- Experts surveyed by USA TODAY praise the National Hurricane Center’s forecast.
- Ida exploded in intensity before making landfall, going from 85 mph to 150 mph in just 20 hours.
- “Predicting the exact magnitude of a rapid escalation is always a delicate task. “
As Hurricane Ida exploded into a powerful Category 4 storm heading towards the Louisiana coast, it came as no surprise.
Forecasters had predicted the storm’s track for several days – as well as the potential for the system to intensify – and the runway was accurately following the predicted track.
But in New Orleans, Mayor LaToya Cantrell said the storm’s lightning-speed growth has prevented mandatory evacuations in the city. “We don’t have time,” she said on Saturday.
Has Ida’s faster-than-expected growth caught meteorologists off guard?
Experts said no: the accuracy of the National Hurricane Center forecast was perfect and the best possible within the limits of science.
“The NHC was explicitly calling for rapid intensification as soon as the storm formed and had classified Ida as Category 4 approximately 36 hours before landing,” Colorado State University hurricane researcher Phil Klotzbach told USA TODAY .
“Rapid intensification” is a process in which a storm undergoes accelerated growth: the phenomenon is generally defined as a tropical cyclone intensifying by at least 35 mph over a 24 hour period.
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“Rapid intensification occurs when a tropical storm or hurricane encounters an extremely conducive environment,” Klotzbach said. “Typically this environment consists of very hot water, low vertical wind shear, and high levels of average humidity.”
Ida exploded in intensity before making landfall after crossing the unusually warm Gulf waters, going from 85 mph to 150 mph in 20 hours, easily exceeding the official intensification threshold. The storm hit the Louisiana coast on Sunday with winds of 150 mph, making it the fifth strongest hurricane on record in the Americas.
University of Miami hurricane researcher Brian McNoldy praised the forecasts from the earliest predictions. “In the first forecast made for Tropical Depression Nine (Thursday), the NHC made the exceptional appeal to include a rapid intensification in its forecast,” he said.
“This forecast was incredibly confident, and something we hardly ever see,” McNoldy said.
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James Franklin, a part-time contractor at NHC with the Hurricane Forecast Improvement Project, said, “60 hours of time to report a major hurricane landing is admirable.”
Correctly forecasting intensity was an issue he and others had worked on for decades, he said. It looks “pretty good” that the hurricane center was able to say nearly three days in advance that Ida would be a major hurricane upon landing, he said.
“Predicting the exact magnitude of a rapid intensification is always a tricky business,” Klotzbach said. “Ida was in a fairly favorable environment after her passage over the western part of Cuba, but it didn’t really intensify until late Saturday. Then the bottom fell from the storm.”
McNoldy said Ida was a tough decision. “Each subsequent forecast has continued to raise the bar as Ida continued to take full advantage of the ideal environmental conditions in the Gulf,” McNoldy said. “But by the Friday afternoon advisory, (the NHC) the forecast was for a Category 4 hurricane in the northern Gulf, and it stayed correctly in the forecast until the end.”
What role does climate change play in the rapid intensification? Jeff Masters, a former hurricane-chasing meteorologist with the National Oceanic and Atmospheric Administration and founder of Weather Underground, told USA TODAY that global warming is having consequences. “Climate change is causing Atlantic hurricanes to intensify faster, and Ida was one of the 5 fastest-intensity hurricanes on record before a landing in the United States.”
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While scientists expect intensification rates of storms to accelerate with global warming, this may not be easy for forecasters to map. “Given the limitations of hurricane data, it may be some time before we can unequivocally identify this signal in actual observations,” Masters said.
For areas weighing on evacuations, the uncertainty about the exact intensity of the storms could be great. “It takes longer to evacuate a city than it takes to build a destructive hurricane,” said Kelly Hereid, climatologist at Liberty Mutual, tweeted.
Contribution: Dinah Pulver, USA TODAY; The Associated Press