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.

1 comment:

  1. Great post. I saw these two models :

    It will be interesting to compare these to the data as it comes in...