Super Typhoon Dujuan Slams Taiwan

Super Typhoon Dujuan slammed into eastern Taiwan today as a category-4 typhoon, with maximum sustained winds of approximately 225 KPH / 140 MPH (Met Office 2015). Dujuan made landfall slightly after 0900UTC or 1900 local time.

Dejuan's impressive size and structure was evident in this visible satellite image taken as the sun rose on Monday morning.

Source: @DanLindsey77

Radar and satellite loops depicted a large, powerful typhoon, which dumped tremendous rainfall on this mountainous island. As with other islands in the region, mudslides will be a major threat as heavy rains try to run off the steep terrain.

Most impacts from this storm appear to be from intense winds and heavy rain so far. Storm surge levels on Taiwan tend to be suppressed because the bathymetry, or offshore water depth, is deep, which does not allow water to pile up as efficiently. Also, Taiwan does not have as many defined bays and inlets as the Philippines, so water does not get funneled or trapped as efficiently.

Dujuan generated large waves on Taiwan's east coast

Source: @EarthUncutTV

Although typhoons tend to generate modest storm surge levels on Taiwan, wave heights along the coast are often tremendous. This occurs because waves “feel the bottom” of the ocean and break their energy when they reach shallow coastal waters. On islands with deep bathymetry (and usually high mountains), like Taiwan and Hawaii, most of this wave energy remains intact until the waves are striking the shore.

Dejuan generated massive waves that slammed into sea walls on Taiwan's east coast

Source: http://m.appledaily.com.tw/realtimenews/article/new/20150928/700495/

Typhoon Doug in 1994 provides a good example of a super typhoon that generated moderate surge levels but massive waves on Taiwan. Doug produced a maximum storm surge of 1.5 – 3.0 m (5 – 10 ft) near Lungtung Harbor, but wave heights reached 20 m (66 ft) (Wang et al. 2005).

Typhoon Doug (1994) track and intensity. 

REFERENCES:

 Met Office, 2015: See http://search.metoffice.gov.uk/kb5/metoffice/metoffice/results.page?qt=dujuan&button=Search.

Wang, Y.H., I.H. Lee, D.P. Wang, 2005: Typhoon induced extreme coastal surge: A case study at northeast Taiwan in 1994, Journal of Coastal Research, 21, 548-552.

50-year Anniversary of Hurricane Betsy's Louisiana Storm Surge

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Hurricane Betsy struck South Louisiana 50 years ago today. Betsy made landfall south of New Orleans, near Grand Isle. As Betsy was tracking to the northwest, much of Southeast Louisiana, including St. Bernard and Plaqumines parishes, the New Orleans metro area, and all of Lake Pontchartrain, stayed on the “strong” side of the storm.

Hurricane Betsy inflicted intense winds and high storm surge on Southeast Louisiana. Betsy's storm surge flooded much of eastern and southeastern metro New Orleans.

Image: Wikipedia Commons

Betsy made landfall in the hours before midnight as a category-3 hurricane with maximum sustained winds of approximately 120 mph.  However, just several hours before landfall, Betsy was a category-4 hurricane, near the threshold of category-5, with maximum sustained of 155 mph (Atlantic Oceanographic and Meteorological Laboratory 2014).  Betsy’s intense pre-landfall winds were one reason the storm produced such high storm surge levels in South Louisiana, as storm surge heights correlate better with pre-landfall hurricane winds than wind speeds at landfall (Needham and Keim 2014).

Betsy’s highest storm tide (storm surge + tides) reached 15.7 feet above Mean Sea Level (MSL) at Bohemia- East Landside, in South Louisiana (U.S. Army Corps of Engineers 1965). This observation came from the near the levee on the east side of the Mississippi River, in Plaquemines Parish, about 30 miles upriver from the mouth of the Mississippi.

 Betsy's storm surge in Louisiana peaked at 15.7 ft above Mean Sea Level at Bohemia, in Plaquemine's Parish.

Betsy’s storm surge inundated much of eastern and southeastern metro New Orleans. This flooding unfortunately inflicted both loss of life and tremendous financial losses. Betsy inflicted 75 fatalities (not all in SE Louisiana), and $1.42 billion in property loss (Blake et al. 2011). This made Betsy the first hurricane to produced more than $1 billion in financial losses (Blake et al. 2011).

ADCIRC run of Betsy's peak storm tide levels in South Louisiana. Note the several distinct pockets of water levels exceeding 10 ft (3 m), visible to the east of the Mississippi River levee, in the eastern portion of New Orleans, and in the western portion of Lake Pontchartrain. Also note the drastic difference in surge heights to E and W of MS River.

Image courtesy of J. Westerink, see: http://www3.nd.edu/~adcirc/betsy.htm

Although storm surge flooding in New Orleans caused the biggest impact and attracted the most media attention, Betsy actually inundated much of Southeast Louisiana with a storm tide ranging from 12-16 ft. The map below, which depicts storm surge and storm tide heights, as well as Betsy’s hourly track and intensity, depicts many “red” water levels in the region. In this map, red symbols depict storm surge or storm tide heights between 12-16 ft.

Hurricane Betsy hourly track, intensity and storm surge/ storm tide observation map.

Image courtesy: Hal Needham (SCIPP/ SURGEDAT)

Many people are surprised to learn that Betsy produced the highest storm tide on record near Frenier, on the southwest coast of Lake Pontchartrain. Betsy’s 13.1-ft storm tide at Bonne Carre (a few miles from Frenier) was the highest hurricane-induced water level ever recorded near that location. The 1915 Hurricane produced a 13-ft storm tide near Frenier (Rank #2), but Hurricane Katrina’s storm tide was only 5.58 ft above NAVD88, which is ranked #9 for that location. These data are provided courtesy of the SURGEDAT project, which has compiled a history of 27 high water marks that have been observed at Frenier since 1900.

Betsy generated the highest recorded storm tide level near Frenier, Louisiana. Note that Hurricane Katrina generated the ninth-highest storm tide level in this location.

Image: Hal Needham

This may surprise us, as Frenier is situated on Lake Pontchartrain, and not far from New Orleans, which was devastated from Katrina. This is further proof that storm surge is a very localized phenomenon. While Katrina generated a massive storm surge east of the Mississippi River, in Mississippi Sound, and to the east and north of New Orleans, the wind setup in Lake Pontchartrain did not support a prolonged, intense wind from the east, which is needed to pile up a lot of surge near Frenier.

Both Hurricane Betsy and the 1915 Hurricane produced prolong, intense winds blowing from east to west over Lake Pontchartrain, enabling these storms to generate higher surge levels than Katrina in places like Frenier and near Lake Maurepas.

 Frenier is located on the southwest shore of Lake Pontchartrain. This location requires the strongest hurricane winds to blow from the east or northeast to pile up large storm surges. This happened in Betsy (1965) and during an unnamed hurricane (1915). This did not happen so efficiently during Katrina (2005), keeping storm tide levels < 6 ft (1.83m).

Anecdotal stories from Hurricane Betsy are common in South Louisiana, as Betsy was the measuring stick by which people compared other storms, until Katrina.

A woman who installed a glass elevator on her home near Boothville, Louisiana, once told me that Betsy, Camille and Katrina floated her home from its foundation, but she has rebuilt each time.

 Betsy revealed the vulnerability of communities in eastern and southeastern metro New Orleans to storm surge flooding. This photo was provided by a website that archived the storm damage in Chalmette, St. Bernard Parish.

Image: http://chalmettecoc.org/images/betsy/phpslideshow.php?directory=.&currentPic=0.

My father-in-law tells a story about how he saw the eye of Hurricane Betsy pass over Port Allen, in the early hours of September 10, 1965. Port Allen is just across the river from Baton Rouge, where I work.

But my favorite story comes from Malcolm Moreau, a seasoned weather observer, who has been taking daily rainfall observations for more than 50 years. “Ole Moe” and I worked together in the Southern Regional Climate Center (SRCC) for the past four years, until he retired this summer, less than two months before turning 80 years old. Moe tells the story of how he was working at the National Weather “Bureau” (before it was called the National Weather Service) office in New Orleans the night that Betsy made landfall. Unfortunately, there were problems with some of the equipment on the roof of the building, and Moe was chosen to go on the roof for a maintenance job at the height of the storm! He still recounts how his coworkers tied a rope to him and held him fast from the stairwell, so he wouldn’t blow away!

Betsy stories abound in Louisiana because many eyewitnesses are still alive to recount the tales from this storm, unlike major hurricanes that struck Louisiana in 1893 and 1915. Also, Betsy generated a massive storm surge that produced the highest water levels on record in many places until Hurricane Katrina. It truly became the measuring stick for storm surge potential in Southeast Louisiana for decades, as it produced observed water levels from which the New Orleans metro area tried to protect itself for a long period of time.

REFERENCES:

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Atlantic Oceanographic & Meteorological Laboratory, 2014: Chronological list of all hurricanes:1851-2014. Funded by the National Oceanic and Atmospheric Administration. Link:http://www.aoml.noaa.gov/hrd/hurdat/All_U.S._Hurricanes.html.

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Blake, E.S., C.W. Landsea, and E.J. Gibney, 2011: The Deadliest, Costliest, and Most Intense United States Tropical Cyclones from 1851 to 2010 (And Other Frequently Requested Hurricane Facts), NOAA Technical Memorandum NWS NHC-6, available on the Web at: http://www.nhc.noaa.gov/pdf/nws-nhc-6.pdf.

Needham, H.F., and B.D. Keim, 2014: Correlating Storm Surge Heights with Tropical Cyclone Winds at and before Landfall, Earth Interactions, 18, 1-26.

U.S. Army Corps of Engineers, 1965: Report on Hurricane Betsy, 8-11 September, 1965. New Orleans District Office.

Surges That Will Shock You- Global Surge Highlights from August, 2015

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Global Storm Surge Highlights

August 2015

The month of August, 2015, was an active month in the tropics, particularly in the Northeast and Northwest Pacific Ocean. This month, however, witnessed surprising surges in places like the Cape Verde Islands (tropical) and coastal Chile (non-tropical).

A massive non-tropical coastal flood in Chile, on August 8, produced tremendous waves that slammed cars and buildings.

Image and video: @MeteoAste on Twitter.

TROPICAL SURGES

1. Super Typhoon Soudelor

Super Typhoon Soudelor intensified into a category-5 equivalent cyclone with maximum sustained 1-min winds reaching 180 MPH (285 KPH), according to the Joint Typhoon Warning Center. Fortunately, this super typhoon weakened to a category-3 equivalent cyclone, before making landfall in Taiwan, in the early morning of August 8.

Souledor also made a direct strike on Saipan, in the Northern Mariana Islands, and the remnants of this powerful super typhoon flooded China.

Super Typhoon Soudelor made a direct strike on Taiwan on the morning of Aug 8, as a category-3 equivalent cyclone. Tracking Map: Unisys Corporation.

As is common with super typhoons in the Western North Pacific, storm surge levels were modest, but wave heights were tremendous. Such waves often take people by surprise, as in the unfortunate case when a powerful wave from Soudelor swept a woman and her daughter out to sea on the Taiwanese coast (Associated Press 2015).

2. Hurricanes Near Hawaii

August has been a very active month in the Eastern North Pacific. During this month, several hurricanes approached Hawaii, however, none made direct landfall. However, hurricanes Guillermo, Hilda, Kilo and Ignacio all generated high surf on the islands.

As August came to a close, three active hurricanes were centered over the Eastern North Pacific Ocean. These cyclones, especially Ignacio, generated large waves that pounded the Hawaiian Islands. 

Labeled Image: Hal Needham; Base Map with Cyclones: http://earth.nullschool.net/.

3. Typhoon Goni

Typhoon Goni was a powerful cyclone that tracked from east to west, before nearly stalling off the coast of Luzon, in the northern Philippines. Unfortunately, Goni’s surge and high waves pounded the northern Philippines, as the storm stalled off the coast. The typhoon then picked up forward speed and tracked north, putting the islands of Southern Japan, like Okinawa, in the strong sector of this storm. Goni generated storm surge and damaging waves along these islands, as well as mainland Japan, where it made landfall on Aug 25.

Typhoon Goni generated massive waves that slammed into the Philippines and Japan. This image from OneIndia News shows a massive wave crashing into the Japanese coast.

Link: https://www.youtube.com/watch?v=FYXyjatTr1Y.

4. Hurricane Fred

Hurricane Fred rapidly intensified into a hurricane while approaching the Cape Verde Islands, off the coast of West Africa. It is rare for a hurricane to develop so far east, and this was the first direct strike from a hurricane in the Cape Verde Islands since 1892 (Masters and Henson 2015).

Video and photos coming from the Cape Verde Islands reveal that Fred did produce a coastal flood event.  A video posted by @zenaidamz on Twitter shows still water inundation (water level above ground) of perhaps 1.5 ft (0.46 m) at a coastal resort on the Island of Sal.

Hurricane Fred inundated this resort, on the Island of Sal, with approximately 1.5 feet (0.46 m) of water.

Video posted by @zenaidamz on Twitter.

NON-TROPICAL SURGES

1. An extraordinarily powerful coastal flood event slammed Chile’s west coast on August 8. A combination of moderate storm surge and massive waves pounded the coast at Avenida Peru, Vina del Mar, in the region of Valparaiso. Photos and videos of this surge event show waves slamming into cars and buildings.

 A wave slams into cars on Avenida Peru, Vina del Mar, Valparaiso, Chile, in the Aug 8 coastal flood event.

Image/ video source: @MeteoAste on Twitter.

REFERENCES

Associated Press, 2015: Typhoon Threatens China After 10 Dead or Missing in Taiwan. The New York Times, August 7, 2015. Link: http://www.nytimes.com/aponline/2015/08/07/world/asia/ap-as-asia-typhoon.html?_r=1.

Masters, J., and B. Henson, 2015: Rare Hurricane Pounds Cape Verde Islands. Weather Underground blog post from August 31, 2015. Link: http://www.wunderground.com/blog/JeffMasters/comment.html?entrynum=3097.

A Rare Tropical Surge Strikes Cape Verde Islands

This morning, Hurricane Fred was centered in the midst of the Cape Verde Island chain, off the west coast of Africa. Fred's sustained winds were estimated at 80 MPH (129 KPH). Typically, hurricanes form farther west in the Atlantic, as tropical waves (atmospheric waves, not oceanic) move from east to west off the coast of Africa.

Hurricane Fred has quickly intensified to a category-1 hurricane centered in the midst of the Cape Verde Islands. At this time, Fred's maximum sustained winds are estimated at 80 MPH (129 KPH).
Image: http://www.ssd.noaa.gov/PS/TROP/floaters/06L/imagery/rgb0.gif

Fred is pushing sea water onto the islands. The webcam at Santa Maria, near the southern tip of the island of Sal, shows large waves and storm surge pushing water onto the beach.

 

Fred's storm surge was beginning to inundate the beach at Santa Maria, on the Cape Verde island of Sal. 

Webcam source: http://www.capeverde.com/live-webcams/sal-pontao-zoom.html

If you're a physical geography buff, with an interest in the coast, it is clear that Fred's storm surge is pushing water past the typical swash zone, and the runnels are filling with water. At this time the ridge, or swash bar, at Santa Maria, is not yet inundated. A few boats are resting on the swash bar, and we can only wonder if Fred's surge will eventually wash them off. (See graphic below for beach profile that shows the location of runnels and swash bar.)

 Physical profile of a sandy beach. Fred's storm surge is pushing water past the typical swash zone and filling runnels with sea water. At Santa Maria the swash bar appears wet but not inundated at this time.  

Image: http://classconnection.s3.amazonaws.com/114/flashcards/1546114/png/beach1337143672563.png

The total storm tide (surge + tide) at this location may be around 2 ft (0.61 m) above Mean Sea Level (MSL), but that's just an estimate. Sometimes high waves cause additional flooding from a process called "wave runup," in which the water from wave #1 has not yet retreated before the water from wave #2 arrives. In such cases, even a small storm tide of 1-2 feet can start inundating low-lying areas because of the additional water provided by the waves.

As Fred has intensified pretty quickly from a tropical wave to a tropical storm and then a hurricane, we should not expect excessive storm surges on the Cape Verde Islands. It takes awhile for hurricanes to displace sea water, and Fred's 12 MPH (19 KPH) forward speed should move it past the islands before it has a chance to generate surges exceeding 3 or 4 feet.

Why It's Misleading to Label Katrina as a "Category-3" Hurricane

Hurricane Katrina is often referred to as a "category 3" hurricane. I want to make the case that this label is misleading.

Precisely 10 years ago this morning, Hurricane Katrina made landfall in Louisiana and Mississippi as a category-3 hurricane on the Saffir-Simpson Scale. The first landfall along the Northern Gulf Coast occurred just after 6AM CDT near Buras, Louisiana, where maximum sustained winds were estimated at 110 kts (127 MPH) (Knabb et al. 2011). Katrina then tracked across shallow water and wetlands before making a final landfall near the Louisiana/ Mississippi border, with maximum sustained winds around 105 kts (121 MPH) (Knabb et al. 2011).

 Although Katrina is often referred to as a "category-3" hurricane, referring to its maximum sustained wind speed at landfall, it generated a massive storm surge that flooded approximately 80% of metro New Orleans.  
Image: http://i.dailymail.co.uk/i/pix/2012/08/28/article-2193403-05488FCE0000044D-642_964x642.jpg.

Both of these intensities are classified as category-3 winds on the Saffir-Simpson Scale.

However, Katrina generated a 27.8 ft (8.47 m) storm surge at Pass Christian, Mississippi (Knabb et al. 2011), which is the highest surge in the history of the Western Hemisphere (Needham et al. 2015). The surge in St. Bernard Parish, Louisiana, topped out at 18.7 ft (Knabb et al. 2011), which is the highest surge level in the modern history of Louisiana (Needham et al. 2013). This storm surge was responsible for flooding approximately 80% of metro New Orleans (Kates et al. 2006) and led to a catastrophe in which more than 1800 lives were lost (McTaggart-Cowan et al. 2008). The storm surge directly caused between 600-700 of these deaths (Boyd 2011). Katrina’s price tag totaled more than $100 billion (Blake et al. 2011), making it the most costly natural disaster in U.S. history (Kessler et al. 2006; Baade et al. 2007).

Katrina's rapidly rising flood waters trapped thousands of people on roofs and attics in the metro New Orleans area. These flood waters directly claimed more than 600 fatalities.  
Image: https://media.epactnetwork.com/wp-content/uploads/2013/11/04depa450.jpg.

So how did a “category-3” hurricane generate such a terrible catastrophe?

Fortunately, since Hurricane Katrina, much research has investigated the complex nature of storm surge, helping us understand the complexities of this hazard. The bottom line is that many variables contribute to storm surge height, not the maximum sustained wind speed of a hurricane alone.

Hurricane size, or the area of strong winds, jumped to the forefront, as a variable that was not understood very well preceding Hurricane Katrina. The importance of cyclone size became clear as Katrina generated a higher storm surge than Hurricane Camille of 1969, although Camille produced stronger winds. Katrina’s large size played an important role in this process, as the diameter of hurricane force winds extended over 210 miles of open water and tropical storm force winds extended over 460 miles of open water as the sun set on Katrina the night before landfall (Knabb et al. 2011). This tremendously large wind field displaced a massive amount of water that piled up on the Louisiana and Mississippi coasts.

 As the sun set on Hurricane Katrina on Sunday, August 28, 2005, the storm was centered 130 miles S of the Mouth of the Mississippi River. Maximum sustained winds exceeded 160MPH, the diameter of hurricane force winds extended for 210 miles and tropical storm force winds extended across a diameter of 460 miles. Image: NOAA.

Some notable papers in the past 10 years that investigated the role of hurricane size for generating storm surge include Irish et al. (2008); Nielsen (2009); and Dietrich et al. (2011).

Several hurricanes following Katrina also taught us about the importance of hurricane size for generating storm surge. In 2008, Hurricane Ike made landfall along the Texas Coast as a category-2 hurricane, but generated a storm surge of 17.5 ft (5.33 m) in Chambers County, Texas. (Berg 2010). Ike also inundated much of South Louisiana with a storm surge that exceeded 11.5 ft (3.5 m) and extended inland for more than 33 miles (55 km) (Federal Emergency Management Agency 2008). In 2012, Hurricane Isaac made landfall as a category-1 hurricane in South Louisiana, but generated a storm surge that exceeded 14 ft  (4.3 m) (McCallum et al. 2012). Later that year, Hurricane Sandy approached the coastline of New Jersey as a category-1 hurricane, but generated a massive storm surge that inundated New Jersey and New York with seawater, inflicting a price tag of more than $50 billion and contributing to 147 fatalities (Blake et al. 2013).

 

In 2012, Hurricane Isaac's large size enabled it to inundate Long Beach, Mississippi (above), although the storm was a category-1 hurricane that made landfall south of New Orleans. 

Image: http://www.baynews9.com/content/dam/news/images/2012/08/Long-Beach-MS-082912.jpg.

  

Hurricanes Ike, Isaac and Sandy were not officially classified as “major” hurricanes, because they made landfall with wind speeds less than the category-3 threshold. However, they collectively generated more than $60 billion in damage (Blake et al. 2011), primarily from large, destructive storm surges. All three of these hurricanes were geographically large, enabling them to generate massive surges.

Hurricane forward speed is another variable that influences surge timing and height. This role of this variable was investigated by (Rego and Li 2009). Hurricane Isaac provides a classic example of the increased surge potential from slow-moving hurricanes. Isaac’s forward motion became nearly stationary along the South Louisiana coast, enabling the storm to push water into Southeast Louisiana, Lake Pontchartrain and Mississippi for an extended period of time.

Other variables that generate storm surge include bathymetry and coastal shape. The influence of bathymetry, or offshore water depth, is a bit counter-intuitive because storm surges tend to reach higher levels in areas with shallow bathymetry (Needham and Keim 2011). If you’ve visited coastal Mississippi you know that the water is so shallow that you can walk offshore 150 feet (~45 meters) and the water will not even be as deep as your knee in some places. The influence of harbors and bays are also counterintuitive, as they typically provide a safe haven for boats and ships, but during a hurricane-generated storm surge actually enhance surge heights (Needham and Keim 2011).

 A 25.1-ft (7.65-m) rod does not quite reach the height of tree bark removal on East Ship Island, Mississippi, following Hurricane Katrina. The tree bark removal at this site extended to 8.2 m (26.9 ft), indicating an extraordinarily high storm surge at this location. Katrina's surge in Mississippi was the highest surge level in the modern history of the Western Hemisphere. Photo provided by Hermann Fritz.

Two overlooked variables for storm surge generation are the roles of pre-landfall wind speed and size. Jordan and Clayson (2008) first investigated this topic, and several years later I wrote companion papers with Dr. Barry Keim that provided the first data-driven analysis of this phenomenon for the U.S. Gulf Coast region (Needham and Keim 2014a; Needham and Keim 2014b). These analyses quantified the improved correlation of storm surge heights with pre-landfall wind speeds and size, compared to winds and size at landfall.

The graphic below shows the correlation between storm surge height and maximum sustained winds at landfall and at 3-hour increments preceding landfall. The blue bars represent the correlation using an array, or list, of actual wind speeds. The red bars indicate the improved correlation levels when that array of wind speeds is raised to the optimal exponential power. This graphic is adapted from Needham and Keim (2014a).

Needham and Keim (2014a) found that storm surge heights correlate better with wind speeds 18 hours before landfall than any other time period. Graphic adapted from Needham and Keim (2014a).

This graphic shows that storm surge heights and winds have the poorest correlation at landfall, but that correlation dramatically improves as we use the wind speed before landfall. The relationship is optimal at 18 hours before landfall, when the R-squared value approaches 0.70, if the array of wind speeds is raised to the power of 2.2. This analysis reveals that the relationship between surge heights and wind speed is quite non-linear; we found that doubling the strength of pre-landfall winds increases the surge potential by a factor of around 4.60.

Hurricane Katrina was a very large and intense tropical cyclone 18 hours before its final landfall. The maximum sustained winds at that time exceeded 170 MPH (Elsner and Jagger 2013), which would have placed this storm on the threshold of a category-6 hurricane, if the Saffir-Simpson scale were a continuous scale. In fact, Hurricane Katrina’s pre-landfall wind speed was comparable to Camille’s. Katrina’s wind at this time was only about 11 kts, or 13 mph, weaker than Camille’s (at the same time increment) (Elsner and Jagger 2013), but Katrina’s larger size enabled it to generate a higher surge.

 Map of Hurricane Katrina's hourly position and intensity, as well as the height of storm surge and storm tide observations. Katrina was a large, cat-5 hurricane before striking Louisiana and Mississippi. Storm surge and storm tide heights exceeded 16-ft (4.88 m) along the entire Mississippi Coast and portions of SE Louisiana. 
Map archive at: http://surge.srcc.lsu.edu/historical_maps.html.

So we must be careful when we refer to Katrina as a “cat-3” hurricane.  Katrina’s storm surge caused much more damage and loss of life than its strong winds, and levees are built to protect from water, not wind. To call Katrina a “cat-3” storm uses only one metric- the maximum sustained wind speed at landfall, to classify this cyclone. This label is misleading, as the public is aware that the Saffir-Simpson Scale ranges from 1 to 5 and a “cat-3” sounds like an “average” hurricane to the public. This label may be misused to imply that the flood protection around New Orleans could not withstand a strike from an “average” (cat-3) hurricane, which is very misleading.

In reality, Katrina was a large hurricane, with maximum sustained winds that would have approached category-6, if the Saffir-Simpson Scale were a continuous scale. And those wind speeds peaked around 18 hours before final landfall, the time that correlates best for generating catastrophic surges. Taking into account its large size, as well as the shallow bathymetry and presence of bays (like Bay St. Louis) near it’s final landfall, we should not be surprised that Hurricane Katrina generated the largest storm surge in the modern history of the Western Hemisphere.

Perhaps we should say Katrina struck the Northern Gulf Coast with cat-3 winds and a cat-5 surge? It’s a controversial statement, especially after much effort to disassociate Saffir-Simpson wind speed categories from storm surge heights. Yet, in practice, Katrina is regularly called a "cat-3" hurricane, and on the ground, many people still refer to flood protection as "cat-4" or "cat-3" levees. Calling Katrina a cat-3 (at landfall) wind event and cat-5 surge event, would at least communicate the notion that these storms are more complex than just one number on a scale of 1-5. Either that, or perhaps we should just say it was a hurricane that made landfall as a cat-3, but produced the highest surge in the history of our hemisphere.

REFERENCES

Baade, R.A., R. Baumann, and V. Matheson, 2007: Estimating the economic impact of natural and social disasters, with an application to Hurricane Katrina. Urban Studies, 44, 11, 2061-2976.

Berg, R., 2010: Tropical Cyclone Report, Hurricane Ike. The National Hurricane Center, Miami, Florida, United States. Report available on the Web at: www.nhc.noaa.gov/pdf/TCR-AL092008_Ike_3May10.pdf.

Blake, E.S., C.W. Landsea, and E.J. Gibney, 2011: The Deadliest, Costliest, and Most Intense United States Tropical Cyclones from 1851 to 2010 (And Other Frequently Requested Hurricane Facts). NOAA Technical Memorandum NWS NHC-6. This publication is available on the Web at: http://www.nhc.noaa.gov/pdf/nws-nhc-6.pdf.

Blake, E.S., T.B. Kimberlain, R.J. Berg, J.P. Cangialosi, and J.L. Beven II, 2013: Tropical Cyclone Report, Hurricane Sandy, (AL182012), 22-29 October 2012. National Hurricane Center, Miami, Florida, USA. Available on the Web at: http://www.nhc.noaa.gov/data/tcr/AL182012_Sandy.pdf.

Boyd, E., 2011: Fatalities Due to Hurricane Katrina’s Impacts on Louisiana. Dissertation successfully defended April 20, 2011. Louisiana State University Department of Geography and Anthropology, Baton Rouge, Louisiana.

Dietrich, J.C., M. Zijlema, J.J. Westerink, L.H. Holthuijsen, C. Dawson, R. A. Luettich, Jr., R. Jensen, J.M. Smith, G.S. Stelling, and G.W. Stone, 2011: Modeling Hurricane Waves and Storm Surge using Integrally-Coupled, Scalable Computations. Coastal Engineering, 58, 45-65.

Elsner, J.B., and T.H. Jagger, 2013: Hurricane Climatology: A Modern Statistical Guide Using R. Oxford University Press, New York, USA. 430 pp.

Federal Emergency Management Agency, 2008: Hurricane Ike in Texas and Louisiana. Mitigation Assessment Team Report. Available on the web at: http://www.fema.gov/library/file?type=publishedFile&file=757_ape_final.pdf&fileid=71147ed0-b6a2-11df-97ce-001cc4568fb6.

Irish, J.L., D.T. Resio, and J.J. Ratcliff, 2008: The Influence of Storm Size on Hurricane Surge. Journal of Physical Oceanography, 38, 2003-2013.

Jordan, II, M.R., and C.A. Clayson, 2008: A new approach to using wind speed for prediction of tropical cyclone generated storm surge. Geophysical Research Letters, 35, doi: 10.1029/2008GL033564.

Kates, R.W., C.E. Colten, S. Laska, and S.P. Leatherman, 2006: Reconstruction of New Orleans after Hurricane Katrina: A research perspective. Proceedings of the National Academy of Sciences of the United States of America, 103, 14653-14660.

Kessler, R.C., S. Galea, R.T. Jones, and H.A. Parker, 2006: Mental illness and suicidality after Hurricane Katrina. Bulletin of the World Health Organization, 84, 12, 930-939.

Knabb, R.D. J.R. Rhome, and D.P. Brown, 2011: Tropical Cyclone Report, Hurricane Katrina, 23-30 August 2005. Report produced by the National Hurricane Center, Miami, Florida, and published on the Web at: http://www.nhc.noaa.gov/pdf/TCR-AL122005_Katrina.pdf.

McCallum, B.E., B.D. McGee, D.R. Kimbrow, M.S. Runner, J.A. Painter, E.R. Frantz, and A.J. Gotvald, 2012: Monitoring Storm Tide Flooding from Hurricane Isaac along the Gulf Coast of the United States, August 2012. Open-File Report 2012-1263. Available on the Web at: http://pubs.usgs.gov/of/2012/1263/.

McTaggart-Cowan R., G.D. Deane, L.F. Bosart, C.A. Davis, T.J. Galarneau, Jr., 2008: Climatology of tropical cyclogenesis in the North Atlantic (1948-2004). Monthly Weather Review, 136, 1284-1304.

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I'm Back!

I'm Back!

After a two-month break from blogging, I'm back! I expect to be on social media frequently during the upcoming months due to several factors:

1. We are approaching the peak of the 2015 Atlantic Hurricane Season.

2. Tropical Storm Erika in the Atlantic and Hurricane Ignacio in the Central Pacific are both forecast to approach U.S. coastlines early next week. It appears that Erika may approach the coast of Florida, Georgia and the Carolinas, while Ignacio approaches the Hawaiian Islands from the Southeast.

TS Erika has shown explosive convection in the Eastern Caribbean during the past 12 hours. If the system can maintain organization for the next 48 hours, it will likely enter a more favorable environment and strengthen.

3. Saturday, August 29, is the 10-year anniversary of Hurricane Katrina's landfall in Louisiana and Mississippi. Many events in these states are commemorating the anniversary of this historic storm. I will be giving a talk at the Katrina and Rita Symposium at LSU on Fri Aug 28, along with colleagues Barry Keim, Craig Colten and Amanda Lewis.

Here is a link to the program: http://sites01.lsu.edu/wp/ored/katrina-10/.

The Katrina & Rita Symposium will be held at the LSU Digital Media Center from 9AM- 5PM on Fri Aug 28.

4. Climate Central has expressed interest in helping me reach a wider audience. This will be an excellent partnership, as Climate Central has a great reputation in the climate science community and focuses a lot of attention on education and outreach. Some of that content will parallel updates on this blog.

Catching Up

This year has been really busy here at LSU! NOAA's SCIPP RISA program, which funds my work, values stakeholder-driven research. So over the past several months I have done a combination of research and outreach. Here are some highlights:

1. In May I participated in a Coastal Tools Cafe in St. Petersburg, Florida, organized by the Gulf of Mexico Alliance. I also presented storm surge research to a group of Florida educators.

2. In June I gave a storm surge presentation to a group of visiting scientists from the Caribbean region. Their program was sponsored by USAID.

3. Earlier this year I worked with co-authors Barry Keim and David Sathiaraj to complete revisions on a massive publication that was published in June in Reviews of Geophysics. The paper titled, "A Review of Tropical Cyclone-Generated Storm Surges: Global Data Sources, Observations and Impacts," provides an overview of global storm surge observations and impacts, while documenting the creation of SURGEDAT, a global storm surge database.

Link: http://onlinelibrary.wiley.com/doi/10.1002/2014RG000477/full

Our paper in Reviews of Geophysics provides an overview of tropical cyclone-generated storm surges around the world, as well as the creation of a global storm surge database.

4. The SCIPP and SECC RISA programs have collaborated to improve storm surge data for Florida and the Southeast US Coast. I have also worked closely with students at LSU to improve Gulf Coast surge data. We added more than 200 new observations to SURGEDAT that came completely from raw tide gauge data. We are now analyzing these data for several papers.

Hurricane Gustav (2008) generated a storm surge (difference between green and blue lines) exceeding 4 ft at Grand Isle, LA. I worked with a team of students to extract raw surge data and add these obs to SURGEDAT. This process added more than 200 new observations to the SURGEDAT database along the U.S. Gulf Coast. Source: NOAA Tides and Currents

Anyway, it's great to be back! I'm looking forward to jumping back into social media and interacting with many of you during the second half of the Atlantic Hurricane Season!