Climate Forecasting in the Era of Category 6 Hurricanes
From predicting D-Day waves in WWII to the AI forecast and hurricanes becoming so strong that a new category is needed
In 1943, amidst the chaos of World War II, young oceanographer Walter Munk stumbled upon a critical revelation while aiding the war effort in Washington, DC: the erratic behavior of waves could jeopardize Allied plans to land troops in North Africa, causing huge casualties before the troops ever set foot on land.
The problem was the shifting shape of the ocean surface.
Waves at the proposed landing site were consistently higher than the safe limit, making the landing likely to fail unless it occurred on a calm day. The only options for success were blind luck or something no one had ever attempted: predicting waves, an endeavor unprecedented in naval strategy.
Teaming up with his previous boss and mentor, Harald Sverdrup, the Director of the Scripps Institution of Oceanography, they convinced the skeptical US Navy.
And so, they embarked on a project that would change the course of history.
A Forecast to Turn the Tides
Their approach was straightforward: understand the entire journey of waves from their inception to shore.
When air blows on a smooth surface like a glass of water, it pushes downwards, creating a dimple. This disturbance ripples across the surface due to surface tension. Similarly, waves in the ocean begin with the ever-shifting swirls of the turbulent air above, which create puffs of faster wind and changes in pressure, distorting the surface. As the wind blows sideways, it pushes on the upwind side of each ripple, causing the ripple to grow into a longer-lasting ocean wave, traveling in different directions with energy given by the wind.
Munk and Sverdrup, although lacking detailed knowledge, recognized that the mixture of wave sizes depended on the wind speed and the distance it had been blowing over the ocean. They used weather forecasts to predict wind-caused waves in the open ocean.
However, the problem for landing craft wasn’t the wind sea; it was about anticipating the aftermath of distant storms — the swells — that could wreak havoc on landing sites.
Waves are a shape that must travel. So they had to account for the transformation of waves from storm to shore, where some lose their energy but others keep going. These smooth, leftover waves, known as swell, continue to move outward across the sea surface, carrying their energy even after the wind has died down. And can easily keep going until they reach a coastline.
Munk and Sverdrup accounted for the transformation of waves from storm to shore, where waves become steeper before breaking. By considering these three stages separately, they successfully predicted the wave height experienced by the landing craft.
The wave prediction model, although it was rough and ready, got the big picture right. And their predictions proved pivotal in history.
In the early summer of 1944, the end of WWII was near. The Allied forces were ready to launch Operation Overlord from the British coast in an attempt to retake Western Europe from a weakened Germany. The success of this operation relied on a surprise crossing of the English Channel, with 132,000 troops landing in northern France by ship in a single day. Another 24,000 troops would be transported by air. But it also depended on favorable weather conditions, including a full moon and the right tides.
And it was Munk’s forecasts that influenced General Eisenhower’s decision to delay the D-Day invasion. The difference between potentially disastrous waves on June 5th and a more manageable sea on June 6th determined the outcome of the invasion that turned the tide of World War II. The ocean waves that could have caused one of the greatest wartime disasters for the Allies arrived on June 5th, but a day later, the ocean shape had changed; and so the most decisive amphibious landing in human history had far milder waves to contend with.
Munk and Sverdrup’s work laid the foundation for today’s wave and swell forecasts, shaping maritime operations worldwide. Yet, their story isn’t just about waves; it’s a reminder of the impact that understanding the ever-changing climate can dictate the fate of human history.
Transforming Forecasting with Deep Learning
So ever since World War II, computers have revolutionized weather forecasting, simulating the future state of the atmosphere and predicting everything from severe storms to heatwaves.
The gradual but steady improvement in weather forecasting, known as the “quiet revolution,” has significantly improved the accuracy of forecasts since Munk’s days. Today, a 6-day forecast is as reliable as a 3-day forecast from 30 years ago. This has saved lives and money by ensuring that severe storms and heatwaves catch people off guard.
However, traditional weather models come at a high cost, with billions of dollars spent on energy-intensive supercomputers that run continuously to produce a limited number of forecasts per day.
Now, artificial intelligence (AI) is reshaping this landscape.
Tech titans like Google, Huawei, and Nvidia have harnessed AI to predict weather patterns up to 10 days in advance with an accuracy topping traditional models. Google also has a short-term AI weather model that makes rolling 24-hour predictions that are more accurate than nearly any weather agency’s. Even the European Centre for Medium-Range Weather Forecasts (ECMWF), a leader in weather prediction, has embraced this shift, developing experimental AI forecasts. And other weather agencies are scrambling to catch up.
Unlike traditional models reliant on solving complex equations, these AI models employ “deep learning” to forecast based on learned patterns from 40 years of ECMWF “reanalysis” data — observations and short-term model forecasts that represent modelers’ best and most complete picture of past weather. As in with D-Day wave forecasting, this is progress on a task that was thought infeasible just a few years ago: AI models deliver forecasts in a fraction of the time, running on a desktop in mere minutes instead of hours on supercomputers, meaning they are also less energy intensive.
The new AI models aren’t perfect: they are an ongoing process. But as they evolve to learn directly from real-time weather observations, their potential for revolutionizing weather forecasting grows exponentially.
Meanwhile, challenges remain, especially when predicting extreme weather events in an increasingly unpredictable world.
One that may have to add a new hurricane category.
Brace For Impact: Hurricanes Bringing Off-Charts Intensity
With climate change fueling tropical cyclones, it might be time to upgrade the hurricane scale to include a Category 6 for these monstrous storms.
A recent study in the Proceedings of the National Academy of Sciences argues that the escalating fury of tropical cyclones due to global warming demands a new classification: Category 6. Typically, hurricanes in the Atlantic and typhoons in the Pacific are graded on the Saffir-Simpson Hurricane Wind Scale from Category 1 to 5 based on their maximum sustained winds. However, the scale stops at Category 5 for storms with winds exceeding 157 mph.
However, according to this study, it’s time to acknowledge the unprecedented ferocity of these storms by extending the scale to include Category 6 for exceptionally intense tropical cyclones. Here’s why:
1. Rising Intensity:
While the total number of hurricanes has remained steady, climate change has been fueling more destructive hurricanes over the past four decades.
The IPCC says it is likely that the global proportion of Category 3–5 tropical cyclone instances has increased globally over the past 40 years, and the ratio of Category 4–5 TCs will very likely increase globally with warming. And even basic physics supports that hurricanes get more intense as the climate warms, with climate models showing evidence of strengthening tropical cyclones, with recent major Tropical Cyclones (TCs) have reached extreme wind speeds above the 157 mph threshold.
Jeff Masters, a meteorologist at Yale Climate Connection, told Bloomberg Green that “every 1 degree Celsius increase in ocean temperature increases a hurricane’s destructive potential by 50%”. And the new study suggesting the addition of Category 6 has also found that with every two degrees Celsius of global warming above pre-industrial levels, the risk of one of these Category 6 storms increases by up to 50 percent near the Philippines and doubles in the Gulf of Mexico. The highest risk of these storms is in parts of Southeast Asia and Australia, the Philippines, and the Gulf of Mexico.