As of 8 AM Eastern Time, Hurricane Dorian remains a devastating Category 5 storm slowly grinding its way across Grand Bahama. The latest storm tracks projected by the National Hurricane Center continue to suggest that Dorian will hug the coast as it moves slowly northward, but Florida may be spared a direct blow. Even so, the storm will bring torrential rain over a large area of the coast, with flash flooding from Florida through the Carolinas and a storm surge that threatens hundreds of miles of coast.
Images that have already come out of the northern Bahamas are heartbreaking, and they are sure to be only a fraction of the destruction still to be revealed when the storm is past. The speed of the winds has decreased somewhat—to an only jaw-dropping 165 mph following Sunday’s insane 185 mph—but the second most powerful Atlantic hurricane on record is still grinding its heel on the people of Freeport with a fury that is hard to believe.
At 8AM, the storm is traveling to the west at only 1 mile an hour. That creeping progress means more punishment for those currently at the center of the swirling winds. But it’s also exactly what is saving the United States from facing this storm.
A weak (very weak) high pressure system in the North Atlantic has for the most part being pushing Dorian to the west over the last few days, but that system has also been collapsing. As it degrades, Dorian will be more subject to systems to its west and south that will begin to steer it northward. Had the storm’s pace taken it past Freeport overnight, it’s likely that northward turn would not have set in early enough to keep the core of Dorian from brushing the coast.
Dorian did not complete its pass over Grand Bahama. The eye of the storm is still barely at the midpoint of the island. That’s increasing the duration and extent of the disaster for Freeport and other communities in the Northern Bahamas. But it’s greatly increasing the possibility that Dorian does not plow directly into Florida and the odds that it will eventually curl back out to sea after dragging rain and surge all the way to Cape Hatteras.
But no one, no one anywhere in the Southeast region, should take that as certain.
Day after day, for better than a week, the intensity of Hurricane Dorian has exceeded the predictions of the best available models. To see how badly those models missed, looked at the the first of the National Hurricane Center’s advisories to indicate what Dorian would be like when it reached the Bahamas. Advisory 11, issued on August 26, predicted that Tropical Storm Dorian would cross Grand Bahama carrying winds of 70 mph. Three days ago. Or take a look at Advisory 31, which predicted the storm would hit 150 mph, just 24 hours before it reached 185.
This isn’t an attack on the model. The models used by both the National Hurricane Center and European agencies have been refined to the point where they may be, quite literally, very close to as good as they can get. Because … chaos. And yes, that may bring to mind a image of Jeff Goldblum dripping water onto Laura Dern’s hand while delivering some of the worst math-a-magical mumbo jumbo ever to mangle a theory, but there really are instances in which a system is so sensitive to initial conditions that even the brain sweat of the biggest supercomputers can only do that much better than a coin flip.
For what we consider a “normal” storm the models do a genuinely fantastic job of defining how a storm will behave hours and days in advance. Seizing on the single data point in that past advisory with the largest margin of error and pointing out how badly is missed may seem like an intentional effort to make the model look bad, but there are really two problems in this situation. First, there’s the source data. That data is bad because it’s insufficient to fully describe the situation at the detail necessary to resolve the very fine changes that are steering this storm. That’s particularly true in defining the well-known (but poorly instrumented) Bermuda High, which has the bad grace to be located over water so we don’t have a weather station poking into it every few miles. That’s the chaos thing again. But the other thing that could be wrong really is the model.
It’s not meant to model storms like this. There are no storms like this.
Sure. Dorian is only the “second most powerful” Atlantic hurricane, and maybe not even that depending on how the measurement is made. But it is also doing things that no storm on record has ever done. That’s particularly true in looking at the way it intensified.
Saying that the model missed the prediction on the intensity of the storm is only a part of what happened. Dorian’s growth from a tropical storm to a Category 3 hurricane wasn’t exactly expected, but it also wasn’t that unexpected. The way Dorian grew from a Category 3 storm to a Category 5 storm was something else, the speed with which it increased in intensity greatly outpaced any other storm on record. In automotive terms, there are many, many cars that can make it to 120 mph. There are better than two dozen vehicles that can reach 185 or higher. All of those cars are faster at going from 0-60 than they are at going from 60-120, and they’re all faster at going from 60-120 than they are at going from there to 180. Except Dorian. It didn’t work that way.
Since the intensity of the storm affects how it reacts to other weather systems and how it moves, the fact that Dorian intensified more rapidly than expected played into why it didn’t go where where it was expected. The two things are really part of one thing — the difficulty of forecasting behavior in slow-moving, wet storms.
And that’s what another model is trying to tell us. Or, rather, many models. Because the models that look at how the world is being impacted by the climate crisis have predicted that we won’t necessarily have more hurricanes in a warmer future, but we will have slower-moving, higher-moisture storms. Which are, once again, those storms that are most difficult to predict.
In a very real way, models of the climate crisis are telling us that models of hurricane movement are becoming, and will become, less accurate—even if they are very good models. Which they are.
It also means that, right this moment, people in the Bahamas, and Florida, and Georgia, and South Carolina, have lives and property that’s dependent on very tiny changes in weak weather systems hundreds of miles away from the hurricane itself. And the world can only wait to see what remains of Grand Bahama when the all but motionless storm finally moves away.
And a reminder that the ‘D’ in Dorian means we’re still quite early in this hurricane season.