Tim G
Well-Known Member
HURRICANE FRANCES -- CLOSING IN
Factors may stop storm from regrowth
The hurricane is hurt by wind shear and its proximity to land.
September 4, 2004
A weaker Hurricane Frances crept closer to Central Florida on Friday under conditions that appeared unfavorable for the storm to regain its former strength.
The mammoth storm lost some of its punch as it pounded the Bahamas, becoming a Category 2 storm Friday evening, with sustained winds near 105 mph.
Experts said there were signs Frances could continue weakening before landfall, but forecasters at the National Hurricane Center outside Miami cautioned that intensity predictions are, at best, an inexact science.
"We really don't have good skills on intensity yet," said Lixion Avila, a hurricane-center forecaster. "Will Frances get weaker? Will it get back to Category 4 [with winds greater than 130 mph]? We just don't know."
A number of factors could prevent the storm from getting stronger.
One is the easterly wind flow generated by a high-altitude area of low pressure off the coast of Jacksonville. Those upper-level winds are shearing the top off the hurricane, providing some resistance to the storm's regaining its intensity.
Another obstacle is Frances' massive size. Hurricanes build over the ocean as they suck in warm, humid air and expel drier, cooler air into the upper atmosphere. This giant heat engine -- an average hurricane produces energy comparable to the United States' total annual output of electricity -- is throttled back when storms move over land.
Frances' passage through the Bahamas on Friday was a factor in the storm's getting weaker and less organized but slightly more spread out.
By the time of the hurricane's predicted landfall today on Florida's Atlantic coast, much of the storm will be over land. That cuts down on the fuel available for Frances to grow stronger.
"The intensity should start dropping 12 hours before landfall," said T.N. Krishnamurti, a professor of meteorology at Florida State University. "This storm is so big that half of the storm will be over land, not receiving energy from the ocean, before the eye ever makes landfall."
The inner wall surrounding the storm's eye became weaker and less well-defined Friday before a new eye wall began appearing to take shape. Meteorologists say the phenomenon is normal with many hurricanes and isn't necessarily a predictor of the storm's eventual strength.
"As this transformation begins, the storm can weaken or wobble some," Krishnamurti said. "But then a new inner eye wall can form up again."
One factor in Frances' favor is that the storm's path soon will bring it into shallower, warmer waters off Florida's East Coast. The so-called Gulf Stream effect often makes storms more intense.
In this case, however, the effect is expected to be marginal. The Gulf Stream's 87-degree water temperatures are only a degree or so warmer than those in the storm's present location.
Forecaster Avila expects the intensifying effects of the Gulf Stream and inhibiting influence of the upper-level winds to more or less cancel each other out.
"I think the best bet at the moment is for the storm to remain at close to its current intensity," Avila said.
Krishnamurti is more optimistic, predicting Frances could weaken to a strong Category 1 storm with winds less than 96 mph.
Experts agree that regardless of wind speed, the slow-moving hurricane will deluge Central Florida with torrential rain, perhaps as much as 18 inches in some locations. And floodwaters often are the deadliest part of the storm.
"Don't let your guard down," said Max Mayfield, director of the National Hurricane Center. "Just because we don't have that distinct eye doesn't mean this isn't a powerful storm. It has a very wide wind field capable of causing enormous damage and, if we're not careful, loss of life."
Factors may stop storm from regrowth
The hurricane is hurt by wind shear and its proximity to land.
September 4, 2004
A weaker Hurricane Frances crept closer to Central Florida on Friday under conditions that appeared unfavorable for the storm to regain its former strength.
The mammoth storm lost some of its punch as it pounded the Bahamas, becoming a Category 2 storm Friday evening, with sustained winds near 105 mph.
Experts said there were signs Frances could continue weakening before landfall, but forecasters at the National Hurricane Center outside Miami cautioned that intensity predictions are, at best, an inexact science.
"We really don't have good skills on intensity yet," said Lixion Avila, a hurricane-center forecaster. "Will Frances get weaker? Will it get back to Category 4 [with winds greater than 130 mph]? We just don't know."
A number of factors could prevent the storm from getting stronger.
One is the easterly wind flow generated by a high-altitude area of low pressure off the coast of Jacksonville. Those upper-level winds are shearing the top off the hurricane, providing some resistance to the storm's regaining its intensity.
Another obstacle is Frances' massive size. Hurricanes build over the ocean as they suck in warm, humid air and expel drier, cooler air into the upper atmosphere. This giant heat engine -- an average hurricane produces energy comparable to the United States' total annual output of electricity -- is throttled back when storms move over land.
Frances' passage through the Bahamas on Friday was a factor in the storm's getting weaker and less organized but slightly more spread out.
By the time of the hurricane's predicted landfall today on Florida's Atlantic coast, much of the storm will be over land. That cuts down on the fuel available for Frances to grow stronger.
"The intensity should start dropping 12 hours before landfall," said T.N. Krishnamurti, a professor of meteorology at Florida State University. "This storm is so big that half of the storm will be over land, not receiving energy from the ocean, before the eye ever makes landfall."
The inner wall surrounding the storm's eye became weaker and less well-defined Friday before a new eye wall began appearing to take shape. Meteorologists say the phenomenon is normal with many hurricanes and isn't necessarily a predictor of the storm's eventual strength.
"As this transformation begins, the storm can weaken or wobble some," Krishnamurti said. "But then a new inner eye wall can form up again."
One factor in Frances' favor is that the storm's path soon will bring it into shallower, warmer waters off Florida's East Coast. The so-called Gulf Stream effect often makes storms more intense.
In this case, however, the effect is expected to be marginal. The Gulf Stream's 87-degree water temperatures are only a degree or so warmer than those in the storm's present location.
Forecaster Avila expects the intensifying effects of the Gulf Stream and inhibiting influence of the upper-level winds to more or less cancel each other out.
"I think the best bet at the moment is for the storm to remain at close to its current intensity," Avila said.
Krishnamurti is more optimistic, predicting Frances could weaken to a strong Category 1 storm with winds less than 96 mph.
Experts agree that regardless of wind speed, the slow-moving hurricane will deluge Central Florida with torrential rain, perhaps as much as 18 inches in some locations. And floodwaters often are the deadliest part of the storm.
"Don't let your guard down," said Max Mayfield, director of the National Hurricane Center. "Just because we don't have that distinct eye doesn't mean this isn't a powerful storm. It has a very wide wind field capable of causing enormous damage and, if we're not careful, loss of life."