The director of the National Oceanic and Atmospheric Administration’s forecasting lab says the federal government is still relying partly on computer models designed for much larger weather systems to predict what hurricanes will do.
Alexander E. (“Sandy”) MacDonald, Director of NOAA’s Forecast Systems Laboratory in Boulder, CO, says a more precise model is in the works that would allow for sharper predictions.
But getting it ready for deployment will require more computation and research dollars. “We have a ways to go,” he tells Technology Review’s Chief Correspondent, David Talbot, who interviewed him this week.
TR: The Katrina forecast was extremely accurate, but Rita wound up farther north than initially predicted. This meant the evacuation of Houston was perhaps not as necessary as the evacuation of New Orleans. Weren’t the same computer models used for both forecasts?
AM: Forecasters use as many as ten different models – that’s called a model ensemble – to try to determine what the hurricane track and intensity are going to be. It’s sort of like you call ten stockbrokers and say “What’s the best stock?” You use all of that information to come up with the best forecast. Hurricane Katrina was a very accurate forecast, partly because the models were very accurate. For Hurricane Rita, the models were quite widely varied in their predictions, so that was a harder forecast. This showed us that we still have improvements to make to the models.
TR: What accounts for the fact that the models agreed with each other with Katrina more than for Rita?
AM: The differing levels of atmospheric stability. A hurricane can become trapped between two high pressure systems, which creates a stable “chute.” An unstable situation is that there’s no “chute” – there’s just kind of an open area without high pressure systems, and the hurricane can go any which direction it wants. Katrina was more trapped – it had to go the direction it was going. Rita depended on pretty small differences in the pressure around it as to which way it would go.
TR: Improving models starts with collecting more hurricane data. How can this be improved?
AM: Right now we get measurements of a hurricane every six hours with a manned plane that carries “dropsondes” – similar to weather balloons, except they measure winds, temperature, and pressure as they fall from the plane to the surface. But you could actually have an unmanned aircraft system, a UAS, ride along above the eye of the hurricane, at 65,000 feet, and it could release a dropsonde every hour, providing almost continuous measurements in the center of the storm. That is something that we can’t do now. The UAS could have instruments, either microwave or radar, that could tell us continuously the surface winds based on the waves and other ocean signatures. That is an example of something that would be possible.
UASs are one tool, but there are a number of others: more buoys with weather and ocean sensors on the water’s surface, more manned aircraft, better usage of satellites. We could also use Doppler radar on the manned airplanes to measure the hurricane eyewall wind structure, which can be inserted into the model to improve prediction.