The best way to gather information about hurricanes is to get as close to them as possible. The U.S. Air Force (USAF) has been flying missions into tropical cyclones since World War II, initially as part of a warning system for civilians and later to improve scientists' understanding of these storms. The USAF is still flying research missions into hurricanes, but shares this role today with the National Oceanic and Atmospheric Administration (NOAA), with whom I have been lucky enough to fly.
Several types of airplanes have been used for hurricane hunting missions, but NOAA has been flying a pair of Lockheed P3 Orion four-engine turboprop aircraft—nicknamed Kermit the Frog and Miss Piggy—since 1976. Over the years, various instruments have been installed. Some, such as different types of radar, in-situ probes, and a stepped frequency microwave radiometers (SFMRs), are long-term residents that provide crucial information to forecasters and numerical weather prediction models (NWPs).
Into the air
Hurricane flights require careful planning. Generally there are two teams involved; flight operators from the Aircraft Operation Center, and scientists most often from the Hurricane Research Division of NOAA's Atlantic Oceanic and Meteorological Laboratory. Flights are scheduled around the times the NWPs are initialized. Typically there are two flights; one departs at 4 a.m. (the unlucky crew) and a second leaves at 4 p.m. (the lucky ones). Flight plans are devised by the research team and reviewed by the flight team. The most common patterns flown are called "Figure 4", "Butterfly," and "rotated Figure 4", of all which feature a radial penetration of the storm and circumvention of it in a downwind direction.
Flights can be long, but rarely last more than about seven or eight hours. It can take two or three hours just to reach the storm, during which time the scientific team reviews current data and may adjust the flight pattern as a result. Both teams also use this time to ensure that their computers and instruments are ready to operate, as well as get in some relaxation before starting hours of work in a turbulent and stressful environment.
Into the eye
Years ago hurricane aircraft missions were flown very close to the sea surface. Today, because of security measures, low altitude flights happen rarely, and only in weak systems. Flights usually aim to pass through storms at the altitude where air pressure is about 700 mb (approximately 3 km above sea level), but this can be altered depending on the weather conditions and if there are other aircraft sampling the storm at the same time.
As the plane begins its radial penetration of the storm, you usually experience minor turbulence. Looking out of the window, the view gets darker and darker toward the storm center. Screens in the plane often relay quantitative information confirming your visual estimate of what is going on outside. The belly radar provides a good image of the storm structure as the eyewall gets closer. A "swish" sound in the back of the plane indicates that a dropsonde has been launched, and soon after the wind and temperature vertical profile of the eyewall are displayed on the dropsonde analyzer computer screen.
Going into the eyewall, if not more turbulent, is certainly noisier as the plane works harder against the strongest winds. Then, the winds subside and a clearing appears—the eye at last! The pilot will linger so pictures can be taken if it is really clear and stadium-like in the eye. Central pressure is measured, the center itself is located, and data will soon be sent to the National Hurricane Center. The plane then exits the eye, continuing its radial route through the storm system and completing the flight pattern with more penetration, radar measurements, and dropsonde launches before flying back to the base. All the data collected is used for forecasting and/or research. (The nature and uncertainty of data gathered by aircraft reconnaissance is discussed in our AIR Current on Best Track Data.)
Into the future
Although the NOAA P3s and USAF planes are the only manned aircraft actually penetrating hurricane eyewalls in the Atlantic, there are other planes flying in hurricane environments. NOAA has a Gulfstream IV-SP jet that flies at high altitude measuring storms' environments. Increasingly, unmanned planes (a.k.a. drones) are being used to gather data; NOAA's 3-foot-long Coyote drone and NASA's 44-foot-long Gobal Hawk are two examples. However, despite all of the new opportunities for data gathering that these machines open up, there is nothing that beats the exhilaration of flying into the eye of a hurricane yourself!