"So far, it's been a record-breaker," said meteorologist Stu Ostro of The Weather Channel. "There was a depression, storm, or hurricane present in the Atlantic, Caribbean, or Gulf of Mexico every day from July 3 to July 29. We've not seen anything like that in July in records going back to 1851."
The five tropical storms that developed in July also set a record, Ostro said. Two of those storms developed into extremely powerful hurricanes. Hurricane Dennis made landfall near Pensacola, Florida, on July 10 with winds of about 120 miles an hour (193 kilometers an hour).
Dennis began as a tropical depression in the eastern Caribbean Sea on July 3 and at one point had winds of 150 miles an hour (241 kilometers an hour).
Hurricane Emily followed almost immediately and achieved winds of 155 miles an hour (245 kilometers and hour), making it the most powerful July hurricane on record. The storm struck Mexico's Yucatán Peninsula with winds exceeding 130 miles an hour (209 kilometers an hour).
Forecasters think the summer of 2005 could surpass the 1933 hurricane season, which was the most active on record. That year, 21 tropical storms formed, creating 10 hurricanes, 5 of which became major hurricanes.
Global Warming or Natural Cycle?
The dramatic increase in tropical storms during the past decade has sparked a widening debate among meteorologists about whether global warming is playing a role in hurricane formation and intensity.
Some researchers say global warming is causing more active hurricane seasons. Others say global warming is not causing more storms to form, but is causing them to become more powerful. See "Is Global Warming Making Hurricanes Worse?"
CSU's Gray and Klotzbach say the stormier summers are part of a well-established cycle of fluctuating hurricane activity. The cycles are caused by ocean currents that alter the salt content of the water, Klotzbach said. When the salt content is higher in the Atlanticas it is nowthe water is warmer, and that causes more tropical storms to form.
When the salt content is lower, the water is cooler and fewer hurricanes form, Klotzbach said.
The cycles take 25 to 40 years to run their courses. The present cycle of increased hurricanes started in 1995 and is expected to continue for at least another decade, perhaps longer.
Klotzbach said that if global warming were affecting hurricane formation, more storms would be forming around the world instead of only in the Atlantic Basin, which includes the Atlantic Ocean, the Caribbean Sea, and the Gulf of Mexico.
"I really can't pick out a trend of increased hurricanes around the world," Klotzbach said. "If you look at the eastern Pacific Ocean, hurricane activity there has gone way down since 1995. There's no trend toward more storms there. It's a tricky problem."
The Weather Channel's Ostro agrees that a natural climate cycle is "playing a significant role" in the recent active hurricane seasons. But other factors also may be at work, he said.
"Global warming might also be playing a role in tropical cyclone activity worldwide, not just in the Atlantic, especially as it relates to hurricane activity," Ostro said.
Still, Ostro noted that determining whether global warming is influencing hurricanes is complicated by the fact that data about hurricanes that formed before 1970 is less reliable than more recent data.
"It's difficult to assess to what extent this climate change is exerting an influence upon the 2004 and 2005 Atlantic hurricane seasons," he said.
Willie Drye is the author of Storm of the Century: The Labor Day Hurricane of 1935, published by National Geographic Books.
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