All across the country, extreme weather events seem to be making the headlines on a regular basis. What's going on? Has the atmosphere suddenly gone wacky? Is global warming to blame? What about El Niño or La Niña? Are all of these extreme weather events simply the result of natural variations in the Earth's ever changing climate? And is there anything you can do about it?

Even though these extreme weather events may seem random, there are global circulation patterns both in the atmosphere and in the oceans that can help meteorologists predict whether certain parts of the U.S. may be affected by bitter cold and snow in the winter, or deadly hurricanes during the summer and fall. Accurate forecasts can help you plan to protect your organization from the oldest, and perhaps greatest, threat of all-Mother Nature.

If You Build It …

Of all the extreme weather events observed in recent years, the most damaging in terms of cost as well as in lives lost have been hurricanes. Hurricanes represent the single greatest weather risk from Texas through Virginia. Residual heavy rain from decaying tropical systems can extend well inland into the Tennessee and Ohio valleys. While the damage from most extreme weather events-snow storms, tornado outbreaks, floods, wildfires- can be measured in millions of dollars, a single major hurricane impact can result in between $15 and $40 billion in damage if a major population center is affected. Over the last 30 to 40 years, there has been a significant population increase along the Gulf Coast and along the East Coast of the US. For example, in 1969 Hurricane Camille-arguably the strongest hurricane ever to strike the U.S. coast- made landfall in southwest Mississippi with sustained wind near 180 miles per hour and gusts to well over 200 miles per hour. Camille pushed a wall of water over 25 feet high inland for miles along the Mississippi coast. Almost every structure along the Mississippi coast was severely damaged or destroyed completely and damage  exceeded $1.4 billion. But back then, the Mississippi coast consisted of a few hotels, many old warehouses, and some fishing piers. Today, the Mississippi coast is lined with large casinos and extravagant hotels, some worth billions of dollars. If a hurricane the strength of Camille were to strike the same area today, the cost would be magnitudes higher. In 1992, a much smaller but almost equally powerful hurricane struck just south of Miami, generating over $25 billion in damage. Fortunately, Andrew's strongest winds passed south of the highly populated Miami area or the monetary cost could have easily doubled to $50 billion or more.

Change Is in the Air

Back in the 1940s to1960s, when a large number of major hurricanes made landfall, there wasn't as much property to destroy as there is now. Because no other weather event comes close to causing as much death and destruction over a large area as a major hurricane, it is unsettling that there are strong  signals that the 2004 hurricane season may not be an anomaly. Weather patterns across the northern hemisphere may indeed be changing. Remember the large number of Costly and deadly hurricane landfalls and the unusually cold winters from the 1940s through the 1970s? In the severe winter of 1976, the Mississippi River froze from Minnesota southward almost to St. Louis and ice was reported all the way south to New Orleans. There is quite a bit of talk about global warming these days, but does anyone remember the dire warnings of global cooling back in the 1970s? At that time, scientists were convinced that the Earth would soon be plunging into a mini Ice Age-books were written on the subject. Then came the warm decades of the 1980s and 1990s and talk of another Ice Age faded.

In most cases, "normal" weather is really an average of extremes. The extreme hurricane season of 2004 may be a harbinger of real change. Recent evidence suggests that a pattern change that began in 1995 is now in full swing across North America. The key to future weather across North America lies in the Atlantic and Pacific Oceans. The oceans play a vital role in weather patterns around the world. As major sources of heat and energy, the oceans affect the atmosphere from top to bottom. In the mid 1990s, researchers made an amazing discovery while studying ice core samples in Greenland. They found strong evidence of a regular cycle of temperature variations in the Atlantic Ocean going back thousands of years. Over periods ranging 20 to 50 years, the Atlantic sea surface temperatures (SSTs) went from about 0.5 degrees Celsius below normal to 1 degree Celsius above normal. These oceanic temperature cycles have been in place for many thousands of years, so it's unlikely that global warming is having any impact. Although many scientists agree that there is evidence to support the idea that the Earth may have warmed slightly in the past 100 years, there is little evidence to suggest that such change is the result of anything other than longer-term natural climatic variations. Additionally, there appears to be no evidence at all to support the theory that any global warming has had any significant impact on any recent storminess across the U.S., tropical or otherwise. Again, remember the warnings of global cooling back in the 1970s. Such fluctuations in climate appear to be normal. The reason for the subtle changes in SSTs across the Atlantic has to do with a large- scale circulation pattern in the Atlantic Ocean called the Atlantic thermohaline circulation or, more simply, the conveyor belt. The basic circulation in the North Atlantic drives water northward from near the South Polar region, across the Equator to approximately 50 to 60 degrees north latitude, where it sinks and returns to the South Polar region. Salinity changes, primarily in the North Atlantic, can impact the general circulation speed of this conveyor belt. Because saltier water is denser than fresh water, when the North Atlantic is saltier, the speed of the conveyor belt increases. The increased speed of the current brings warm surface water much farther to the north.

Over a period of decades, the  warmer water at farther north latitudes results in increased storminess and rainfall. Even- tually, the salinity of the Atlantic declines and the conveyor belt slows down. This process takes about 30 to 50 years, on average. A similar circulation pattern exists in the Pacific Ocean. Cold water in the deep ocean travels northward across the Equator where it slowly warms, rises to the surface, then moves southward back to the Equatorial regions. The regular multidecadal fluctuations of sea surface temperatures in the eastern Pacific is known as the Pacific Decadal Oscillation, or PDO. It has long been known that our climate undergoes regular multidecadal variations. These variations are brought on, at least in part, by the cyclical temperature variations of the Atlantic and Pacific Oceans discussed earlier. Basically, ocean surface temperatures can directly affect the mean positions of subtropical high-pressure and low-pressure areas. A warmer North Atlantic allows the Azores-Bermuda high-pressure center to build farther westward toward the U.S. In 1995, the Atlantic Ocean began heating up after 25 years of below- normal temperatures. Climatology suggests that the North Atlantic SSTs will likely remain above normal for at least another two to three decades. Two years ago, the eastern Pacific Ocean entered what appears to be a multi decadal pattern of below-normal temperatures.

Such a combination of a warmer than normal North Atlantic and a cooler eastern Pacific has not been observed since the 1940s through the 1960s. If we look back at the weather of that period, we can get a glimpse of what we might expect over the coming decades. The middle part of the last century was a very stormy period for the U.S. from the Rockies eastward. With the eastern Pacific cooler than normal, there were fewer episodes of El Niño, the warming of the equatorial waters off the coast of South America. Fewer El Niños meant that the weather along the west U.S. coast was a little less stormy than normal during the winter months.

But just the reverse was true across the rest of the country. Bitterly cold Arctic air invaded the U.S. on a regular basis from the 1940s through the 1960s and even into the mid 1970s. It was a period of increased snowfall along the U.S. East Coast. More significantly, the warmer North Atlantic became a breeding ground for very powerful hurricanes. During the 25 year period from 1944 to 1969, 83 major Category 3, 4, or 5 hurricanes developed in the Atlantic Basin, as compared to only 38 major hurricanes during a similar 25 year period when the North Atlantic SSTs were cooler than normal from 1900 to 1926 and again from 1970 to 1994. Hurricanes are basically heat engines. The warmer the underlying water, the stronger they can become. Climatology tells us that when the North Atlantic enters its warm phase, as it did in 1995, more hurricanes reach major hurricane intensity of 115 miles per hour sustained winds or greater. In fact, in the past 10 years (since the North Atlantic began heating up), we have witnessed the development of 38 major hurricanes- more major hurricanes than in any other 10-year period in recorded history. 

Generally, about  a third of all major hurricanes should be  expected to make landfall somewhere along the U.S. coast. That was true from 1944 to 1969, when of the 83 major hurricanes, 23 struck the U.S. However, until the 2004 hurricane season, only three of the 32 major hurricanes that developed from 1995 to 2003 reached the U.S. coast. Note that very few major hurricanes impacted Florida and the southeast U.S. coast when the Atlantic was cooler from 1970 to 1994. Now compare with Figures 4a and 4b, which represent a similar 25-year period when the Atlantic was warmer than normal. Quite a difference!

The Forecast?

So warmer water in the Atlantic does appear to increase the number of major hurricanes. If that's true, and the Atlantic is beginning to heat up now, then what does the future hold for the U.S.? It's the recent change in the eastern Pacific that may be responsible for the increased major hurricane landfalls along the U.S. coast during the 2004 hurricane season. As was the case from the 1940s through the1960s, the combination of a cool eastern North Pacific and a warm western North Atlantic has changed the basic steering currents of hurricanes. Most of the major hurricanes that developed between 1995 and 2003 turned northward and out to sea before reaching the U.S. coast. But 2004 marked the beginning of a new regime, with a stronger-than-normal Azores-Bermuda high-pressure area in the North Atlantic during the summer months driving more hurricanes farther westward before they were allowed to turn to the north. Such a pattern of increased major hurricane landfalls along the U.S. coast will very likely continue over the next two to decades. Instead of one major hurricane landfall every five to six years, the U.S. may experience a major hurricane landfall every two to three years. Consider a few possible scenarios, which could well occur during the next few decades.

New Orleans

New Orleans is a disaster waiting to happen. The entire city is sinking. The only reason that New Orleans is not under water now is because of a series of levees surrounding the city. Huge pumps are needed to remove rainwater from the city. It's been estimated that if/when a major hurricane makes landfall south of New Orleans that the storm surge could top the levees and the whole city could be under 15 to 30 feet of water. And because New Orleans lies about 10 to 15 feet below sea level, the water could remain for months until the levees are rebuilt, the pumps replaced, and the water pumped out. Before the city could be inhabited again, each and every structure would have to be inspected for safety. Consider the cost involved to rebuild a city the size of New Orleans. Where would more than a million people live while the city was uninhabitable? Even more disturbing, recent studies suggest that only about 60 percent of the approximately 500,000 people living in New Orleans would evacuate before the hurricane hit, leaving an estimated 200,000 people to weather the storm. Of those, as many as 80,000 would likely drown as the city fills with water. Such a disaster was only narrowly averted in 2004 as powerful Hurricane Ivan veered to the east at the last hour, sparing the city of New Orleans.

Houston-Galveston

The Houston-Galveston area is home to a large number of petrochemical refineries, responsible for producing much of the gasoline used across the U.S. A direct hit-which has happened about eight times in the past 100 years-could shut down many if not most of the petrochemical refineries in the region, perhaps for months.  Such a disruption would result in dramatic price increases in fuel prices across the country, not to mention the high cost of rebuilding homes and businesses in the Houston-Galveston area. It's been 22 years since the Houston-Galveston area was affected by a major hurricane, and Alicia was just barely a major hurricane. Prior to 1983, the region was struck by a major Category 3, 4, or 5 hurricane about once every 10 years. Time is short before the next major impact here. It could well happen in 2005.

Long Island

Long Island, NY is not immune to the wrath of hurricanes. Although it's rare for major hurricanes to reach such far northern latitudes, it can happen. The Great 1938 New England Hurricane slammed into Long Island at a speed of over 60 miles per hour, putting much of the island underwater. Most of the people did not even realize that a hurricane was upon them, even as the waters began flooding their coastal homes. The hurricane produced tides of 15 to 18 feet across most of the Long Island and Connecticut coasts, and 18- to 25- foot tides from New London east to Cape Cod. The destructive power of the storm surge was felt throughout the coastal community. Downtown Providence, RI was submerged under a storm tide of nearly 20 feet. Although not as likely as the previous two scenarios, another major hurricane landfall on Long Island today would be extremely costly, both in terms of dollars and lives. And such a landfall is entirely possible given the current and projected weather patterns across the Northern Hemisphere. Have a business continuity plan and keep it up to date. If you're located within 100 miles of the coast in a hurricane-prone area, you should be prepared to have no electricity for one to two weeks, and sometimes longer, after a hurricane hits. Can your business survive such an interruption? Hire an engineering consultant to evaluate your facility's exposure to potential wind damage from hurricanes and other storms that could produce strong winds. Consider relocating vital operations centers away from "risky" weather areas. Areas within 100 miles of the coast from South Texas through Maine would qualify as risky areas. Hurricanes would be the main threat from Texas through Virginia, while major winter nor'easters would be more of a threat farther north up the East Coast. The state of Florida is probably the riskiest part of the U.S., weather-wise, as we saw in 2004. The combination of flat terrain and narrow peninsula offer little protection for a hurricane's extreme wind and storm surge. The National Weather Service and National Hurricane Center perform an excellent service as far as warning the general public of approaching storms. But a private weather provider can fill in the gaps, working closely with you before, during, and after a major storm, allowing you to better assess potential risks so that you can make those critical decisions with the best information possible.

Storm of the Century

Another Storm of the Century may be looming in the not- too-distant future. On March 10, 1993, the relatively primitive computer models of the time indicated that a quite extraordinary storm would be developing in the Gulf of Mexico over the next 48 to 72 hours. Forecasters had never before seen such a storm predicted by computer models. Some were reluctant to believe it could even happen. As the Polar jet stream raced southward out of Canada across the central and eastern U.S., cold Arctic air had spilled southward into the central and eastern Gulf of Mexico. Simultaneously, a secondary jet stream across the southern U.S. fed a considerable amount of energy into the Gulf. The collision resulted in the development of a storm of historic proportions, which came to be known as The Storm of the Century. It was larger than most hurricanes, with winds of 75 to 120 miles per hour. Ahead of the storm was a line of severe thunderstorms that slammed into the western Peninsula of Florida, producing wind gusts to 100 to 120 miles per hour. The storm tracked to the northeast, across northern Florida and up the East Coast, strengthening along the way. To the west and northwest of the storm track was a band of snow 40 to 60 inches deep. Heavy snow fell as far south as the Florida Panhandle. Another such storm is not as farfetched as one might think. Weather patterns across the U.S. in February and March of 2005 were very similar to the pattern that was in place in February of 1993 prior to the development of the March 1993 storm. The scenarios above are not science fiction. A few have a very good chance of coming true over the next few decades. It's safeto say that the most dangerous place to live and work  weather-wise in the next 20 to 30 year would be along the Gulf Coast and from the east coast of Florida northward to New York. Florida and the Southeast U.S. states would be at the greatest risk of being hit by a major hurricane in the  decades to come.

Secondarily, we expect more storminess across the Ohio Valley and along the U.S. East Coast in the coming decades. There will be more cold air outbreaks and more snowstorms. Snow will occasionally dip down to the Gulf Coast, as it did on Christmas Eve of last year 2004. The next Storm of the Century may not be too far off in the future. The U.S. West Coast and the U.S. Southwest will tend to be less stormy in general, as the strong El Niños of the 1970s through the early 1990s are replaced by more and stronger La Niñas. Just think back to the 1940s through the 1960s and you'll have a good idea what to expect in the decades to come. That retirement home in Florida or on the Outer Banks of the Carolinas may not be such a good idea, after all. One thing is certain: the United States will continue to experience extreme weather events for the foreseeable future.

As a Louisiana native, Chris Hebert is no stranger to stormy weather. With a degree in meteorology, Hebert worked for Universal Weather and Aviation, Inc. (Houston, TX) before joining ImpactWeather, a division of Universal Weather, as supervisor and lead hurricane forecaster. Hebert manages ImpactWeather's Storm Team, a group of meteorologists who predict the paths and effects of major winter storms, large-scale severe weather events, and hurricanes. He can be reached at (877) 792-3220.