Tag Archives: tropical cyclone

Covering All Bases: Modeling Typhoon and Non-Typhoon Driven Flood in the Philippines

In a country that is used to the regular rhythm of typhoon seasons, 2017 disrupted the pattern and was a surprisingly quiet year in terms of landfalling typhoons in the Philippines. While 26 named storms formed in the western North Pacific basin, equaling the long-term average, all other tropical cyclone statistics fell below the 1981-2010 average. Only 12 of these named storms developed into typhoons, and just four reached a strength of category 3 or above on the Saffir-Simpson scale. No typhoons made landfall in the Philippines during the year for only the fifth time in recorded history.

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Asia’s Costliest Cyclones: The Curse of September

The northwest Pacific is the most active tropical cyclone basin in the world, having produced some of the most intense and costly cyclone events on record. The 2015 typhoon season has been particularly active due to this year’s strong El Niño conditions.

The unpredictable nature of the El Niño phenomenon, which affects the genesis and pathway of tropical cyclones, and the complexity of tropical cyclone systems underscore the need to fully understand typhoon risk—particularly in Japan where exposure concentrations are high. Catastrophe models, such as the forthcoming RMS® Japan Typhoon Model, using a basin-wide event set to model the three key correlated perils—wind, inland and coastal flood—are more effective in enabling firms to price and manage the ever-evolving exposures that are at risk from this multifaceted peril.

The Significance of September

Peak typhoon season in the northwest Pacific basin is between July and October, but it’s September that typically sees the highest number of strong category 3-5 typhoons making landfall: eight of the top ten greatest insured losses from northwest Pacific tropical cyclones since 1980 all occurred in September.

In September, during El Niño years, Guam is significantly more susceptible to a higher proportion of landfalls, and Japan and Taiwan experience a slight increase due to the genesis and pathway of tropical cyclones. While wind is the primary driver of tropical cyclone loss in Japan, inland and coastal flooding also contribute substantially to the loss.

In September 1999, Typhoon Bart caused $3.5 billion in insured losses due to strong winds, heavy rainfall, and one of the highest storm surges on record at the time. The height of the storm surge reached 3.5 meters in Yatushiro Bay, western Japan, and destroyed coastal defences, inundating vast areas of land.

Five years later in September 2004, Typhoon Songda caused insured losses of $4.7 billion. Much of the loss was caused by rain-related events and flooding of more than 10,000 homes across South Korea and Japan in the Chugoku region, western Honshu.

Table 1 Top 10 Costliest Tropical Storms in Asia (1980-2014):

Date Event Affected Area Maximum Strength (SSHWS) Insured Loss ($mn)
Sept, 1991 Mireille Japan Cat 4 6,000
Sept, 2004 Songda Japan, South Korea Cat 4 4,700
Sept, 1999 Bart Japan, South Korea Cat 5 3,500
Sept, 1998 Vicki Japan, Philippines Cat 2 1,600
Oct, 2004 Tokage Japan Cat 4 1,300
Sept 2011 Roke Japan Cat 4 1,200
Aug – Sept, 2004 Chaba Japan, Russia Cat 5 1,200
Sept, 2006 Shanshan Japan, South Korea Cat 4 1,200
Sept, 2000 Saomai Japan, South Korea, Guam, Russia Cat 5 1,100
Sept, 1993 Yancy Japan Cat 4 980

Munich Re

September 2015 – A Costly Landfall for Japan?

This September we have already seen Tropical Storm Etau, which brought heavy rains to Aichi Prefecture on Honshu Island causing immense flooding to more than 16,000 buildings, and triggered dozens of landslides and mudslides.

The increased tropical cyclone activity in the northwest Pacific this year has been attributed to an El Niño event that is forecast to strengthen further. Two factors linked to El Niño events suggest that this September could still see a costly landfall in Japan:

  • El Nino conditions drive the formation of tropical cyclones further eastward, increasing the travel times and distances of typhoons over water, giving rise to more intense events.
  • More northward recurving of storms produces tropical cyclones that track towards Japan, increasing the number of typhoons that could make landfall.

Combined, the above conditions increase the number of strong typhoons that make landfall in Japan.

Damaging Typhoons Don’t Just Occur In September

Damaging typhoons don’t just occur in September or El Niño years – they can happen under any conditions.

Of the ten costliest events, only Typhoon Mireille in 1999 and Typhoons Songda, Chaba, and Tokage, all of which made landfall in 2004, occurred during El Niño years

Look out for more information on this topic in the RMS paper “Effects of the El Niño Southern Oscillation on Typhoon Landfalls in the Northwest Pacific”, due to be published in October.

Reflecting on Tropical Storm Bill

After impacting coastal Texas and portions of the Plains and Midwest with rain, wind, and flooding for nearly a week, Tropical Storm Bill has dissipated, leaving the industry plenty to think about.

The storm organized quickly in the Gulf of Mexico and intensified to tropical storm status before making landfall in southeast Texas on June 16, bringing torrential rain, flash flooding, and riverine flooding to the region, including areas still trying to recover from record rainfall in May. Many surrounding towns and cities experienced heavy rain over the next few days, including some that recorded as much as 12 inches (30 cm). Thankfully though, most high exposure areas like Houston, TX, were spared of significant flooding.

Source: NOAA

Still, as damage is assessed and losses are totaled, Tropical Storm Bill reminds us of the material hazard associated with tropical cyclone (TC)-induced precipitation, and the importance of capturing its impacts in order to obtain a comprehensive view of the flood risk landscape. Without understanding all sources of flood hazard or their corresponding spatial and temporal correlation, one may severely underestimate or inadequately price a structure’s true exposure to flooding.

Of the $40 billion+ USD in total National Flood Insurance Program claims paid since 1978, more than 85% has been driven by tropical-cyclone induced flooding, approximately a third of which has come from TC-induced rainfall.

The most significant TC-rain event during this time was Tropical Storm Allison (2001), which pummeled southeast Texas with extremely heavy rain for nearly two weeks in June 2001. Parts of the region, including the Houston metropolitan area, experienced more than 30 inches (76 cm) of rain, resulting in extensive flooding to residential and commercial properties, as well as overtopped flood control systems. All in all, Allison caused insured losses of $2.5 billion (2001 USD), making it the costliest tropical storm in U.S. history.

Other notable TC-rain events include Hurricane Dora (1964), Tropical Storm Alberto (1994), Hurricane Irene (2011). In the case of Irene, the severity of inland flooding was exacerbated by saturated antecedent conditions. Similar conditions and impacts occurred in southeast Texas and parts of Oklahoma ahead of Tropical Storm Bill (2015).

Looking ahead, what does the occurrence of two early-season storms mean in terms of hurricane activity for the rest of the season? In short: not much, yet. Tropical Storms Ana and Bill each formed in areas that are most commonly associated with early-season tropical cyclone formation. In addition, the latest forecasts are still predicting a moderate El Nino to persist and strengthen throughout the rest of the year, which would likely suppress overall hurricane activity, particularly in the Main Development Region. However, with more than five months remaining in the season, we have plenty of time to wait and see.

Christmas Day Cyclone – Lessons Learned 40 Years After Tracy

December 25, 2014 marks 40 years since Cyclone Tracy made landfall early Christmas Day over the coast of Australia, devastating the Northern Territory city of Darwin. As the landfall anniversary approaches, we remember one of the most destructive storms to impact Australia and are reminded of the time when “Santa Never Made it into Darwin.”

Image credit: Bill Bradley

Small and intense, Tracy’s recorded winds reached 217 km/hr (134 mph), a strong category 3 on the 5-point Australian Bureau of Meteorology scale, before the anemometer at Darwin city airport failed at 3:10 am, a full 50 minutes before the storm’s eye passed overhead. Satellite and damage observations suggest that Tracy’s gust winds may have topped 250 km/hr (155 mph) and the storm’s strength is generally described as a category 4. At the time, it was the smallest tropical cyclone ever recorded in either hemisphere, with gale force winds at 125 km/hr (77 mph) extending just 50 km (31 mi) from the center and an eye only about 12 km (7.5 mi) wide when it passed over Darwin. (Tracy remained the smallest tropical cyclone until 2008 when Tropical Storm Marco recorded gale force winds that extended out to only 19km (12 mi) over the northwestern Caribbean).

Although small, Cyclone Tracy passed directly over Darwin and did so while tracking very slowly—causing immense devastation, primarily wind damage and predominantly residential structural damage. Around 60 percent of the residential property was destroyed and more than 30 percent was severely damaged. Only 6 percent of Darwin’s residential property survived with anything less than minor damage. Darwin had expanded rapidly since the 1950s, but throughout that time structural engineering design codes were typically not applied to residential structures.

The insurance payout for Tracy was, at the time, the largest in Australian history at 200 million (1974) Australian dollars (AUD), normalized to 4 billion (2011) AUD, according to the Insurance Council of Australia. It has been surpassed only by the payout from the 1999 Sydney Hailstorm at 4.3 billion (2011) AUD.

The RMS retrospective report that was released around the 30th anniversary of the storm provides information on the meteorology of the cyclone and the wind damage. The report also highlights the impact on wind engineering building codes (particularly residential) that were introduced as a result of the cyclone during reconstruction in Darwin and in cyclone affected regions of Australia—resulting in some of the most stringent building codes in cyclone-exposed areas across the world.

Darwin was completely rebuilt to very high standards and relatively new, structurally sound buildings now dominate the landscape. Most certainly, Darwin is better prepared for when the next cyclone strikes. However, the building stock in other cyclone-exposed cities of Australia is mixed. Most coastal cities are a blend of old, weak buildings and newer, stronger buildings, which are expected to perform far better under cyclone wind loading. The benefits of improvements in both design code specifications and design code enforcement have been demonstrated in Queensland by Cyclones Larry (2006) and Yasi (2011). Most of the damage to residential buildings in those storms was suffered by houses constructed before 1980, while those built to modern codes, incorporating the lessons learned from Cyclone Tracy, suffered far less damage. While progress has clearly been made, it is sobering to remember there are many more pre-1980 houses remaining in cyclone-prone areas of Australia.

Australia Cyclone season runs from November to April. The 2014/2015 season is forecast to be an average to below average season in terms of tropical cyclone activity off Australia waters, according to the Australian Government Bureau of Meteorology .

Michael Drayton contributed to this post. Michael Drayton has been developing catastrophe models for RMS since 1996. While based in London, he worked on the first RMS European winter storm model and U.K. storm surge models, lead the development of the first RMS basin-wide Atlantic hurricane track model, and oversaw the hazard development work on the first RMS U.K. river flood model. Since moving back to New Zealand in 2004, Michael has updated the RMS Australia cyclone hazard model and led the development of the RMS Australia (Sydney) severe convective storm model. He works on U.K. storm surge updates and supports U.S. hurricane model activities including audits by the Florida Commission on Hurricane Loss Projection Methodology. Ever since the 2011 Christchurch earthquake, Michael has been increasingly involved with the local insurance market and research communities. He received a BS degree in civil engineering, with honors, from the University of Canterbury and a PhD in applied mathematics from King’s College, Cambridge.