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:

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:

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:

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: 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: 

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:

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.