"Unprecedented." "Unknown." "Beyond anything experienced."
When weather forecasters needed to describe Hurricane Harvey's potential for death and destruction, they stretched their linguistic abilities into new territory.
Here was a storm system with 130 mph winds — strong enough to topple tall structures — and rains that would be so relentless that millions of gallons of water would fall for days on vulnerable towns and cities.
Hurricane Harvey's power was so vast that it provided one of the most important lessons of weather forecasting: words matter. They can make the difference between life and death. Residents need to not just hear or read, but to grasp how dangerous the storm will be. Rescuers and aid groups need to know how extensively their services will be needed, and where.
So in one of the most memorable moments in forecasting history, communications teams at the National Weather Service found themselves scratching their heads. They needed new language and a new approach in graphics to capture the severity of the storm.
Hurricane Harvey made landfall on the Texas coast late on Friday as a Category 4 storm, a designation meaning it was capable of causing devastating damage. Even though the hurricane was downgraded soon after making landfall, it was expected to linger, prompting the National Weather Service to warn on Sunday: "This event is unprecedented and all impacts are unknown."
Since then, at least 10 people have been killed and many more injured in the storm, which had unleashed more than 50 inches of rain by Tuesday with the expectation that more will fall through today.
Officials have been grasping for superlatives. Gov. Greg Abbott of Texas called the storm "one of the largest disasters America has ever faced." Local, state and federal officials have conceded that the scale of the crisis is so vast they were nowhere near being able to measure it, much less fully address it.
Words may escape politicians, but measuring and describing a storm is exactly the job description of forecasters.
"We wanted to convey the message that this is a storm that can kill you," said Dennis Feltgen, a meteorologist with the National Hurricane Center in Miami.
While Feltgen noted there were similar dire warnings for other devastating hurricanes like Katrina in 2005 and Sandy in 2012, Hurricane Harvey stood out. The predicted deluge of up to 50 inches of rain tops what Houston receives in a year.
"It is unprecedented in terms of rainfall," Feltgen said. "We use the terms catastrophic and life-threatening, and that is exactly what it was."
Mike Brennan, a meteorologist with the hurricane center, said much of their challenge lies in trying to make citizens visualize what a unit of measurement means. That sometimes leads to translating the arcane language of weather science.
"Twenty-five to 30 inches of rain is hard for people to picture what that means," Brennan said. "There is a whole social science angle to our product. It's not just the numbers. It is the hazard: 130 mph, well what does that mean?
"A storm surge is a different animal. You are talking about how many feet of water, and trying to convey this is a life-threatening storm surge," Brennan said. "This is going to be taller than your children, or higher than your house, and that's where you come up with catastrophic and life-threatening wording, and push that message out."
The National Weather Service has devised guidelines exactly for the purpose of making their predictions digestible. For example, some sizes of hail are described not just in terms of inches but in comparison to real world objects. Would you be more afraid of 4-inch diameter hail or grapefruit-size hail?
The forecasts also need to be tailored for the terrain. A few inches of rain could mean a flash flood in an area where there is already saturated ground, but might be benign in a drier region.
"You just can't throw science at them," Brennan said. "We are scientists, we like numbers and technical knowledge, but we need to use plain words."
"You have to turn people away from the particulars of the storm," he said. "People are bombarded with messages. So you try to point them to the hazards."
But true to its legacy, Harvey evaded description, particularly when it was referred to by the weather service as "beyond anything experienced."