Tuesday, November 12, 2013

Sudden Shift in Wind Direction Caused Wall of Water to Slam into Tacloban, Philippines




A massive storm surge, described by many as a wall of water, slammed the Philippines as Super Typhoon Haiyan came ashore last week. The powerful surge deposited large ships in neighborhoods.
Image: Noel Celis/ AFP/ Getty Images

A sudden shift in the wind direction caused a wall of sea water to crash into Philippine city of Tacloban last Friday. This wall of water obliterated entire neighborhoods, and may have killed thousands of people.

At a given location, intense cyclonic winds may quickly change direction because winds in tropical cyclones spiral around the placid eye. The most intense winds are generally found in the eye wall, a ring of intense wind and storms that surrounds the eye of a cyclone.

As Tropical Cyclone Haiyan approached the city of Tacloban, very strong winds blew from the north across San Pedro and San Pablo Bay, the body of water on which Tacloban is located. Intense winds from this direction would have tempered or even reduced water levels in the Bay. The satellite image below depicts the storm location relative to Tacloban as the eye approached the city from the east.


Intense northerly winds tempered the surge levels near the city of Tacloban when Super Typhoon Haiyan was centered to the east of the city.
Satellite Image: CIMSS/ SSEC/ Univ of Wisconsin- Madison


However, as the center of the cyclone tracked from east to west, passing south of the city, the wind direction near Tacloban shifted, and the most intense tropical cyclone winds ever felt on land pushed a massive wall of water towards the city. The satellite image below, taken just one hour after the first image, shows the storm’s position at this time. Interpretation of these images reveals that the shift in winds, and the sudden surge of waters, happened extremely fast, as the winds continued to blow from the north near Tacloban for some time after the first image was taken.

As Haiyan's center of circulation moved west, the winds near Tacloban suddenly shifted to the southeast. This rapid shift in wind direction caused a wall of water to blow into the city. This image was taken only one hour after the first image.
Satellite Image: CIMSS/ SSEC/ Univ of Wisconsin- Madison


The sudden shift in winds caused a massive wall of water to slam into the north end of the Bay, including the city of Tacloban. Although storm surge is often described as a dome of high water, eyewitnesses described this surge as a wall of water that washed away everything in its path.

The ingredients that led to this quick-moving wall of water were also present during the 1900 Galveston Hurricane, which killed between 6,000 and 8,000 people (Rappaport and Fernandez-Partagas 1995) in the deadliest natural disaster in U.S. history.  As the hurricane approached Galveston, intense winds were blowing offshore, which helped temper the height of the storm surge. However, as the eye of the storm approached the city, the wind direction shifted and the water rose very rapidly.

A sudden shift in wind direction enabled a 6.1 m (20 ft) surge to rapidly move into Galveston, Texas, in the most deadly natural disaster in U.S. history.

Isaac Cline, the Chief Meteorologist at Galveston, witnessed this rapid water rise first hand, while standing in his home. Although he did not describe the surge as a wall of water, he estimated the water rose four feet (1.22 m) in four seconds. The surge continued to rise, reaching a height of 6.1 meters (20 feet) (Garriott 1900).

Quote from Isaac Cline:
The water rose at a steady rate from 3 p.m. until about 7:30 p.m., when there was a sudden rise of about four feet in as many seconds. I was standing at my front door, which was partly open, watching the water, which was flowing with great rapidity from east to west. The water at this time was about eight inches deep in my residence, and the sudden rise of 4 feet brought it above my waist before I could change my position.

(National Oceanic and Atmospheric Administration 2004).

 Isaac Cline, the Chief Meteorologist at Galveston, Texas, observed a four foot (1.22 m) rise in water level in four seconds during the 1900 Galveston Hurricane.
Image: http://www.awesomestories.com/assets/isaac-cline1

Although there are many differences between the Galveston Hurricane of 1900 and Super Typhoon Haiyan, the shift in wind direction, rapid water rise, and massive amount of fatalities are similar. Such comparisons reveal the value of shared knowledge regarding storm surge inundations, which have emerged as one of the world’s foremost hazards.

Researchers with the Southern Climate Impact Planning Program (SCIPP) at Louisiana State University and the University of Oklahoma have partnered to build a global storm surge database that enables such comparisons. The database, called SURGEDAT, has archived the location and height of peak storm surge for more than 650 global surge events since 1880. The database can be found on the web at: http://surge.srcc.lsu.edu.

Although SURGEDAT has archived 113 surge events in East Asia, data from the Philippines and other countries are still being built and will be uploaded to the website this winter. For the most recent surge data, please contact Hal Needham by email at the following address: hal"at"srcc.lsu.edu.


 SURGEDAT has identified the location and height of peak storm surge for more than 650 tropical cyclones around the world since 1880. Recent work from East Asia, including the Philippines, will be uploaded this winter. Link: http://surge.srcc.lsu.edu.



References

Garriott, E.B., 1900: West Indian hurricane of September 1-12, 1900. Monthly Weather Review, 28, 371-378.

National Oceanic and Atmospheric Administration, 2004: NOAA History, A Science Odyssey. Galveston Storm of 1900. Available on the Web at: http://www.history.noaa.gov/stories_tales/cline2.html.

Rappaport, E.N, and J. Fernandez-Partagas, 1995: The deadliest Atlantic tropical cyclones, 1492-1994. NOAA Technical Memorandum NWS NHC-47, National Hurricane Center, Pgs. 1-41.

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