Hurricane Michael: why it’s so hard to predict storm intensity

Early this week, the National Hurricane Center issued a five-day forecast showing Hurricane Michael making landfall near Mexico Beach, Florida. It predicted that the storm would arrive with 80 mph winds.

Yet the storm that arrived Wednesday was not like the one predicted. It was an extremely intense Category 4 storm with 155 mph winds. Measured by barometric pressure, Michael was one of the top four most powerful storms to ever make landfall in the US. When it came ashore, meteorologists say, it was like a 20-mile-wide tornado.

Mexico Beach, Florida, has nearly been flattened. Uncounted homes in the Florida Panhandle are destroyed, and at least two people died Wednesday as the storm, still a hurricane, continued on into Georgia. Brock Long, administrator of the Federal Emergency Management Agency, told CBS that rescue crews are still struggling to get into Mexico Beach, Apalachicola, and Panama City Beach, and that he fears the death toll will rise.

All told, Michael revealed how impressive hurricane forecasting has become but just how uncertain it still can be. By knowing where a storm will hit many days in advance, evacuations can begin. But it’s still frustrating that the intensity of a storm like Michael can quickly shift for the worse (or better), with an uncomfortable amount of uncertainty.

In terms of Michael’s path, the forecast was remarkably accurate, with the storm landing just about where the NHC predicted it would at the beginning of the week. In the following GIF, watch the storm track forecast evolve over the week. The bulls-eye target of the storm on the Florida Panhandle doesn’t change much.

National Hurricane Center

Predicting intensity harder because there are so many factors that go into hurricanes: ocean temperatures; changes in wind direction higher up in the atmosphere, known as wind shear; and interactions with land. Atmospheric scientists don’t yet have the density of data or the computer models to make huge improvements in this area.

You can see the biggest difference in the following charts. Here’s a chart showing improvements in forecast track. Something to notice: In 2017, the NHC’s predictions 72 hours in advance of a storm were more accurate than its predictions 24 hours in advance of a storm in 1990. That’s an incredible improvement that helps communities prepare and saves lives.

National Hurricane Center

Improvements in computer models, computer processors, and data collection (obtained via actually flying planes through hurricanes) all contribute to this great increase in predictive power.

Consider what happened with Hurricane Irma last year.

That storm skirted through the Caribbean and then took a nearly 90-degree turn northward toward Florida. The NHC predicted this northward turn would happen four days out. There was some uncertainty if the storm was going to impact the Gulf Coast or the Atlantic Coast. “But the fact it was known a few days in advance that the storm was likely to do that was an incredible feat of tech and science,” Rebecca Morss, a scientist at the National Center for Atmospheric Research, said in an interview last year.

National Hurricane Center

And now look at this chart forecast intensity improvements. The trend is much flatter, and noisier.

National Hurricane Center

There are some reasons why Michael became so intense, so quickly, as the Verge explained. Michael was at first in a weakened state due to wind shear, and then entered some really hot Gulf waters with less shear. “The thing was going to just explode,” University of Georgia atmospheric scientist Marshall Shepherd told the Verge.

Michael “did intensify faster and deeper than most models predicted, but we knew it was going to ramp up over the Gulf,” Jeff Weber, a meteorologist with the National Center for Atmospheric Research, told Vox. It was “slightly unexpected to get that intense, but no surprise.”

Overall, the trend of increasingly accurate forecasts is likely to continue. NOAA has launched two new satellites monitoring into our atmosphere this year. And it continues to update its computer models to make forecasts.

But here’s the bigger lesson: If you see a hurricane track forecast bringing a dangerous storm to your area, believe it. The storm might turn out stronger than predicted, or even weaker. But best to err on the side of caution.

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