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A mild winter and prevailing southerly winds are the likely reasons water temperatures are above normal in a million square kilometres of ocean. ((Government of Canada))

A huge section of the Atlantic Ocean offthe East Coastis much warmer than normal, and that has weather forecasters nervous as hurricane season gets underway.

"I haven't seen a warm water anomaly quite as big as this in a while," Chris Fogerty, with the Canadian Hurricane Centre, told CBC News.

Recent readings showedtemperatures were two to five degrees above normal in a million square kilometres of ocean stretching from off the coast of Maine to the Grand Banks off Newfoundland.

Hurricanes tend to lose power as they pass over cooler water. But if the water is a few degrees above normal, Fogerty said it will increase a storm's capacity to cause damage.

"We could see storms having a little more energy a little bit longer," he said.

Fogerty points to the example of hurricane Juan, which moved over waters three to four degrees above normal before smashing north through Nova Scotia and on to Prince Edward Island in 2003.

"The fact the water was warmer than normal actually increased the damage by, we estimate, 30 to maybe as much as 50 per cent," he said.

Mild winter, warm winds

Fogerty blames the mild winter and prevailing southerly winds for the rise in water temperature.

There was less ice coverage this year, he said, "so the ice melted earlier and the water almost had a head start."

Environment Canada is warning residents to prepare for another active hurricane season, though no one is predicting a deadly storm like Juan.

Still, Ernie Fage, Nova Scotia's minister of emergency preparedness, says residents should pay attention to weather warnings.

"I think it's incumbent on all of us to watch closely and be prepared, and we are attempting to do that," Fage said.

Season will be active, but not like last year

A meteorologist with the national weather service headquarters in the U.S. says this year will be an active hurricane season but not as severe as 2005.

Dennis Feltgen, who is based in Maryland, told CBC News that while waters are warmer than usual off northeastern North America, they are still cool enough to slow down a storm.

"It isn't so much that it's warmer than normal, it is also how much the temperature actually is," said Feltgen.

"For instance, if it's 60-degree-Fahrenheit water and it's now 65-degree water, that's still below 80 degrees."

Feltgen said forecasters in the U.S. are predicting four Category 3 hurricanes this year. Hurricane Juan was Category 2 when it struck Nova Scotia.

There is no way to currently predict if any hurricanes will strike Atlantic Canada this year, said Feltgen. That kind of prediction can only be made on individual storms once they have formed.