Weather: A storm season to be remembered

Sunday, November 2, 2008

The series of tropical storms that ravaged the Caribbean and the U.S. seaboard this fall caused hundreds of deaths and many billons n damages. Canada wasn't spared, with torrential rainstorms from Windsor to the Atlantic provinces

by HENRY HENGEVELD

After relatively calm seasons in 2006 and 2007, this year Atlantic hurricanes have returned with a vengeance. 

The first four tropical storms of the season passed with relatively little impact on land areas. Hurricane Bertha did reach Category 3 and lasted an unusually long 17 days before it dissipated in the mid Atlantic – unusual for an early season storm. However, the only effect on land areas was a glancing blow to Bermuda in its dying days.

Then, starting in mid-August, the tempo changed. The mayhem began with Tropical Storm Fay. While Fay's wind intensity did not reach the full hurricane status initially predicted by computer models, the rains and tornadoes it unleashed caused 37 fatalities and extensive damage.

Its impact was particularly significant in the Caribbean, severely damaging crops in Haiti, which was already suffering a food shortage. As it migrated northward towards the eastern U.S. seaboard, Fay slowed to a crawl and zigzagged back and forth between coastal ocean waters and the Florida shorelines four times over a period of seven days.

And it rained! Some areas of the state received up to 25 inches (640 millimetres) of rain.  While total costs of property loss due to Faye are not yet known, damages were enough to cause President Bush to call much of Florida a disaster zone. 

As Fay began to fade away over the U.S. interior, the next major storm, called Gustav, was already forming over the tropical Atlantic. Gustav reached hurricane strength on Aug. 26 and reached Category 4 intensity (with winds of 240 km/hr) within three days.    

After passing over several Caribbean islands (again including Haiti), it headed for Louisiana. With memories of Hurricane Katrina in 2005 still fresh in their minds, more than two million people fled New Orleans as it approached. Fortunately, by the time it had reached the Gulf Coast shoreline on August 31, it had weakened substantially.

Still, although large populated regions were spared significant losses, by the time Gustav faded away over the continental United States, it had caused 125 deaths and an estimated $20 billion in damages.   

Hurricane Hanna arrived right on the heels of Gustav. After meandering over several eastern Caribbean islands, it once again hit Haiti hard, dumping heavy rains on an already water soaked terrain. With a very poor population ill-equipped to deal with disasters, the effects were devastating, leaving more than 500 dead and many thousands homeless. Hanna was also responsible for a further seven deaths as it passed through the Caribbean and along the U.S. east coast. 

Even as Hanna began its reign of terror in the Caribbean, Hurricane Ike was already being spawned as a tropical depression off the west coast of Africa. On day three, it exploded from a tropical storm into a Category 4 hurricane within a period of 12 hours. Vacillating between Category 3 and 4 intensity, it quickly passed over the southern Bahamas, Haiti (again!), and Cuba. Some 2.5 million Cubans fled to avoid the brunt of the storm, with many returning to find that their homes had disappeared.

While forecasters had first warned that Hurricane Ike might next make a direct hit on Florida, it had a mind of its own. Instead, it headed westward, out over the Gulf of Mexico and towards the shores of Texas. Its real extent became immense, spanning a distance of 500 miles. One million of the most vulnerable Texans were advised to flee to safety, and oil refineries were shut down as a precaution.

Since these refineries produce approximately 20 per cent of U.S. domestic gas supplies, prices at the pumps across the continent skyrocketed overnight, with prices in Ontario also jumping some 13 cents per litre. Ike crossed the shoreline on Sept. 13 as a Category 2 storm with the eye centred over Galveston and then Houston, ravaging old structures, shattering windows in office towers and causing extensive flooding.

It left more than three million homes and businesses without power, and contributed to 37 deaths. Early estimates suggested total damages were between $8 and $18 billion.  

As I write this, there are still another 10 weeks to go before the 2008 hurricane season is over. Hence, it is very likely that more tropical storms will follow. Some, like Josephine, will fizzle and die without a whimper. Others will likely cause further havoc in at least some parts of the Caribbean and southern United States. While it will take a lot to surpass 2005 in related damages, this will likely be a storm season to be remembered.

Why should Ontarians care? Although these storms' brunt have hit elsewhere, some also affected the weather in Eastern Canada. Hurricane Hanna, for example, degraded into a post-tropical storm which marched northward along the U.S. east coast and into Eastern Canada, sideswiping eastern Ontario. By Sept. 7, Hanna had dropped 141 millimetres of rain in parts of southern New Brunswick, and doused much of the rest of the Atlantic provinces as well.

The remnants of Hurricane Ike, with a more westerly track, headed through the central United States and into southern Ontario. On Sept. 14 and 15, most of southern Ontario received about 25 to 30 mm of rain, with Windsor receiving 96 mm. 

Secondly, while damages from hurricanes tend to fall initially on local insurance companies and emergency relief agencies, through re-insurance programs they also affect our home insurance policies. Don't be surprised by another rate increase.

Finally, while the net impact of climate change on hurricane behaviour is still uncertain and hotly debated, experts agree that – everything else being equal – warmer ocean temperatures increase the energy and water input into tropical storms, and enhance the potential for very intense hurricanes.

While such storms are unlikely to hit Ontario directly, they could send more large rainfall events our way. BF

Henry Hengeveld is Emeritus Associate, Science Assessment and Integration Branch/ACSD/MSC, Environment Canada.