(This is the second of two stories about the Hurricane Reanalysis Project. The first story can be read here.)
There were many reasons why a small group of scientists undertook the daunting project of revising the official U.S. government record of hurricane activity affecting the U.S. and the Caribbean, but the bottom line was simple: the record wasn’t completely accurate.
It was originally assembled in the 1960s in support of the Apollo space program. Revisions, still ongoing, were started in the 1990s.
“The HURDAT (hurricane database) contained many systematic and random errors that needed correction,” is what the researchers said in a report on the website of the National Oceanic and Atmospheric Administration’s National Hurricane Center, explaining the rationale for their effort to revise the record.
“(A)s our understanding of tropical cyclones had developed, analysis techniques at NHC changed over the years, and led to biases in the historical database,” they added.
And then there was the work of Jose Fernandez-Partagas and a colleague, H.F. Diaz, uncovering information about numerous “missed” tropical cyclones during the second half of the 19th century and the early 20th century, which could not be ignored. The storms weren’t part of the official record, but there were ample historical references to them to know they should be.
“We need accurate records,” said Christopher Landsea in a recent interview with the Source. Landsea is chief of the National Hurricane Center’s Tropical Analysis and Forecast Branch and the scientist who has headed the Hurricane Reanalysis Project since the late 1990s.
The database is and has been used for everything from establishing building codes and setting insurance rates to helping experts recognize weather patterns and educating emergency managers on potential preparation needs, he said.
The Reanalysis Project researchers have moved primarily chronologically, studying a group of years at a time and periodically issuing reports on their findings, which are posted on the NOAA/National Hurricane Center website.
The first report covers the most years: 1851 to 1910.
In the early to mid-19th century, tropical cyclones (a hurricane or tropical storm) affected some ships at sea and some coastal areas, just as they do today. But if the coast was not populated and if the ship sank, no one ever knew. Even if there were witnesses to tell the tale, it could be weeks or more before others heard it, given the available communication methods.
Things changed rapidly over the next 50 years, as outlined in the report.
Telegraph lines began appearing mid-century, about the same time that the centuries-old anemometer was improved with the invention of the cup anemometer to measure wind speed and direction. In 1870 the Army Signal Corps (which eventually evolved into the National Weather Service) began. Five years later, the first hurricane forecasting system was started in Cuba. In 1898 the U.S. established observation stations throughout the Caribbean, and by 1905, ships were able to report storm sightings via radio. Meanwhile, the U.S. population was growing, and some of it settled on the coasts.
The project researchers estimated that from 1851 to 1885 there were an average of 0 to six storms each year that went undetected and unrecorded. From 1886 to 1910, primarily because of technical advancements, the estimate dropped to 0 to four “missed” storms each year.
The researchers also double-checked the paths and the wind speeds of the tropical cyclones that had already been noted.
They reported that based on their findings, they made “several thousand” alterations and additions to the official record between 1851 and 1910, including actually creating the database for 1851 to 1885.
Ensuing reports of later periods (1911 to 1920; 1921 to 1930; 1931 to 1943; 1944 to 1953; 1954 to 1963) all contain changes to the record, though not as many as in the first set of years studied.
The 1931-1943 report, for instance, says 23 tropical cyclones were added to the record and five systems previously considered tropical storms were deleted.
The 1921 to 1930 report makes note of another reinvention of the cup anemometer which made significant improvements in its ability to measure winds. The year 1943 marked the first time an airplane was intentionally flown through the center of a hurricane, enabling the transfer of data in real-time via two-way radio.
Website text describing work on the first half of the 1960 decade says revisions were accomplished “by obtaining the original observations collected – mainly by ships, weather stations, the Hurricane Hunter Navy, Air Force, and Environmental Science Services Administration (ESSA) aircraft reconnaissance planes, and the earliest available satellite images – and assessing the storms based upon our understanding of hurricanes today.
“The reanalysis also allowed ‘discovering’ of tropical storms and hurricanes that occurred, but were not yet officially recognized as such in the official records. Nine new tropical storms and hurricanes during these five years were discovered and added to the database. Six hurricanes were identified as impacting the United States, one less than originally identified.”
The Hurricane Reassessment Project has also resulted in changing the status of some well-known storms.
Hurricane Betsy, which killed 75 people in Florida and Louisiana in 1965 and was the first billion-dollar hurricane in damages, was upgraded from Category 3 to Category 4 on the Saffir-Simpson scale.
Hurricane Andrew in 1992 (studied out of chronological sequence because of the importance of its impact) was also upgraded, from Category 4 to Category 5.
Hurricane Anna, which was “a milestone as the first hurricane to appear in a satellite image” in July 1961, was downgraded from Category 3 to Category 2.
In assessing the strength of a storm system, there are many factors to consider, Landsea said. Primary among them is the wind speed as measured by an anemometer. The central barometric pressure is also important. Clues to its strength come after the fact in damage assessments, but those are “not straightforward” in all cases since there are multiple factors involved in causing damage besides sustained wind strength.
Technical advancements have allowed for more accurate assessments. Hurricane hunters, drones, satellite imagery, radar systems and other aids have improved the process of data collection tremendously, lending credence to the notion that there will be little need for reassessments in the future.
But for now, the project continues. The next report, covering 1965 to 1970, is expected well before the end of this year.
Landsea and his small team submit their recommendations for database changes to an oversight group within NOAA, the National Hurricane Center Best Track Change Committee, which has the final say. And they are open to exploring recommendations that come from outside the National Hurricane Center.
“Suggestions for change are certainly welcome, as the more people that become involved with the details of the reanalysis effort, the better the final product should become,” according to text on the website.
Those interested can see how to submit recommendations for changes and view detailed reports on project phases, online at the NOAA website.