Satellite image of Hurricane Katrina, the costliest natural disaster in U.S. history. (Courtesy of NOAA)
In Depth
Forces of nature
Summer weather: more than a conversation starter
June 6, 2007
By Sabrina Saccoccio, CBC News
No longer just something to talk about, the weather seems to be a cause for real concern — especially when U.S. experts are predicting seven to 10 hurricanes between now and the end of November.
The Atlantic hurricane season, which began last week and ends Nov. 30, will likely be a severe one, according to the U.S. National Oceanic and Atmospheric Administration (NOAA).
Three to five of the predicted hurricanes are estimated to be comparable to or even more unrelenting than hurricane Katrina, one of the most devastating U.S. natural disasters.
Colorado State University scientists have predicted nine hurricanes ranked at a minimum of Category 3 (like Katrina), and a 74 per cent chance the United States will endure one major hurricane.
"For 2007, we're predicting a high probability of an above-normal Atlantic hurricane season," explained NOAA forecaster Dr. Gerry Bell. "We're in an active hurricane era that started in 1995, and while we can't say for sure how long this era will last, historically other eras have lasted 25 to 40 years."
Each year, NOAA forecasts storms severe enough to be "named" — as with Andrea, a subtropical cyclone that developed before hurricane season on May 9 and was the first pre-season storm since 2003.
This year, the outlook is 13 to 17 named storms.
A normal hurricane season is generally predicted to have 11 named storms, with six becoming hurricanes, and two of those being major.
Canadian correlations
Canadian experts don't make official hurricane season predictions.
"But we do interpret the ones that are issued from the States — and they're calling for quite an active season," confirmed Bob Robichaud, an Environment Canada Hurricane Centre meteorologist.
Robichaud said it's difficult to correlate the American predictions with Canada's weather.
Not even NOAA tracks where the storms may end up. But what Canadians can count on is the entire country won't be blasted by hurricanes.
"They don't travel that far inland. Really, you're just looking at Atlantic Canada. Once these storms get into Quebec and Ontario they transform into a regular extra tropical system," he explained.
People most at risk for damage tend to be on the coast. NOAA urges residents on the eastern and Gulf shorelines, and those in the Caribbean, to predetermine a hurricane plan, since studies have shown people who are prepared suffer less. The possible severity of a storm is also important to consider.
Extensive research out of NOAA's Washington, D.C., office has found hurricane landfalls are sharply increasing. Rather than just stabilizing over bodies of water, the storms are more often touching down on land.
Prediction accuracy
A sceptic might figure you can't bank on weather predictions. Like last year, when NOAA called for a busy hurricane season but it didn't happen. Does this mean predictions are inaccurate?
Not exactly.
Each year, the organization issues a hurricane outlook in May, and then updates it in August prior to peak season; the storms tend to hit mostly in August, September and October.
Since 1998, when NOAA started issuing forecasts, only last year's predictions were nearly unreliable. But that was because of an unexpected mitigating factor — an El Nino.
Hurricanes developing in the Atlantic Ocean, Caribbean Sea or the Gulf of Mexico require warm water to drive them. They also need an unstable atmosphere. Last year, waters were warmer but El Nino stabilized the atmosphere to the point where expected hurricane activity was cancelled out. Instead, storms were steered by currents that kept them mostly over open water, and not on land.
Likely in a La Nina
El Nino has since passed but forecasters detect evidence of the system's evil twin sister La Nina.
Maps are showing La Nina conditions of cooler-than-normal Pacific water temperatures. Since February, chilly waters have been detected off the coast of Peru.
While an El Nino mediates hurricanes, being in a La Nina cycle has close to no effect on how they develop — meaning NOAA's predictions might be back on track.
Cooler Pacific waters, coupled with the current Atlantic temperatures measuring at about one degree above normal, make for perfect storm conditions.
"It's the warm waters of the Atlantic that cause the hurricanes and the cold water in the Pacific that lets them thrive," Robichaud explained.
La Nina is a historic weather phenomenon that occurs in the Pacific Ocean's atmosphere. Its effects are mostly opposite to El Nino's hotter, drier conditions.
La Nina tends to produce colder episodes and places like Australia, suffering drought during El Nino, become damper than normal.
In North America, La Nina's effects are felt in the winter and are likely to be mixed. Winters are colder and wetter in the northwest, but warmer in southeastern areas.
La Nina reoccurs every few years and can last up to two years each time.
A cause for concern or just more talk?
Tracking weather has become more prevalent these days, with the Weather Network — as well as other channels and websites, which offer morning-to-night daily forecasts — perpetually answering the question: Do I need an umbrella?
It's clear that they've helped make weather an even more prominent subject for conversation. These days, if people seem to know more about the weather, it's because meteorologists generally do.
These experts employ state-of-the-art supercomputers and satellites to predict storms. But as Robichaud explains, weather satellite use was only perfected in the 1980s.
That leaves 20 years of data to compare today's weather with, implying patterns might not be getting any worse.
The jury's still out on if more hurricanes and climate change are related. Some meteorologists have spent their entire careers trying to decipher a connection. Now, some have even estimated that climate change might lower hurricane rates (climate change tends to stabilize the atmosphere).
So is there cause for concern?
Robichaud said: "We may not actually have more storms now than we did in the past. We're just better at seeing them."
