Friday, April 11, 2014

Comparing Ita's Storm Surge to Typhoon Haiyan

Several people have asked me to compare the storm surge from Tropical Cyclone Ita to Typhoon Haiyan. Ita made landfall today along the coast of Queensland, Australia, north of Cooktown, while Typhoon Haiyan produced a devastating storm surge in the Philippines last November.

Infrared satellite image of Severe Tropical Cyclone Ita as it made landfall near Cape Flattery, Queensland, Australia, around 9PM Australia EST on Friday, April 11, 2014


Numerous factors influence the generation of storm surge in a tropical cyclone. These factors include "storm" variables, such as the geographic size of the cyclone, maximum sustained winds and forward motion, as well as "non-storm" variables, such as the offshore water depth (bathymetry), coastal shape, and the angle of the storm track compared to the coastal profile.

Both Queensland, Australia and the Philippines have numerous bays that enhance storm surge levels. The Cairns waterfront shown in this photo will be vulnerable to storm surge from Tropical Cyclone Ita. Photo: www.yesaustralia.com.

Haiyan's "storm" variables were among the most severe of any landfalling tropical cyclone in history. This geographically large storm made landfall in the Philippines with maximum sustained winds exceeding 190 MPH (300 KPH), which made it the most intense tropical cyclone in history at landfall. Although Ita was classified as a category-5 tropical cyclone before making landfall in Queensland, the geographic size of this storm and maximum sustained winds were less severe than Haiyan.

However, comparing the "non-storm" (coastal) variables becomes more complicated, and I have not seen any information comparing the coastal profiles of the Philippines vs. Queensland, Australia. Both areas have numerous bays and harbors, which enhance surge levels.


Super Typhoon Haiyan was a large, intense tropical cyclone as it approached the Philippines in November, 2013. This cyclone generated the strongest winds at landfall in history.


The biggest difference between these two storms is that Ita is moving in the direction of onshore winds. The onshore winds are located to the south of the landfall location, and the storm is moving to the southwest. This means that vulnerable locations like Cooktown and Cairns have experienced prolonged onshore winds and will see these onshore winds, and surge levels, gradually increase as the storm center gets closer.

The track of Haiyan was quite different. As Haiyan approached cities like Tacolban, strong winds were blowing offshore, and then after the eye passed the strongest winds blew immediately onshore, generating a massive wall of water that slammed Tacloban, in a coastal flood event that was more typical of a tsunami than a storm surge. In other words, Haiyan's track enabled the strongest winds to suddenly reverse and immediately push water inland, producing a surge that surprised, and killed, many people. Haiyan generated a storm tide of around 6.5 m near the Tacloban Airport.

Super Typhoon Haiyan generated a devastating storm surge to the Philippines in November, 2013. Peak surge levels reached at least 6.5 m near the city of Tacloban. Photo: AP/ Aaron Favila.


Expect Ita's surge to rise more gradually along the Northern Queensland Coast, with highest surge levels from Cairns north. Also, because Ita is forecast to track somewhat parallel to the coast after making landfall, expect an extensive area to observe onshore winds. This means that hundreds of kilometers of coastline with observe strong onshore winds and high storm surge levels. I have not come across specific storm surge or storm tide forecasts for this event.

In summary, this is how Ita will differ from Haiyan:

1) It is difficult to predict the difference in peak surge level between Ita and Haiyan, as I have not seen any specific storm surge forecasts, or comparisons in the coastal profile between Queensland and the Philippines. Both the Philippines and Queensland have many very distinct bays, and we would expect the peak surge levels to be found in the interior portion of these bays.

2) Ita's surge should rise more gradually than Haiyan, and a sudden "tsunami-like wave" should not be expected. Nonetheless, dangerous storm surge will occur along the coast, particularly north of Cairns.

3) Ita's surge will likely flood a much more extensive area of coastline, because hundreds of kilometers of coastline will observed an extended period of onshore winds.

The Australia Bureau of Meteorology will continue posting important updates as this storm surge event unfolds.

30,000 People Urged to Evacuate Cairns, Australia, Due to Storm Surge Threat

In a statement released at 9:11PM Australian Eastern Standard Time, the Australia Bureau of Meteorology reported that Severe Tropical Cyclone Ita was crossing the Queensland Coast near Cape Flattery, with wind gusts reaching 230 km/hr (142 MPH). This makes Ita a dangerous category-4 tropical cyclone.

Severe Tropical Cyclone Ita made landfall shortly after 9:00PM Australian Eastern Standard Time on Friday, April 11. As the system tracks to the southwest and then south, strong winds and destructive storm surge are forecast for cities like Cooktown and Cairns.


A destructive storm surge is expected near and to the south of the landfall location. Cities that will likely be impacted by the surge include Cooktown and Cairns. More than 30,000 people have been urged to evacuate the Cairns area because of storm surge threat. Link: http://www.abc.net.au/news/2014-04-11/cyclone-ita3a-cairns-residents-brace-for-storm-surge/5385256.

Cairns is susceptible to storm surge in this case because the city is located on a harbor that is open to the northeast. The strongest onshore winds from Ita will blow right into the harbor and help funnel high storm surge towards Cairns. Although harbors are typically safe place for marine infrastructure, during tropical cyclones, storm surge levels are typically higher inside harbors than other areas along the open coast.

The harbor at Cairns opens to the northeast, which will enable Ita's strongest winds in this area to funnel water onto the Cairns' waterfront. People along this coastline are at risk from storm surge inundation. Image: www.yesaustralia.com.


A radar loop provided by Brian McNoldy at the University of Miami shows Ita making landfall, and the progression of intense squalls moving south along the Queensland Coast. Link: http://andrew.rsmas.miami.edu/bmcnoldy/tropics/radar/. Surge levels from Cooktown to Cairns should continue to build as Ita tracks to the southwest, then south.

A still image from radar loop shows progression of intense squalls moving south along Queensland Coast. Radar loop provided by Brian McNoldy at: http://andrew.rsmas.miami.edu/bmcnoldy/tropics/radar/. 




Thursday, April 10, 2014

Severe Tropical Cyclone Ita to Produce Massive Storm Surge near World's Highest Historical Surge Site

Severe Tropical Cyclone Ita is bearing down on the Queensland Coast today. The storm is currently a category-5 tropical cyclone, according to Australia's Bureau of Meteorology. According to the 10PM (Australia Eastern Standard Time) advisory, Ita was packing wind gusts of approximately 285 km/hr (177MPH). These gusts would be well over category-5 intensity on the Saffir-Simpson Hurricane Wind Scale used in the United States, however, the Saffir-Simpson Scale categorizes according to sustained wind speed, so Ita would also be a major hurricane in the Western North Atlantic.


Satellite image of Tropical Cyclone Ita. Source: Australia Bureau of Meteorology


Ita will likely produce a large storm surge north of Cairns, with the highest levels likely north of Cape Flattery. Interestingly, the peak surge will likely be located just south of the location of Severe Tropical Cyclone Mahina's massive storm surge in 1899. Although scientific sources disagree about the details of Mahina's surge, many sources indicate that Mahina generated a 13.7-m (45 ft) storm tide near Bathurst Bay, Queensland. This water level ties Mahina with a Bangladesh surge in 1876 for the highest credible storm surge observation in the scientific literature. In short, Severe Tropical Cyclone Ita will likely produce a massive storm surge near the world's highest (tied for highest) historical storm surge site.

For the record, TC Mahina was more intense, with a lower central pressure than TC Ita. Mahina's central pressure was 915 hPa, which was the lowest on Australia's East Coast (Granger and Smith 1995), while TC Ita has a minimum central pressure of 934 hPa. Still, expect very strong winds and high surge with TC Ita.


Forecast track of Severe Tropical Cyclone Ita. The storm is forecast to strike the northern Queensland coast, north of Cooktown. Peak surge levels will likely occur north of Cape Flattery.


The Storm Surge Database (SURGEDAT) has now identified the location and height of peak storm surge for more than 700 global storm surges since 1880.  Australia and Oceania contain 134 observations in this dataset, including 69 observations from Queensland. TC Mahina (1899) is the largest surge observation in this region.

SURGEDAT contains a comprehensive dataset for Queensland from 1934-2011, with a limited amount of missing data. In that time frame, Queensland observed 31 surges > 1m, 14 surges > 2 m, 8 surges > 3m, and 3 surges > 5m. This means that per decade, Queensland averages 5.4 surges > 1 m, 2.5 surges > 2 m, 1.4 surges > 3 m, and 0.5 surges > 5 m. These statistics place Queensland, Australia as the fifth most active region in the world for tropical cyclone storm surges, according to the latest data from SURGEDAT.

The last surge in Queensland to exceed 5 m was the 5.33 m surge that was measured at the tide gauge in Cardwell, Australia, during Tropical Cyclone Yasi in 2011. Data Source: http://www.ehp.qld.gov.au/management/pdf/tc_yasi_feb_2011.pdf


TC Ita threatens to produce a large coastal flooding event north of Cairns, with highest water levels likely near and to the north of Cape Flattery. Stay tuned to the Australia Bureau of Meteorology and your favorite media outlets for updates on this dangerous storm.

Friday, November 22, 2013

"We were ready for the wind. We were not ready for the water."

Several articles have recently discussed the need for storm surge education, following Super Typhoon Haiyan's destructive storm surge in the Philippines. I've provided links to two articles below.

Lean Santos of Devex provides interesting insight into the challenges of communicating storm surge predictions to coastal populations in article #1 below.

Christopher Bodeen provides insights into the mindset of locals as this event unfolded, as well as some fascinating insights into evacuation options for people who live in a nation of many islands. See article #2 below.

He also provided a quote that may best summarize the need for education. He quotes senior presidential aide Rene Alemendras, who said, "I was talking to the people of Tacloban....They said 'we were ready for the wind. We were not ready for the water.'


Link #1:
https://www.devex.com/en/news/storm-surge-lost-in-translation-and-interpretation/82311?mkt_tok=3RkMMJWWfF9wsRonvaTAcu%2FhmjTEU5z16O8kUaSwhIkz2EFye%2BLIHETpodcMRcVkNq%2BTFAwTG5toziV8R7bNKc1r2NkQXBfn

Link #2:
http://www.startribune.com/politics/national/231415691.html


 Many people in the Philippines were not prepared for Haiyan's massive storm surge. The coastline of the Philippines contains many gulfs, bays and inlets, which create localized surge heights, making education efforts challenging in this region. Image: Associated Press


Many people have been asking me how it is possible that the people of the Philippines were not ready for this storm surge event, when they experience so many typhoons (hurricanes). Although such issues are complex, involving many physical and societal variables, we must remember a few things about this surge event and storm surge in the Philippines.

1. The magnitude of this catastrophe was truly extraordinary.

As explained on previous blog posts, it is thought that Haiyan produced stronger wind speeds at landfall than any tropical cyclone in world history. Also, the surge height appears to have exceeded 6 meters, which would place it close to the 7.3-meter storm surge of 1897 on Samar, Philippines. The 1897 event was the largest surge level in the modern history of East Asia.

2. Storm surge inundation in the Philippines tends to be very localized.

The coastal shape of the Philippines contains many gulfs, bays and inlets, as the Philippines are really comprised of numerous large and small islands. Storm surge tends to pile up in bays and inlets that are exposed to strong onshore winds. However, the area of the highest storm surge is often quite localized, and dependent upon the track of the storm.

Therefore, many typhoons may impact a given location over a period of several decades, but perhaps only one typhoon will generate a massive storm surge at that place, because the track needs to be just right to pile up surge along the coast. Such localized effects make storm surge education very difficult, because slight changes in storm tracks over the Philippines will often produce vast differences in coastal flooding patterns.


Hurricane Ike generated a widespread surge along the U.S. Gulf Coast in 2008. Much of Texas and South Louisiana would have been flooded even if Ike's track slightly shifted, because most of the coast is open and exposed to storm surge. In contrast, the coastal shape along the islands of the Philippines create very localized surge heights. Image: SCIPP/ SURGEDAT (Hal Needham).


In general, broader bodies of water with less islands tend to have less localized surge events, making education somewhat easier, because surges tend to be widespread. Take South Louisiana, for example. Most of the coastline is flat and exposed to the Gulf of Mexico. In 2008, Hurricane Ike made landfall in Texas, but generated a massive surge along the Louisiana Coast. However, if the track of Ike changed by 100 km (62 miles), most of South Louisiana would have still experienced a massive storm surge. In contrast, if Typhoon Haiyan's track had changed by 100 km, it is likely that the surge pattern would have been quite different, because the intricate shapes of the islands help generate different surge heights when the storm track changes.

The localized nature of surge in the Philippines may help explain why many people were taken off guard. Such people may be surprised to find out that future tropical cyclones with slightly different tracks may produce very different storm surge levels in hard-hit areas like Tacloban. Education efforts may help people to realize the causes of storm surge, as well as localized patterns in their region.

Friday, November 15, 2013

Super Typhoon Haiyan Storm Surge Animation


 Check out this storm surge animation for Super Typhoon Haiyan, provided by Deltares.

https://www.youtube.com/watch?v=8SH5fhGYCm0




Deltares link: www.deltares.nl/en

https://www.youtube.com/watch?v=8SH5fhGYCm0
 Deltares created a storm surge animation that shows computed surge levels for Super Typhoon Haiyan, which generated a devastating storm surge in the Philippines last week.


In personal correspondence with Jeff Masters of Weather Underground, Jeff told me that these surge levels were computed using Delft3D two days after landfall. The wind fields are based on JTWC data.

Thanks, Jeff, for passing this on, and great work by Deltares to model this event so quickly!

Haiyan Storm Surge Estimates Improve through Shared Observations


Estimates on Super Typhoon Haiyan’s massive storm surge height have improved through shared field observations and online collaboration.

Yesterday, I posted some photos sent to me by Aslak Grinsted, from the Niels Bohr Institute in Copenhagen, Denmark. Aslak had sent me photographs, which clearly showed the height of tree bark removal on trees in the surge impact zone.

How high was Super Typhoon Haiyan's destructive storm surge? Field observations and online collaboration are starting to provide some early estimates. Image: AP Photo/ Philippines Air Force

Just a few hours later, I received the following email from Vinny Burgoo, who was familiar with the area, knew the locations of the photos, and had some insight into the ground elevation.

Here is the e-mail:

Hi, Hal!

I've just read your blog about Aslak Grinsted's surge estimates for Typhoon Haiyan. Image #1 shows the southern end of the car park for Daniel Z. Romualdez Airport outside Tacloban City. Image #2 shows a queue at its northern end. See...


...(and the pix at Skyscraper City, below). Image #1's generators and the red collapsed slide or whatever it was are visible at the far end. Image #2's crumpled corrugated iron is visible in the foreground.

Image #3 is looking west across the northern end of the car park - and it *is* the same tree as in Image #2.

Elevation? The runway is said to be 3.0 m above MSL. An engineer's plan says a point just north of the terminal is '2.253' - presumably m above MSL. The plan is near the end of this page:


More pix of the post-typhoon airport are at the end of that thread.

Hope this helps a bit.

Regards,

Vinny Burgoo

Vinny mentioned that all three photographs were taken from the airport area. Image #1 on yesterday’s blog post was from the southern end of the carpark, while images 2 and 3 were taken from the northern end of the carpark.

The last link provides an architectural plan for proposed airport construction. Points on the map, accompanied by numbers, apparently show elevation levels. The map is oriented so right of the map is facing north.

This architectural map of the Tacloban Airport reveals elevation markers of 2.253 m (7.39 ft) very close to the location of the photographs sent in from Aslak Grinsted. Ground elevation values are essential for estimating surge heights when using high water marks or tree bark removal. Image: http://www.skyscrapercity.com/showthread.php?t=591415&page=78; Photo markups: Hal Needham

Three points on the map just south of the carpark are given an elevation of 2.253 m (7.39 ft), including the roundabout that is adjacent to the south end of the parking lot. This elevation seems like a reasonable estimate for the ground level in the photos, however, additional elevation information from multiple sources would be helpful for verification.

In image #2, Aslak estimated the surge height as 2 human heights, and in image #3, he estimated 2.5-3 human heights. According to Vinny, this is the same tree, located near the north end of the carpark. It goes without saying that it is difficult to make such estimates from photos taken at a distance, and Aslak did a great job by finding a few photographs with people in the picture to provide scale.

Locations of the photographs from Aslak Grinsted, posted on yesterday's blog. Vinny Burgoo identified the locations of all three photos, placing them at different ends of the airport carpark. Image: Google; Photo Markups: Hal Needham

If we assume the height of the tree bark removal reaches to 2.5 human heights, and we assume that the average adult human height in the photograph is approximately 1.7 m (5 feet 7 inches), then we receive an approximate elevation of 4.25 m (13.94 ft) for the height of tree bark removal above ground level.

However, the surge was higher than this level, because it took a certain amount of storm surge for the water to rise from Mean Sea Level (MSL) to ground level. Thus, we should add the ground elevation to our height. Adding 2.25 m (7.38 ft) to the water height gives us 6.5 m (21.33 ft), which we may use as a rough estimate of the surge height in this area.

Josh Morgerman submitted an Icyclone Chase Report to document the observations that he took alongside James Reynolds and Mark Thomas, from the Hotel Alejandro, in the heart of Tacloban City’s downtown district. The team was able to provide a storm surge observation, as the hotel they were staying in was inundated with water.

Quote from report:
“The storm surge rose very suddenly and rapidly, and it peaked near or after the center’s closest approach. The hotel flooded to a depth of ~4 ft. If the elevation at this location is truly 26 ft- as indicated by USGS- that suggests a storm surge of up to ~30 ft. It’s possible the elevation may have been as low as 15 ft, in which case, the surge was ~20 ft.”

The Icyclone Chase Team took storm observations from the Hotel Alejandro, in the heart of downtown Tacloban, about 15 nm north of the landfall location. Source: Icyclone Chase Report- Preliminary 

If the surge did indeed reach 30 feet (9.144 m) in downtown Tacloban, that water height would have been extraordinary, and would have smashed the previous surge record of 7.3 m (23.95 ft) for the Philippines and all of East Asia. The good news here is that we have a water height measurement from a fixed location, where the structure survived the storm. It will just take some time to verify the elevation of this hotel, in order to increase the confidence of this measurement. Google Earth provides an elevation of 7.32 m (24 feet) for the area near this hotel, which would provide a surge level of 28 feet (8.53 m). The Icyclone Chase Report does mention the possibility that the surge level could have been as low as 6.1 m (20 feet) in their location.

Early surge estimates are 6.5 m (21.33 ft) at the airport and 8.53-9.14 m (28-30 ft) in downtown Tacloban. Elevation estimates for the downtown observation is uncertain, the surge height in that location may be as low as 6.1 m (20 ft). Image: Google; Photo Markups: Hal Needham

Storm surge data often are provided from different sources with different measuring techniques. In this case, some observations are starting to come in, however, there is still quite a bit of uncertainty with these observations, and the values at this point are only rough estimates. It will be very helpful to verify the elevation of Hotel Alejandro, and any other high watermarks from buildings in the area that survived the storm. 


The surge estimate at the airport appears to have more accurate ground elevation information, however, the height of the tree bark removal depends on human height as a comparison. Meanwhile, the downtown observation has a more accurate read on the water level in the structure, however, the elevation at that location is more uncertain.

Commonly, when reconstructing a storm surge inundation, various observations have their strengths and weaknesses regarding accuracy of measurement. At this point, these surge estimates are very preliminary and are beginning to paint a picture of a surge that inundated this region with perhaps a 7.5 meter (24.6 foot) surge- give or take approximately several feet (one meter).

Estimates will improve as more information becomes available. Thanks so much to all who contributed by doing fieldwork, sending photos, or helping with photo interpretation. 


Thursday, November 14, 2013

Researcher Estimates Philippines Storm Surge Height from Denmark



After a major coastal flooding event, we want to know the maximum water height in various locations. Such information helps us better understand the process that triggered the event, and also helps us learn about localized flooding patterns.

Post-storm field surveys generally rely on trained field teams to go into an area and measure high-water marks. Such teams are generally looking for various clues that indicate the maximum water height. Signs on the landscape include the height of rafted debris, damage trimlines, tree bark removal, as well as mudlines or waterlines inside or outside standing structures.

Massive storm surges are so catastrophic that they destroy tide gauges as well as most buildings, making it difficult to obtain high water marks. After such disasters, measuring the height of tree bark removal is sometimes the best way to estimate surge heights. Photo: Noel Celis/ AFP/ Getty Images

A researcher from Denmark has already begun analyzing photographs for evidence of high-water marks, following Super Typhoon Haiyan’s massive storm surge in the Philippines. Aslak Grinsted, assistant professor at the Centre for Ice and Climate, at the Niels Bohr Institute, in Copenhangen, Denmark, has estimated the height of tree bark removal in numerous photographs from the impacted area. Such analysis is very valuable, because it provides some of the earliest estimates of surge height in the region.

Aslak Grinsted, assistant professor at the Centre for Ice and Climate, at the Niels Bohr Institute, has begun estimating  Haiyan's storm surge level by analyzing the height of tree bark removal in photos

Aslak sent me several photos earlier this week. Note the utter devastation in these photographs, as well as the fact that few structures remain standing to provide water lines or mudlines. In such massive surges, the height of tree bark removal often provides the best estimate of water levels, as debris floating on the top of the water column during the surge event rubbed off the tree bark.

Image #1 from Aslak Grinsted


Image #2 from Aslak Grinsted


Image #3 from Aslak Grinsted


Aslak compared the height of tree bark removal to the height of people in some of the photographs. In one photo, he estimated the height of tree bark removal to be approximately 2 human heights, while he estimated a water level of 2.5-3 human heights in another photo. If we assume the average human height in this area to be approximately 1.7 m (5 feet 7 inches), these approximations would provide estimates of surge levels reaching 3.4 m (11.2 ft) and 4.25-5.10 m (13.9-16.7 ft).

In order to accurately estimate the storm surge height, it is necessary to know the ground elevation for each observation, because storm surge is measured as the water height above the predicted tide level. Field teams will eventually provide accurate measurements, but in the meantime, online crowdsourcing may provide the best method for early surge estimates.

Here are some questions you could help with:



  •  In the photos that Aslak used to identify tree-bark removal, does anyone know the name of the location and/or the approximate ground elevation?

  •   Have you seen any photographs that contain clear signs of tree bark removal, rafted debris, mud lines, water lines, or damage trimlines on buildings/ structures?


If so, please send photos to Hal Needham at the following email: hal”at”srcc.lsu.edu. Please make sure to provide a citation and weblink for any photographs, if possible.

Aslak’s initial work this week has shown us the potential for all of us to participate in post-disaster field work, even from across the globe. As our world becomes more connected, opportunities should continue to open up for increased collaboration after such catastrophes.