New Re-Analysis Sheds Lights on the Mysteries of Hurricane Camille

On the night of August 17, 1969, mighty Category 5 Hurricane Camille smashed into the Mississippi coast with incredible fury, bringing the largest U.S. storm surge on record--an astonishing 24.6 feet in Pass Christian, Mississippi (a record since surpassed by Hurricane Katrina's unimaginable 27.8' storm surge in Pass Christian in 2005.) Camille barreled up the East Coast and dumped prodigious rains of 12 - 20 inches with isolated amounts up to 31" over Virginia and West Virginia, with most of the rain falling in just 3 - 5 hours. The resulting catastrophic flash flooding killed 113 people, bringing Camille's total death toll to 256, making it the 15th deadliest hurricane in U.S. history. But just how strong was Camille at landfall? In NHC's original historical database, Camille was assumed to have become a Category 5 storm in the southern Gulf of Mexico, with steadily intensification occurring during the final 24 hours before landfall. This database had Camille making landfall with 190 mph winds, tying the storm with Super Typhoon Haiyan (in 2013 in the Philippines) for the strongest winds at landfall of any tropical cyclone in recorded history. However, Camille's landfall intensity was based on visual observations of the sea state from a hurricane hunter aircraft--a technique that is very inexact. Furthermore, comparison with other Category 5 hurricanes called into question Camille's assumed intensity during this final 24-hour period. So, just how strong was Camille?


Figure 1. Hurricane Camille as seen on Sunday, August 17, 1969, about eight hours before making landfall on the Mississippi coast. At the time, Camille was a peak-strength Category 5 storm with 175 mph winds. Image credit: NOAA/NCDC.

Thanks to a reanalysis effort by Margie Kieper of Florida International University and Chris Landsea and Jack Beven of NHC, published last week in the Bulletin of the American Meteorological Society, Camille has now been officially downgraded to 175 mph winds at landfall. The re-analysis puts Camille in second place for the strongest landfalling hurricane in U.S. history, behind the Great 1935 Labor Day Hurricane that hit the Florida Keys, which reanalysis showed had 185 mph winds and a central pressure of 892 mb at landfall. (The only other Category 5 hurricanes on record to hit the U.S. were 1992's Hurricane Andrew--165 mph winds and a 922 mb central pressure--and the 1928 “San Felipe” Hurricane in Puerto Rico--160 mph winds, 931 mb central pressure.) Category 5 hurricanes have maximum sustained winds of 157 mph or greater.


Figure 2. Ships beached by Hurricane Camille's record storm surge in Mississippi. Image credit: NOAA photo library.


Figure 3. The most intense world tropical cyclones at landfall, using the advisories taken from the National Hurricane Center in the Atlantic and Eastern Pacific, and the Joint Typhoon Warning Center (JTWC) for the rest of the world's oceans. Both agencies use 1-minute averaging times for their advisories, as opposed to the 10-minute averaging time used to report wind speeds by most international weather agencies and at most international airports. Note that Super Typhoon Haiyan was originally assessed to have 195 mph winds at landfall by JTWC, but these were reduced to 190 mph after a post-season reanalysis. Also, Hurricane Camille's winds at landfall have also been reduced in a recent reanalysis, from 190 mph to 175 mph.

Revised understanding of a superstorm
The track of Camille had only minor changes due to the re-analysis; the big changes were all to the storm's intensity. Revisions to Camille were accomplished by obtaining the original observations from ships, weather stations, coastal radars, Navy/Air Force/Environmental Science Services Administration (ESSA, now called NOAA) Hurricane Hunter aircraft reconnaissance planes, satellite imagery, and by analyzing Camille based upon our understanding of hurricanes today. The satellite imagery of 1969 was only marginally of use for knowing Camille’s exact position and intensity, because of poor navigation, coarse resolution, and spotty temporal coverage.

Camille is now thought to have reached its peak intensity of 150 knots (175 mph) shortly after a three-day period of steady intensification as the storm moved through the Western Caribbean, crossed the western tip of Cuba, then moved northwards to a position due west of Key West, Florida. As the storm closed in on the Mississippi coast, it is now realized that Camille underwent an eyewall replacement cycle (ERC)--a common occurrence in intense hurricanes whereby the eye of the storm contracts and grows unstable and collapses. The importance of the ERC—the cycle of temporary weakening followed by reintensification as the ERC completes and the new outer eyewall contracts—was not fully understood back in 1969, and would not be until a 1982 paper by Willoughby et al. Camille could no longer support its tiny 11-mile diameter eye when the storm was over the central Gulf of Mexico, and a concentric larger-diameter eye formed around the inner eyewall, resulting in a weakening of the hurricane to a high-end Category 4 storm with 135 knot (155 mph) winds. A hurricane hunter flight during this period reported a clear area that was possibly a moat that separated the inner and outer eyewalls: "Just as we were near the [eye] wall cloud we suddenly broke into a clear area and could see the sea surface below," the copilot, Robert Lee Clark, wrote in 1982. The concentric eyewall structure was also clearly seen on radar images.


Figure 4. WSR-57 radar image of Hurricane Camille from New Orleans at 1732 UTC 17 August 1969. Concentric eyewalls are seen, indicating an eyewall replacement cycle was underway. Check out this impressive 78-frame radar animation of Hurricane Camille's landfall the authors put together as part of the Supplementary Materials for the article. This is probably the earliest radar animation of a hurricane ever constructed.

As Camille approached landfall in Mississippi, the storm apparently was able to recover from the completion of the eyewall replacement cycle, taking advantage of light wind shear and very warm waters to re-intensify to a Category 5 storm with 150 knot (175 mph) winds in the 12 hours before landfall. These winds were concentrated over a small area, about 15 - 20 miles in diameter. According to the paper, "A pressure of 909 mb was measured by Mr. Charles Breath at the onset of the eye in his home just west of the bridge in Bay St. Louis, Mississippi, which was about 3 - 4 miles east of the landfall point. This marine aneroid barometer was subsequently tested and determined to be accurately calibrated. The 909-mb value had been the accepted central pressure value at landfall….However, Mr. Breath also measured a 904-mb pressure at a later point in the eye passage a short distance west of the first measurement….Given that the 904-mb pressure reading was taken near the eastern edge of the eye, a 900-mb central pressure is analyzed at landfall." In an email, lead author Margie Kieper told me: "In providing portions of the interview with Charles Breath Jr, I particularly wanted to show his understanding of barometric pressure, how it related to the intensity of the storm, how important it was to keep the barometer calibrated, and his reaction upon seeing it drop dramatically when Camille's eye approached.  I wanted to show the authenticity that gave to the readings--how similar his understanding was to that of a meteorologist."


Figure 5. The Breath home in in Bay St. Louis, Mississippi three days after Camille, August 20, 1969. Camille's lowest landfall pressure of 904 mb was measured by Mr. Charles Breath at this home. Workers are seen moving surge debris and replacing the roof--minus the Queen Anne dormer that was blown off. Photo courtesy of the Hancock County Historical Society, Bay Saint Louis, MS and the Bulletin of the American Meteorological Society.

Camille a rare hurricane that intensified up until a Gulf Coast landfall
While the re-analysis showed that Camille was not as strong at landfall as originally thought, it did strengthen from a Category 4 storm with 155 mph winds to a Category 5 storm with 175 mph winds in the twelve hours before landfall. This behavior contrasts with many other major hurricanes that have made landfall along the northern Gulf Coast, which weakened prior to landfall. The paper notes that "All 11 hurricanes—most notably Hurricane Katrina in 2005—during the period from 1985 to 2005 having a central pressure less than 973 mb 12 h before landfall in the northern Gulf of Mexico weakened during these last 12 h (Rappaport et al. 2010)." While the paper does not go into the reasons why Camille showed this unique behavior, I speculate that it was because of the storm's relatively small size, which meant that the storm was not able to suck in a large amount of air pollution particles from the Gulf Coast prior to landfall. Hurricanes that approach land are prone to weakening if they pull in large amounts of air pollution particles, which invigorate thunderstorms in the outer spiral bands, causing heavy rain that drags down cold air from aloft to the surface, creating pools of cold air near the surface that act to block the inflow of warm, moist air into the hurricane's core, thus weakening the storm. A 2015 post of mine, Air Pollution and Dust Credited With Weakening Hurricanes Irene and Katrina, describes the process in more detail.

Kudos to Margie Kieper
The first author of the paper, Margie Kieper, is a name long-time readers of this blog will recognize. Margie got her start in hurricane science thanks to this blog and Hurricane Katrina, whose storm surge she analyzed in a series of articles that appear in our storm surge pages. At my encouragement, Margie gave up her career in database management and enrolled in Ph.D. school in Tropical Meteorology at Florida International University three years ago. She has completed her prelims, and is working on her thesis project. The Hurricane Camille re-analysis paper showcases her thorough research methodology--Margie found a large amount of data on Camille that had previously been unknown, and doggedly slogged though the material to come up with what should be the authoritative final scientific analysis of the storm's track and intensity.

Jeff Masters