storms could increase considerably in the future."

[Guest LAW]

The story of Katrina has just begun. Thousands, perhaps hundreds of thousands of

people have lost their homes. Most of the area where the hurricane hits will be uninhabitable for weeks perhaps longer. Water shortages will make human suffering incredible by modern standards.

 

"A lot of people lost their lives, and we still don't have any idea, because the focus continues to be on rescuing those who have survived." - Louisiana Gov. Kathleen Blanco - August 30, 2005

 

“This hurricane has caused catastrophic devastation across areas of Louisiana, Mississippi and Alabama, FEMA, along with our federal, state and local partners, is working around the clock to get live-saving assistance into the hardest hit areas. We need everyone’s cooperation to keep passable roads clear and to prevent those returning from placing additional burdens on the limited shelter, food and water in the heavily impacted areas.” - Michael D. Brown, Under Secretary of Homeland Security for Emergency Preparedness and Response and head of FEMA - August 30, 2005

 

Katrina began as a tropical depression gathering energy from heated water vapor in the atmosphere around the central Bahamas on the afternoon of 23 August 2005, before making landfall just south of Fort Lauderdale along the southeast coast of Florida on the evening of August 25 as a Category 1 hurricane.

 

Katrina was blamed for 9 deaths in Florida, several as a result of falling trees. After coming ashore, Katrina cut southwestward across southern Florida. The relatively short amount of time the center spent over land combined with the wet marshy composition of the Florida everglades kept Katrina from weakening all that much. As a result, Katrina quickly regained hurricane status after emerging into the Gulf of Mexico, becoming a Category 1 storm on the morning of August 26.

 

Conditions in the Gulf, however, were favorable for development and Katrina began to intensify. By the evening of the August 26, Katrina was a Category 2 storm as it continued to move slowly west-southwest in the southeastern Gulf of Mexico. On the morning of August 27, Katrina became a Category 3 storm with maximum sustained winds reported at 100 knots (115 mph) by the National Hurricane Center (NHC). The central pressure continued to drop throughout the day, however, and the storm began to shift to a more west-northwesterly direction.

 

 

The atmospheric and oceanic conditions favoring hurricane formation make an above-normal season nearly certain (95% to 100%). There is only a 0%-5% chance of a near-normal season, and a 0% chance of a below-normal season. (see Background Information for NOAA’s definitions of above-, near-, and below-normal seasons)

 

An important measure of the total seasonal activity is NOAA’s Accumulated Cyclone Energy (ACE) index, which accounts for the collective intensity and duration of Atlantic tropical storms and hurricanes during a given hurricane season. The ACE index is also used to define above-, near-, and below-normal hurricane seasons. A value of 117% of the median (Median value is 87.5) corresponds to the lower boundary for an above-normal season.

 

For the 2005 Atlantic hurricane season the outlook calls for an extremely active season, with the seasonal ACE index forecasted to range from 180%-270% of the median. This prediction also reflects a continuation of above-normal activity that began in 1995, and will likely be the seventh extremely active season since 1995.

 

Historically, Atlantic hurricane activity has exhibited very strong multi-decadal variability, with alternating periods lasting several decades of generally above-normal or below-normal activity. These multi-decadal fluctuations in hurricane activity result nearly entirely from differences in the number of hurricanes and major hurricanes forming from tropical storms first named in the tropical Atlantic and Caribbean Sea.

 

Hurricane seasons during 1995-2004 have averaged 13.6 tropical storms, 7.8 hurricanes, 3.8 major hurricanes, and with an average ACE index of 159% of the median. NOAA classifies all but two of these ten seasons (El Niño years of 1997 and 2002) as above normal, and six of these years as hyperactive. If the 2005 season verifies as predicted, it will be the seventh hyperactive season in the last 11 years. In contrast, during the preceding 1970-1994 period, hurricane seasons averaged 9 tropical storms, 5 hurricanes, and 1.5 major hurricanes, with an average ACE index of only 75% of the median. NOAA classifies twelve (almost one-half) of these 25 seasons as being below normal, only three as being above normal (1980, 1988, 1988), and none as being hyperactive.

 

"My results suggest that future warming may lead to an upward trend in [hurricanes'] destructive potential, and--taking into account an increasing coastal population--a substantial increase in hurricane-related losses in the 21st century," - Kerry Emanuel professor of meteorology in MIT's Department of Earth, Atmospheric and Planetary Sciences.

[Guest Cheryl Dybas]

Scientists monitoring ocean heat and circulation in the Gulf of Mexico during Hurricanes Katrina and Rita have a new understanding of how these tropical storms can gain intensity so quickly: The Gulf of Mexico's "Loop Current" is likely intensifying hurricanes that pass over eddies of warm water that spin off the main current.

 

"A positive outcome of a hurricane season like this is that we've been able to learn more about the Loop Current and its associated warm-water eddies, which are basically hurricane intensity engines," said Nick Shay, a University of Miami Rosenstiel School of Marine and Atmospheric Science (RSMAS) meteorologist and physical oceanographer.

 

The Loop Current is a horseshoe-shaped feature that flows clockwise, transferring warm subtropical waters from the Caribbean Sea through the Yucatan Straits into the Gulf of Mexico.

 

This year, the Loop Current extended deep into the Gulf of Mexico during hurricane season. Currents at this time of year typically become unsteady and pinch off deep, warm eddies, said Shay. The warm water then becomes ideal for hurricanes in the process of intensifying.