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Don Paul: Hurricane Irma – the monster and the myth

For many, Irma lived up to or exceeded its awful expectations. For others, the end result was less impact than expected. In sum, however, Irma will be the most expensive natural disaster in U.S. history, and may well exceed the most pessimistic expectations on economic impact, not to mention human misery.

Farther east in the Atlantic and into the Caribbean, Irma broke the record for the longest consecutive number of hours during which top winds of 185 mph winds occurred with a hurricane in the Atlantic basin. When it made landfall in the Keys, Irma arrived as a Category 4, and went to Category 3, then 2 as it moved to southwest Florida and then east of I-75. That inland path was the saving grace for the Tampa metro area, not only reducing wind strength but substantially reducing the life-threatening storm surge threat from Naples up to Tampa and the rest of the west and panhandle coasts. At the same time, that inland path increased the threat to the Orlando area, and especially the flooding and storm surge threat to Jacksonville.

So, what’s the myth? Some think the National Hurricane Center didn’t do a good job with the track forecast. Many in these segments feel the west side of Florida received scant warning they would face major impacts. There are a host of reasons for that misconception and overdone expectations for near perfection. Many in the public and some in the media don’t understand the “cone of uncertainty” in the track forecast. NHC is quite clear about the existence of uncertainty, but a lot of that gets lost in the translation due to inattention. Here is the detailed NHC explanation of the cone, and the absolute necessity for its existence.

Many people focus on the center of that cone. Many TV graphics systems display the center line clearly implying “this is it” for the track. Frequently, that’s often far from reality. NHC works hard to communicate necessary uncertainty on the track, even when confidence is growing. Here is a statement from 5 p.m. Friday on Irma and its expected (and later realized) turn to the northwest: “The precise moment of this turn is still uncertain, and that is why NHC emphasizes that nobody should focus on the exact track of the center.”

It’s the CONE, gang, not the center line in the cone. As I wrote in an article last year, the atmosphere is not made up of Lego blocks which fit neatly together; it is a mix of almost countless variables, entirely dependent on laws of physics, including thermodynamics, which interact in different ways every time, every hurricane. We’re dealing with fluids and gases, unevenly heated; occasional intrusions of drier air that weaken storms; interaction between storm circulation and terrain increasing disruptive friction, even more when there are mountains involved as in the case of Cuba; and winds aloft shearing into the upper storm circulation and slowing it.

In the case of Irma there was the mathematical and physical juggling between the factors of even warmer than normal virtually hot waters in the Florida straits versus the interaction with Cuban terrain. There are no neat equations that can quantify with precision how much weakening from the terrain interaction can occur in a hurricane. Yes, even with powerful supercomputers, even with a plethora of models and their ensembles, even with large improvements in track forecast accuracy in the last decade, precision remains elusive and will remain elusive. Track forecasts will continue to improve, but they almost certainly will never become perfect.

Once NHC extended the cone northward to central Florida, at no time was Naples, Fort Myers or Tampa NOT in that cone, even before the track forecast began to shift to the west.

Click this link for a view of the storm track from the NHC.

You may note NHC took the shift far enough west to remove Miami and Fort Lauderdale from the cone for some time. But, all the while, NHC maintained the hurricane warning for the entire east and west coasts of Florida, including Miami. We knew the vast diameter of Irma would still bring major impacts to southeast Florida even with a more westward track.

In fact, the diameter of Irma made major statewide impact inevitable, with widespread destruction, even as some parts of the state escaped the worst. There were important variations of storm surge dependent on the precise track, yes, but it was a foregone conclusion days in advance this would be an unprecedented disaster in scope for Florida.

Now, we can only imagine the humanitarian crisis in the Keys, the destruction of the grid that will leave some locations without power for weeks. There’s the heat, the humidity, the danger of businesses closing and employees losing their jobs due to the longevity of the closures. The loss of power will be impacting dialysis centers and some hospitals. We can imagine the mass hopelessness and depression for tens of thousands of affected Floridians who have seen their homes become uninhabitable; the destroyed cars; and less than half of Florida homes had flood insurance. Speaking of insurance, how many insurance companies may go belly up in coming months because of the incalculably large payouts that are coming between Harvey and Irma? What does that do to property insurance costs for all of us in the future? So far, the loss of life has been low. Some of that is due to timely advanced warning and preparation. As for the physical catastrophe, we’re only just beginning to grasp its grim scope.

No, the track forecast did not approach being “spot on” the whole way in this long-lived and vicious tropical cyclone. It was, however, a critical element in keeping a huge population informed as to the dangers and the rare size of the threat, and the most likely probabilities for this raging monster’s behavior.

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