During hurricane season, meteorologists — like some of you — look at forecasting models on computers until they get sick of it. We look several times a day to see what’s on the horizon. Will there be a storm? Where? When? If one model shows a storm, we look to see if another model shows the same thing to try to verify the forecast.
But in reality, models often just don’t agree—and this can be one of the most frustrating parts of our job.
“Hurricane prediction models are incredibly complex. There are different ways to adjust them, so to speak,” said Greg Carbin, head of operations at The Weather Prediction Center.
“You don’t know exactly what the atmosphere is doing at every point on Earth at the initial moment, so you have to make certain assumptions.”
The initial time is the starting point for the model to derive the forecast.
Because of this, the models will have slightly different predictions for events that will occur within a few days. Sometimes the difference is extremely small, but if a major storm is about to hit the U.S. coast — actions to get out of the area need to be ordered, shelters opened and emergency teams installed — 30 miles of uncertainty could end up costing billions of dollars. dollars. So the pressure is a lot.
“Each model has very unique parameterizations, they’re called, and unique equations to drive your prediction output,” Carbin said.
“And in some scenarios, some hurricane prediction models are better. And in other scenarios, different models are better. And so, we are always pushing the envelope, so to speak, when it comes to these complex numerical templates.”
That’s why we often show various models on TV when predicting a hurricane or a storm. We do this so you can see the discrepancies and various possibilities of what could happen — because it’s often impossible to know with 100% certainty what the forecast will be.
With that being said, models have improved dramatically over the years, especially when it comes to short-term predictions.
“A three-day forecast today for rainfall and temperature is as accurate as a one-day forecast was about 10 or 15 years ago — but there is a limit to that predictability,” Carbin said.
Any hurricane prediction model beyond a week should be viewed as small.
After a week, models start to lose their credibility. Sometimes we look at a forecast model and we see a potential Category 3 hurricane hitting the Gulf Coast two weeks from now and we start to shrink.
In fact, if you look at the Global Forecast System today, there is a Category 2 hurricane hitting the Virgin Islands on August 30th, with another storm close behind. The truth of the matter is that predictions so far away are as accurate as a shot in the dark.
“Beyond five, six, seven days, it’s really a fantasy storm. These storms probably don’t exist in real time. They should be taken lightly,” Carbin said.
If it’s hard to know exactly what’s happening in the atmosphere on day one, imagine the error when models are predicting day 14.
Carbin made an interesting analogy regarding the unreliability of long-term forecasts. He explained that if you went fishing and put a cork in a river in the same spot over and over again and watched it float 100 meters downstream — it would end up in a different spot each time.
Likewise, it’s impossible to know exactly the dynamics of the environment a week later, so the Category 3 storm that a computer model forecast will hit your city in two weeks — you can bet money it probably won’t.
“The reason is because the ‘flow’, like the atmosphere, is a complex system. There’s a lot of chaos, there’s a lot of factors there that you can’t really explain because it’s its complexity and its dynamic nature. Computer models for the atmosphere likewise,” Carbin said.
But that doesn’t mean we shouldn’t be alert and ready for anything. It’s hurricane season, after all, and the models offer wonderful guidance on what’s going to happen—especially in the short term.
Carbin advises looking at climatology when predicting the tropics over seven days. Focusing on that will likely give you a better forecast than obsessing over long-term forecasting models, he said.
August is when the hurricane season really starts to pick up. So if you look at climatology, it wouldn’t be out of the question to see a storm impact the Virgin Islands or other Caribbean islands.
But we also have a good chance of seeing something a little closer to the American continent.
So while we take these long-term predictions with a grain of salt, we also need to be ready for anything as we approach the peak of hurricane season.
Source: CNN Brasil
