Monday, July 7, 2014

Super Typhoon Bart (1999) May Provide Insight on Neoguri Surge Potential



Super Typhoon Neoguri is a powerful typhoon packing winds of 130 kts (150 mph). The cyclone is forecast to strengthen to a category-5 typhoon, with winds reaching 140 kts (161 mph) as it tracks towards Japan. Image:NOAA


Super Typhoon Neoguri is now a well-developed tropical cyclone, packing winds of 130 knots (150 mph). The Joint Typhoon Warning Center forecasts strengthening of this typhoon, as maximum sustained winds may reach 140 knots (161 mph), while it tracks west of Okinawa. Such intensification would make Neoguri a category-5 hurricane if it were located in the Atlantic Ocean.

This typhoon is forecast to track W of Okinawa, before curving towards the NE and making landfall on the Japanese Island of Kyushu. Although Neoguri is forecast to weaken to a category-3 typhoon by landfall, storm surge correlates better with pre-landfall winds than wind speeds at landfall (Jordan and Clayson 2008; Needham and Keim 2014), so a relatively large storm surge may still occur.



Super Typhoon Neoguri is forecast to pass W of Okinawa as a category-5 tropical cyclone, then curve towards the NE, before making landfall as a major tropical cyclone on the island of Kyushu, Japan. Source:Weather Underground



Neoguri may take a similar track towards Kyushu as Super Typhoon Bart in 1999. Bart also passed west of Okinawa as a category-5 typhoon, before moving NE and making landfall on Kyushu with maximum sustained winds of 115 mph. Maximum sustained wind speeds of Bart and Neoguri may be comparable as they track west of Okinawa and move towards landfall in Kyushu.

Bart generated a 3.5 m (11.5 ft) storm surge in Yatushiro Bay (Kawai et al. 2009), which tied it for first place with Typhoon Vera in 1959 as the highest storm surge in Japan’s history, according to SCIPP's global SURGEDAT dataset. SURGEDAT has identified the location and height of 11 historical storm surge events in Japan since 1911. Unfortunately, Bart’s surge peaked near the time of a spring high tide, which further exacerbated storm surge flooding. This enabled flood waters to reach the roofs of one-story houses, while the surge claimed 12 lives (Kawai et al. 2009).

Super Typhoon Bart (1999) followed a similar track and had similar intensity as the forecast track and intensity of Super Typhoon Neoguri. Bart passed west of Okinawa as a category-5 typhoon, and then weakened to a category-3 typhoon with winds of 100 kts (115 mph) at landfall on Kyushu, Japan. Map Source: Unisys Corporation.


However, when Bart made landfall on Kyushu, it passed just west of Yatushiro Bay, enabling the storm to push a tremendous amount of water into the bay on strong southerly winds. We still do not know if Neoguri will take a similar track. If Neoguri tracks farther east, for example, it would pass to the east of Yatushiro Bay, enabling the strongest winds to blow offshore out of the bay. Therefore, while Bart's surge history may provide some general insights about surge potential from Neoguri, slight differences in typhoon track may result in large differences in surge heights at specific locations.




Super Typhoon Bart tracked just west of Yatushiro Bay, Japan, enabling strong south winds to push a 3.5 m (11.5 ft) storm surge into the Bay. This surge level is tied for Japan's highest water level in SCIPP's SURGEDAT database. Slight differences between Bart's and Neoguri's tracks may drastically change surge heights at specific locations. Image and info: Hal Needham



STORM SURGE OFTEN VERY LOCALIZED ON ISLAND NATIONS

On island nations like Japan and the Philippines, a slight change in a typhoon track can change surge levels at a particular location dramatically. Deep inlets and bays, as well as jagged island coastlines oriented in different directions makes surge levels very localized in these countries. This was made obvious last autumn, when powerful Super Typhoon Haiyan generated a catastrophic, but localized storm surge in the Philippines. Bays and inlets near the location of landfall greatly enhanced surge levels around places like Tacloban, which observed a wall of water more typical of a tsunami than a storm surge.

Neoguri will be monitored very closely and slight changes in track forecast will likely result in large changes in storm surge heights. Coastal populations should be aware that storm surge in such situations is very localized, as one location may observe a high storm surge, but another location 20 km away may observe little or no storm surge. The most vulnerable areas to surge will be locations that are exposed to strong, onshore winds.

References:
Jordan II, M.R., and C.A. Clayson, 2008: Evaluating the usefulness of a new set of hurricane classification indices. Monthly Weather Review, 136, 5234-5238.
Kawai, H., N. Hashimoto, and M. Yamashiro, 2009: Real-time Probabilistic Prediction of Storm Water Level at Japanese Ports. Proceedings of the Nineteenth (2009) International Offshore and Polar Engineering Conference, Osaka, Japan, June 21-26, 2009. International Society of Offshore and Polar Engineers (ISOPE).

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.


Thursday, July 3, 2014

Hurricane Arthur Bears Down on North Carolina

Hurricane Arthur was bearing down on North Carolina this evening as a category-1 hurricane with maximum sustained winds of 90 mph, according to the National Hurricane Center. They predict that Arthur may intensify to a category-2 hurricane at landfall or it's closest approach to the coast.

Hurricane Arthur's eye is clearly visible just southeast of Wilmington, North Carolina, on this radar image provided by Weather Underground's WunderMap. The National Hurricane Center said Arthur's eyewall was just east of Cape Fear.

The National Hurricane Center forecasts that storm surge could inundate land areas, reaching the following heights if the timing of peak surge occurs at high tide:

3-5 feet above ground level in the coastal areas of North Carolina within the hurricane warning;
2-4 feet above ground level in Pamlico and Albemarle Sounds;
1-3 feet above ground level in Southern North Carolina and Northeastern South Carolina;
1-3 feet above ground level in Extreme Southeastern Virginia.

Keep in mind, those are not storm surge heights above mean sea level, but actually above ground level. 

Extensive storm surge history is available for North Carolina, as this region is familiar with visits from hurricanes and tropical storms. The Program for the Study of Developed Shorelines at Western Carolina University has developed an extensive dataset, as well as an interesting fact sheet about historic storm surges in North Carolina. This page is called, Cataloging all Available Storm Surge Measurements for the State of North Carolina: The National Storm Surge Database, and is available on the Web at: https://shoreline.wcu.edu/Katie/SS_SEGSA_2011.pdf.

 The Program for the Study of Developed Shorelines at Western Carolina University has developed extensive storm surge data and mapping capabilities, as well as useful information about past surges in North Carolina

This website shows the capabilities of their database combined with GIS mapping, which enables them to consider how storm surge is affected by various hurricane parameters, like hurricane track and angle of a hurricane's approach to a coastline. In regards to North Carolina storm surges, they provide a top 10 list of high water marks available in their dataset, including the following observations, which were the highest in North Carolina for each of these hurricanes:

Storm Name    Year    High Water Mark (ft)      Location
Hazel               1954              18                       Brunswick
Isabel              2003              16.2                     Dare
Fran                1996              15.4                     New Hanover
Ione                1955              15.1                     Craven

Western Carolina University's National Storm Surge Database project has developed various technological tools, including a Storm Surge Viewer and other products that enable users to view storm surge observations and hurricane tracks.

The Southern Climate Impact Planning Program (SCIPP) has also developed extensive storm surge data for North Carolina. So far, SCIPP has identified 989 storm surge observations in the state. These data are provided for 46 separate tropical cyclones since 1857.

SCIPP has also developed mapping work that provides historical storm surge/ storm tide heights, as well as the tracks of historic hurricanes that produced such high water marks. For example, the image below is a SCIPP map of Hurricane Hazel's track and high water marks in 1954. This map is not intended to be a comparison to Arthur's storm surge in any way, but rather a snapshot of the capabilities of this database and mapping work.

 SCIPP map of Hurricane Hazel's track and storm surge/ storm tide observations in 1954. According to the Program for the Study of Developed Shorelines at Western Carolina University, Hazel's 18-ft storm surge was the highest in the history of North Carolina.



Tuesday, June 3, 2014

Female-Named Hurricanes Have Produced Slightly Higher Storm Surges than Male Hurricanes

The media world is buzzing about an article recently published in the Proceedings of the National Academy of Sciences. Kiju Jung, of the University of Illinois at Urbana-Champaign, and colleagues, published an article titled, "Female hurricanes are deadlier than male hurricanes." The article claims that female-named hurricanes are more deadly because the public perceives such storms to be less threatening than male-named hurricanes.

The Economist wrote about this article yesterday (http://www.economist.com/news/science-and-technology/21603243-it-sounds-incredible-hurricanes-womens-names-kill-more-people-do) and many people have been posting articles supporting or criticizing the findings of the article by Jung et al.

Eric Holthaus critiqued these findings in an online post this morning: http://www.slate.com/blogs/future_tense/2014/06/03/are_hurricanes_named_after_women_more_dangerous_not_so_fast.html.

 Hurricane Sandy's massive storm surge along the Mid-Atlantic Coast proved deadly in 2012. A recent article suggests that female-named hurricanes may be more deadly than male-named hurricanes because people see them as less of a threat. Image: NOAA.

I was curious to look at differences in storm surge levels of female- and male-named storms over time to see if storm surge was possibly a contributing factor to higher death tolls in female-named storms. Although the study started analyzing data with the year 1950, I only used the data from 1979- present, because this later time period contained both female and male-named storms. During the 34-year period of 1979-2012, the study by Jung et al. analyzed data for 27 male and 27 female storms. 


I found that during this period female-named hurricanes produced slightly higher storm surges than male hurricanes. The female-named storms produced an average surge level of 9.94 ft (3.03 m), whereas the male storms produced an average surge level of 9.58 ft (2.92 m). This means that female storms have produced surges about 3.8% higher than male storms.

The study by Jung et al. removed Hurricanes Katrina and Audrey as outliers. Audrey occurred in 1957, so it is outside the 34-year window of comparison, however Hurricane Katrina occurred in 2005 and would be included in my surge analysis if it were in the original study. Katrina would change things quite a bit, as it's 28-ft (8.53-m) storm tide was the largest modern-day coastal flooding water mark in the Western Hemisphere. If Katrina were included, then female-named storms would then produce an average surge height of  10.6 ft (3.23 m), which is about 11.1% higher than male storms.

 Not including Katrina, the highest three storm surges from male and female-named hurricanes since 1979 were:

MALE                                                          FEMALE

Name        Year        Water Level (ft)           Name           Year          Water Level (ft)
Hugo         1989        20.2 (storm tide)         Rita              2005         17.8 (storm tide)
Ike             2008       17.5 (storm tide)         Sandy           2012         17.5 (storm tide)
Andrew     1992        17.1 (storm tide)         Isabel           2003         16.2 (storm surge)


These data came from SURGEDAT, a global storm surge database we've constructed through the NOAA-funded Southern Climate Impacts Planning Program (SCIPP). Where possible, I used storm surge heights, but in some cases storm surge obs were not available, so I used storm tide heights. Although I've noted storm tide datums as much as possible, I have not yet adjusted all of these heights to a common datum, so datum differences do cause slight errors in these values.

Whether you agree or disagree with the findings by Jung et al., it is hurricane season, so we can expect the media to be picking up on more hurricane-related news. Stay tuned to Hurricane Hal's Storm Surge blog for storm surge context/ climatology related to active hurricanes and tropical cyclones this season.

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.