Hurricane Rita in the Gulf of Mexico in September 2005. Aircraft flown into Rita and other hurricanes have offered new insights into how massive storms suddenly gain and lose strength.

Credit: NASA

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WASHINGTON: Flying research aircraft into the intense hurricanes of 2005 has offered new insights into how the massive storms suddenly gain and lose strength, U.S. scientists say.

The new understanding could allow meteorologists to accurately forecast changes in the power of hurricanes, just as they now predict their directions, according to Robert Houze, a professor of atmospheric sciences at the University of Washington in Seattle.

A team of researchers led by Houze collected data inside the centre of deadly hurricane Rita and other storms of 2005 - the heaviest hurricane season ever. Their results showed that the eyewall - the violent wall around the still eye - can be interrupted and destroyed by an outer ring of dry air, or a 'moat' that develops as the hurricane eye tightens and the storm intensifies.

In a summary of their research, which was published this week in the U.S. journal Science, Houze and his associates said they observed how the moat can form around the eyewall, where the storm's winds reach their highest speeds.

The moat takes shape as outer rings of clouds spin into a second external eyewall. Together the two formations then subsume the original eyewall, effectively widening the storm and slowing its spin, at least temporarily, according to the scientists.

As the new eyewall takes shape, though, the storm can re-intensify.

"The exciting thing about the data from Rita is that they show that the moat is a very dynamic region that cuts off the old eye and establishes a wider eye," Houze said. "It's not just a passive region that's caught in between two eyewalls."

Houze's team used data from aircraft flown by the U.S. Navy and the National Oceanic and Atmospheric Administration into the massive hurricanes of 2005, which included the deadly Katrina and Rita and the most intense Atlantic storm on record, Wilma.

Rita, which grew in less than 24 hours from a weak category one hurricane to the strongest category five, provided a view into how the intensification and slowing processes took place.

Data was fed into a computer model at the University of Miami's Rosenstiel School of Marine and Atmospheric Science in Florida, where Houze's co-researcher Shuyi Chen said it was able to accurately model storm changes.

"The model provided an exceptionally accurate forecast of eyewall replacement, which was key to guiding the aircraft to collect the radar data," Chen said.

"The comparison between Katrina and Rita will be interesting because we got excellent data from both storms. Rita was the one that showed the eyewall replacement," said Houze.