by Alison Gillespie (NOAA Research Communications)
People generally want to know three things about any hurricane: when and where will it make landfall, and how bad will it be. Over the last few years, NOAA researchers have worked to enhance and expand their measurements of these large storms, aiming to improve forecasting and more effectively answer those three questions. In addition to some of the familiar tools from the past, we are now also using unmanned aircraft, new types of Doppler systems and sophisticated supercomputer-based modeling to discover more about hurricane behavior. The ultimate goal is to predict with consistent accuracy all of the details regarding the intensity of these deadly storm systems, as well as their anticipated paths across the ocean, in order to better prepare the public for coming dangers.
Some of the technology being used for hurricane forecasting will take us deeper into storms than ever before. The Global Hawk is a prime example. This year the unmanned aircraft will deploy dropsondes – small tubes filled with sensors, GPS microchips and tiny parachutes – into hurricanes to gather data on wind speed and direction, temperature, pressure and moisture. That information will be combined with data from satellite-based instruments to gain more insight into how these storms move. The work is being conducted in collaboration with NASA through a program called Sensing Hazards with Operational Unmanned Technology.
Another much smaller unmanned aircraft with a six-foot-wide wing span called the Coyote will make flights again this year into hurricanes; previous experiments in 2014 demonstrated it could be safely sent directly into the eye of a storm for data capture. This year researchers will use the Coyote to measure the strongest winds and collect continuous observations in the lower altitudes of hurricanes – areas that would otherwise be impossible to reach with manned aircraft.
In addition, underwater gliders will be used this season in both the Atlantic and the Caribbean for gathering data on storm intensity. Glider data gathered in 2014 was found to measurably improve forecasts when plugged into the experimental HYbrid Coordinate Ocean Model.
Researchers are working to gather more information about the areas immediately surrounding hurricanes, and as such a model used by the National Hurricane Center called Hurricane Weather Research Forecast (HWRF) will also receive a major upgrade to its code this summer. The HWRF provides our best understanding of the strength of tropical cyclones, by using observations gathered from satellites, Doppler radar, buoys, and hurricane-hunting aircraft to fashion 3-D images in order to assess the intensity of storms. The new code will improve understanding of incoming storms’ boundary layer and vertical wind structure, as well as increase the size of the region where the close-in, high-resolution calculations are performed around a hurricane. Improvements will also enable the HWRF to connect with a separate hurricane wave model.
A new Doppler Wind Lidar system is also under development at the Atlantic Oceanographic and Meteorological Laboratory, and could eventually be used to complement the Doppler radar already in use. Although often associated with modern television-delivered weather forecasts, the term “Doppler” dates to the 1830s, and is used to describe how waves of sound or light change as the source of those waves and the observer of the waves move away from each other. The new Lidar system works by sending out pulses of microwave energy and mapping their return signal strength and the Doppler shift to gather an estimate of the wind along a radar beam. While existing radar is used to measure the return sound signals and the Doppler shift from targets like raindrops or snowflakes, Lidar uses eye-safe pulses of light, and can measure the return and shift from much smaller aerosol particles, even when there is no precipitation. The most important measurements made in hurricanes are the wind; high winds can cause storm surge by pushing large amounts of water into coastal areas. Many of the fatalities and much of the property damage caused by hurricanes is due to the resulting floods. Once established, the Lidar system can be combined with existing Doppler radar to provide scientists a complete, high-resolution, 3-D representation of the wind in a storm as it builds on the ocean.
Scientists at NOAA’s Geophysical Fluid Dynamics Laboratory are also at work on forecast improvements. Currently, predictions about hurricane activity are focused on the entire Atlantic basin, which stretches from the coast of Africa through the Caribbean to the United States’ East coast. In the future, the GFDL team would like to narrow that window to a region the size of two states.
Some of the biggest technological improvements in recent hurricane research have come at a time when the storm seasons have been relatively light and the number of hurricanes making landfall has been small. Even so, the lessons learned from storms such as Sandy (2012) and Katrina (2005) remain seared into the nation’s memory as testaments to the need for preparation; a single hurricane can be a devastating and deadly event. By employing cutting-edge technology we can continue to fill the remaining data holes in our understanding of the formation of these massive storms, and their potential paths towards coastlines.