As Hurricane Melissa approached Jamaica last month, a NOAA Hurricane Hunter airplane dropped a fleet of weather instruments called dropsondes into the depths of the storm. Each dropsonde parachuted through the raging winds and pouring rain, beaming a stream of data readings on pressure, temperature, humidity, and wind back to the plane. Right before one of the dropsondes plunged into the ocean, it reported a measurement that caught the team’s attention: a wind gust reading of 252 miles per hour. Had they just captured the strongest hurricane wind ever recorded by a dropsonde? 

When the National Hurricane Center received the dropsonde data from the plane via satellite and processed the 252 mph reading, they cautiously began referring to the measurement as a potential record. In order to verify the reading, they contacted researchers at the U.S. National Science Foundation National Center for Atmospheric Research (NSF NCAR), where dropsondes were developed, and asked them to look at the data.  

“NOAA looped us in when they saw the high wind speed and asked, ‘Are these numbers any good?’,” said Holger Vömel, an NSF NCAR senior scientist who works with the organization’s Dropsonde Program. “They have pilots and researchers literally putting their lives on the line to get these measurements. They’re the heroes, and it’s a privilege we get to play a role in making sure the measurements they acquire are accurate.” 

View from inside a hurricane

Dropsondes are small cylindrical devices that are used by organizations like NOAA to collect valuable information during extreme weather events like hurricanes or atmospheric rivers. As they fall to the surface under a small parachute, dropsonde sensors gather information that helps shape forecasts and inform communities of approaching hazards. Fifty years ago, scientists at NSF NCAR created the modern dropsonde. Over the decades, new generations of NSF NCAR researchers have continued to update dropsonde technology, and the latest version – the NRD41 which is manufactured by Vaisala – is the only operational dropsonde in the world. 

NSF NCAR staff are continuously advancing  dropsonde technology, including the development of tools to analyze the data from dropsondes. In order to verify the wind reading from Hurricane Melissa, Vömel and other NSF NCAR researchers scrutinized the data and ran it through a post-processing software called Aspen that performs quality control. They checked that the reported numbers tracked with the laws of physics and typical behavior of hurricanes and that there were no gaps in reported measurements. When no anomalies were found, they confirmed that the measurement could be trusted. Hurricane Melissa’s 252 mph wind gust surpassed the previous record from Typhoon Megi over the Western Pacific in 2010, where a dropsonde measured wind gusts of 248 mph. 

Previous potential records have not always passed that same rigorous test. For example, during Hurricane Katrina an even stronger wind was suspected, but ultimately when the researchers looked at the data they found substantial issues with the numbers collected by the dropsonde and the record was discarded. 

Having accurate data on what is happening inside of a hurricane is crucial for forecasting and emergency alerts. While other instruments can measure elements like pressure, temperature, humidity and wind, none of them can get all four of them at once while inside of a hurricane. Dropsondes take measurements 2-4 times per second as they fall through the sky, allowing researchers to look at a slice of a hurricane in incredible detail. Dropping multiple dropsondes simultaneously offers a holistic picture of what is happening inside a storm and how it will affect communities in its path.

In the case of Melissa, the powerful winds and storm surge went on to inflict catastrophic damage on Jamaica, Haiti, and other Caribbean nations, killing close to 100 people. The toll would almost certainly have been even more grim if the storm had not been well forecasted.

“When you’re looking at a category 4 or 5 hurricane, you’re not going to have an airplane flying that close to the surface – that would be totally unsafe – but you need to know what is happening near sea level because that’s where people and property are most affected,” said NSF NCAR engineer Terry Hock, who manages the Dropsonde Program. “The dropsonde gets you information you can’t get any other way and that’s why it’s been around for decades.” 

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