Hurricane Otis, which struck the Mexican resort of Acapulco last week, killing at least 39 people, was the strongest storm to hit the country’s Pacific coast, according to local authorities. At the same time, the day before the strike still looked like a relatively harmless storm, and no one had any idea what it would bring. The rapid transformation from a tropical storm to a powerful hurricane was then detected too late for the people of Acapulco to prepare.
According to Briant Tang, an atmospheric expert at the University of Albany in New York state, the disaster exposed the continuing limits of weather forecasting and the importance of aerial monitoring.
“This time of year, the wind direction changes and it happens that storm systems are pushed up to the Mexican coast, which is exactly what happened with Hurricane Otis. Unfortunately, the worst combination of other factors was added to this – the hurricane was born just off the coast and headed straight for Acapulco,” Tang told Seznam Zprávám.
One of the most debated factors that contributed to Hurricane Otis’ disastrous effects was the speed with which it transformed from a tropical storm to a Category 5 hurricane. How fast was the process and how unusual is it?
One day, Otis was a tropical storm with wind speeds of about 100 feet per second. Then came the rapid intensification – between morning and night, say in about 12 hours, Otis became a Category 5 hurricane with winds of 70 to 75 meters per second.
This is the fastest intensification within 12 hours that we have ever seen in the area.
Brian Tang teaches atmospheric sciences at the University at Albany. His research focuses on hurricanes and tropical cyclones, especially on the process of their formation and intensification.
It was unprecedented throughout the historical record only if we are talking about the hurricane zone of the eastern Pacific. In other zones, we could see even faster intensification of hurricanes.
Staying in the eastern Pacific, I see some analogy to Otis in Hurricane Patricia, which hit Mexico in October 2015. It also gained strength very quickly, but unlike Otis, it weakened again just before making landfall. It also hit a sparsely populated area, while Otis hit the city of Acapulco, home to about a million people.
How common are hurricanes this strong in this area in general?
In general, it can be said that the eastern Pacific is rich in hurricanes. But they mostly go from the coast of Mexico towards the central Pacific. However, during this part of the year, the direction of the wind changes and it happens that storm systems are pushed all the way to the Mexican coast, which is exactly what happened with Hurricane Otis.
Unfortunately, the worst combination of other factors was added to this – the hurricane was born just off the coast and headed straight for Acapulco.
How unprepared were the locals for the hurricane compared to the standard situation where the hurricane is predictable and weather models predict its behavior quite correctly?
Yes, this was another problem – the computer models we use to predict the strength of storms didn’t really estimate the rate of intensification in this case, so we didn’t have a clearer picture until just before, specifically about just a day before the hurricane made landfall. And it was too late. To prepare an urban area the size of Acapulco, you need at least a few days’ advance notice. We can say with certainty that the residents did not have enough time.
On the other hand, it must be said that even if the warning came in time, the preparations would probably still be problematic and the damage great. Not everyone follows the forecast and takes it seriously. Otis, with or without the prediction, would only materialize right before the strike.
Photos: Acapulco in ruins
I understand that it must take some time just for people to process the information and get the impression that they should take the warnings seriously. But what else must the city and residents do in preparation for a hurricane to minimize damage and loss of life?
The most important and at the same time the most difficult thing for people in threatened areas is to prepare for the possibility that they will have to evacuate. In such a case, people need to collect things around the house that could fly away, or if there is a threat of flooding, move them somewhere safe, board up the windows, pack their things and come up with a plan for where they will go in the event of a final evacuation order in all this chaos . It’s a tall order. If you only have 12 hours for it, in my opinion, it is unachievable. Not even one whole day is enough.
As for the local government, it needs to get supplies to selected locations, set up shelters for those who have nowhere to go, and generally mobilize and organize a large amount of people and material. Therefore, it is commonly stated that at least several days are needed to prepare a large metropolitan area for a hurricane, even one weaker than a Category 5 hurricane.
Lack of data from satellite images due to cloud cover is cited as one of the main reasons why computer models did not predict the rapid birth of the hurricane. But I don’t understand that. Isn’t it the case that cloudiness is exactly what satellite images are supposed to track and show?
The thing is, to have a good forecast model you need to see and know a lot more than what the clouds look like. Wind direction, temperature, humidity and a whole host of other factors and processes that take place directly in a hurricane are also key.
So the problem is rather that in this part of the world we don’t have regular aerial monitoring, like we do in the North Atlantic, for example, where it is carried out by both the US Air Force and the National Oceanic and Atmospheric Administration (NOAA) whenever there is a storm that potentially threatens land . Airplanes collect data that greatly increases the accuracy of models, satellites measure temperature and other variables very well, but only where there are no clouds.
So, in the case of Hurricane Otis, there was nothing out of the ordinary with the clouds or the satellites compared to other hurricanes. Satellite observation limits are the same for all hurricanes…
Exactly, and not just for hurricanes, it’s just as true for a whole range of storm systems and cloud cover in general.
You mentioned that the area is not subject to routine aerial surveillance. In the end, the plane went into the hurricane anyway. But I guess it was too late?
I don’t know the exact details, but it was most likely a US Air Force plane, as the US has a treaty with Mexico to monitor storms. But what is certain is that it was critically important, because it was the plane that caught the rapid strengthening of the hurricane. By the time we had the data, it was clear that the storm was starting to intensify really quickly and people in the impact area were in great danger.
Did we miss something else that contributed to Hurricane Otis’ strength being underestimated in time?
The main hypothesis is what we have discussed – that the lack of direct observation was the cause in the first place, because of which it was not realized that the computer model started the prediction based on the wrong input information. However, I believe that this theory and the whole of Hurricane Otis will become the subject of thorough research by a number of scientists. Only from them will we learn the correct answers.
After all, this is how it goes in the long term. No forecast is perfect, and we are constantly learning from our mistakes and improving our models to better match the physical processes inside hurricanes. I think Otis is another important piece to the puzzle.
But to get back to your question – we haven’t mentioned yet that Otis was very powerful but also very small and compact. This was another tricky feature that made it difficult to predict.
Can you say what effect climate change might have had on the course of the hurricane?
No one can say if it was climate change that caused Otis. But what we can say is that if we look at storms like Otis, storms that intensify very quickly, there is some evidence that they are increasing. Especially in coastal areas where the water tends to be warmer.
We only have these scientific findings in recent years. If it is confirmed in the future and the trend continues, we may have to deal with the problems we saw with Hurricane Otis more often.