Hurricane Rita, 2005. (NOAA)

On Sept. 26, 2005 when the National Hurricane Center stopped issuing advisories on Tropical Depression Rita, which was then centered near where the Louisiana, Arkansas, and Texas borders meet, we were roughly at the mid-point of the deadliest, costliest and most active hurricane season in recorded history.

The 2005 hurricane season set at least four records:

  • The most tropical storms with 35 mph winds: 28
  • The most storms that grew into hurricanes with 74 mph or faster winds: 15
  • The most major hurricanes with 111 mph or faster winds: 7
  • The most Category 5 storms with 157 mph or faster winds: 4

These hurricanes caused an estimated 3,913 deaths and damage estimated at $159.2 billion with five of the season’s seven major hurricanes—Dennis, Emily, Katrina, Rita, and Wilma responsible for most of the deaths and destruction.

A perfect year to study hurricanes

The unprecedented number of hurricanes, especially major hurricanes made 2005 the perfect year for the huge “Hurricane Rainband and Intensity Experiment” (RAINEX), the field phases of which took place from Aug. 15 through Sept. 30, 2005. Scientists are still analyzing the data and working to use what they’re learning to improve forecasts, especially forecasts of how strong hurricanes will be when they hit.

RAINEX scientists collected immense amounts of data from hurricanes Katrina, Ophelia, and Rita. While Katrina and Rita were monsters that strengthened to Category 5 storms and then weakened to Category 3 before hitting land, Ophelia fluctuated between being a tropical storm and Category 1 hurricane at it moved to the northeast off the East Coast doing only minor damage. RAINEX scientists collected data from Ophelia when it was growing into a hurricane over the Bahamas.

Selecting 2005 for the experiment years in advance to allow time to plan and organize it was just good luck, says one of the project’s principal investigators, Shuyi S. Chen, a professor of meteorology and physical oceanography at the University of Miami.

Chen said in an email that she and the other principal investigators started working on the idea in 2001 and submitted the original proposal to the National Science Foundation in 2002, long before anyone could have predicted 2005 would be a busy season.

A key focus of the experiment was the “eyewall replacement cycle,” which strong hurricanes often go though as they weaken and strengthen. Scientists have known about and observed this cycle many times since the early 1980s, but knew relatively little about exactly how it works.

Eyewall_replace2 (USA Today Weather Book)

The best eyewall replacement data were collected from Hurricane Rita on Sept 21 and 22 as the storm’s primary eyewall shrunk as it intensified into a 180 mph Category 5 hurricane on Sept. 21. That same day a secondary eyewall formed and on Sept. 22 the old eyewall faded as the secondary, larger eyewall replaced it and Rita weakened into a Category 4 storm.

The in-the-storm research on Sept. 22, 2005 illustrates how RAINEX scientists collected data.

One of NOAA’s two P-3 “hurricane hunters” airplanes, which are equipped with Doppler radars “intensively sampled the two eyewalls with repeated radial penetrations,” RAINEX scientists reported at the American Meteorological Society’s 27th Conference on Hurricanes and Tropical Meteorology in Monterey, Calif. in April 2006.

At the same time the second NOAA P-3 flew broad “figure-four” patterns that took it from one side of Rita, across the eye to the opposite side, then partly circled the storm to fly back through the eye to the opposite side, mapping the storm’s rain patterns and collecting other data.

A Naval Research Laboratory P-3, which was equipped with a more powerful Doppler radar than the NOAA airplanes, flew around the hurricane between the original and new eyewalls, in the area the researchers called “the moat.”

All of the airplanes released dropwindsounds—small packages of instruments that collect and radio back data as they drift down to the ocean under small parachutes.

Chen, of the University of Miami, said in an email that RAINEX was unique in that its operations center at the University of Miami directed multiple aircraft targeting features: (the eye, eyewalls, rainbands) that affect hurricane intensity and produced high-resolution model forecasts for flight mission planning together all in real time. “I think the innovative aircraft observation and high-resolution modeling together defines the RAINEX legacy. “

Frank Marks, director of NOAA’s Hurricane Research Division in Miami, emailed that: “I would say that the results from RAINEX per se have had some impact on improving intensity forecasts,” but not the way (those involved) thought they would. The biggest improvements in the intensity forecasts from the Hurricane Weather Research and Forecasting model, which the Hurricane Center has been using since 2007 “came about from a systematic attempt to improve the model representation of the physics and dynamics of hurricanes. “

He says the RAINEX data were “a significant proportion” of the data used to test the model’s depiction and evolution of hurricanes. “As a result of these improvements together with increased horizontal resolution … the model was much more responsive to environmental changes like shear and dry air.

“While we did not purposely attempt to get the model to do eyewall replacement cycles the model is now creating them, and sometimes even doing it when the real storm does so.

“The current HWRF is by far the best operational hurricane model for intensity guidance. However there is more that needs to be done and I am sure that some of the RAINEX observations will contribute to improvements likely in a composite sense,” Marks said.

When asked about RAINEX, Hugh Willoughby, who is now a research professor at Florida International University and who was a NOAA’s Hurricane Research Division scientist from 1979 until 2002 and its director from 1995 to 2002, emailed that:

“As with other large meteorological field studies,  the basic rationale got subjected to careful scrutiny, new theories got advanced, and the science moved forward at a faster pace than would have happened without the experiment. Another, perhaps even more significant, positive outcome is that students and early career investigators become involved.”

Nevertheless, he wrote, RAINEX, like other large meteorological field programs in the past, “did not deliver a forecasting panacea, but it did move the science forward of itself and fostered advances made by a wider circle of investigators. Given the immense economic value of better intensity forecasts, I’d argue that it was a success, even in terms of MBA-think.”