What was behind the Category 5 upgrade for Hurricane Michael?

By Bryan Norcross - Hurricane Specialist

MIAMI - It’s official!  

When Hurricane Michael came ashore near Panama City, Florida last October 10th, it was a Category 5 hurricane. Only the fourth such storm known to have impacted the continental United States since the mid 19th Century.  

A report just issued by the National Hurricane Center puts the new estimate of Michael’s top sustained winds at landfall at 160 mph. This is just below Hurricane Andrew, which devastated South Miami-Dade County in 1992.  

After every hurricane season, National Hurricane Center forecasters reexamine all of the data that was available when the storm was active to be sure that nothing was missed in the heat of cranking out forecasts and communicating with officials in the affected area.  

In addition, other measurements of wind, pressure, and water height are analyzed that were unknown or unavailable to forecasters while the winds were blowing. Private weather stations, for example, are verified for accuracy after the storm, to fill in gaps in official weather observations across the impact zone.  

In Michael’s case, it was a detailed post-storm analysis of data gathered from sensors dropped from Hurricane Hunter planes and nearby National Weather Service radars that convinced forecasters that the peak winds at about 9,000 feet above the ground were 175 mph or more. That lead to a final estimate of 160 mph as the top wind at the surface of the earth.

Estimate is the key word here. A hurricane’s top winds are almost never measured. Instead they are deduced by scientific analysis of the available data. In the case of Michael, some of the science is still developing, which might eventually lead to a further slight adjustment of the 160 mph estimate in the future.

Slight changes to the official record of landfalling storms are quite common, though Michael’s upgrade will receive more notice than usual because it crosses the line into rare Category 5 territory.

People in and around Panama City are no doubt pleased by the news. It raises the profile of the horrendous event they experienced, and the aftermath they are continuing to endure. Hopefully, it will refocus attention on the ongoing challenges that Panama City and the surrounding area face, and will face for years to come.  

The new report details the accuracy of the National Hurricane Center’s forecasts, both in terms of the track the storm took, and how strong it was. The track forecasts were excellent – better than average. The intensity forecasts were poor, however. Michael intensified quicker, and got significantly stronger than forecast.  

The best computer models did not pick up on Michael’s rapid intensification, which continued up to landfall. It’s the steady improvement in those models that has allowed the Hurricane Center to make better and better forecasts. But Michael is a reminder that while the average errors are decreasing, significant outliers can still occur.

There will be a tendency for some folks to claim they would have been better prepared if only they had known a Category 5 hurricane were bearing down. Unfortunately, that’s likely true. Category 5 hurricanes scare people to a higher pitch than a mere Category 3. This is a dangerous conception that needs to be eradicated.

More than a day in advance, the official forecast was for a high-end Category 3 hurricane at landfall. Anyone who took this forecast as anything but dire misanalyzed or ignored the extreme threat. If Michael had arrived as a 125 mph Category 3, the damage would still have been extreme.

In any case, the Category 5 winds were likely confined to a very small area offshore and right near the coast in or near the Mexico Beach area, where the storm surge destroyed almost every home. Most of the Panama City area experienced lesser winds, which is the real lesson of Michael.  

While it feels better that so much damage and disruption was caused by a Category 5 hurricane, the fact that buildings in the eastern Florida panhandle were intentionally built to a lesser standard than the rest of the state cannot be forgotten.  

Category 5 hurricanes are always going to inflict significant damage right where the worst of the storm hits. But that doesn’t mean that areas that get hit by Category 1, 2, or 3 winds, which is what happens in most of the impact zone, need to be demolished as well. Residents must have confidence that homes and buildings in their city are built to standards appropriate to the natural threat. In Florida, that means they have to be ready for strong hurricanes.

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