Thunderstorms 101

Learn how thunderstorms form, what causes lightning and thunder, and how these violent phenomena help balance the planet’s energy and electricity.


Major environmental disasters: August 2017

Hurricane Harvey is likely to be one of the costliest natural disasters on record for the economy of the United States, with damage from the hurricane to minimally cost tens of billions of dollars, Aon Benfield has reported.

Impact Forecasting, Aon Benfield’s catastrophe model development team, released on Friday its monthly Global Catastrophe Recap report, which evaluates the impact of the natural disaster events that occurred worldwide during August.

Harvey came ashore in Texas on Aug. 25 to become the first major hurricane (a storm rated as either Category 3, 4 or 5) to make landfall in the U.S. since Hurricane Wilma in 2005. Heavy rain continued until Aug. 31, bringing record-breaking rainfall to some areas. Catastrophic flooding ensued across a swath of eastern Texas and southwestern Louisiana, as more than 60 people were confirmed dead and dozens more were injured. Additional impacts due to severe thunderstorms and flash floods were noted across the Gulf states (including Alabama, Florida and Mississippi) and Mississippi Valley.

Total economic losses were estimated to minimally reach the tens of billions (in U.S. dollars), “ensuring that Harvey is likely to become one of the costliest natural disasters on record in the U.S.,” the release said. “Preliminary published reports suggest that insured losses – including those paid by private industry and the U.S. National Flood Insurance Program – were likely to well exceed US$10 billion.”

In Canada, the report referenced a slow-moving storm system that prompted heavy rainfall across part of Ontario from Aug. 28 to 29, causing widespread flooding. The worst damage was noted in parts of Windsor, Tecumseh and Essex. Total economic and insured losses were expected to reach into the millions in U.S. dollars.

Elsewhere, Typhoon Hato and Tropical Storm Pakhar both made landfall in China’s Guangdong province within one week of each other, causing considerable damage and loss of life in multiple provinces as well as Macau and Hong Kong. Economic losses from Hato alone were minimally estimated at US$3 billion, while combined insured losses from both storms were estimated at US$535 million.

Other nat cats that occurred worldwide in August include:

  1. More than 1,300 people killed across South Asia due to extensive monsoonal flooding and landslides during August. Throughout India, Bangladesh, and Nepal, tens of millions of people were affected, as approximately one million homes were damaged or destroyed.
  2. Multiple rounds of flooding impacted several Chinese provinces claiming at least 100 lives and generating aggregated economic losses in excess of US$1.2 billion;
  3. Floods in northern Vietnam claimed 40 lives and caused losses of US$88 million;
  4. Torrential rainfall over portions of Africa during August led to at least two significant landslides that claimed an estimated 1,250 lives. The largest of these occurred in Sierra Leone on Aug. 14, where the death toll in Freetown was estimated at approximately 1,050;
  5. Several rounds of severe weather including at least two derechos (windstorms) impacted multiple central European countries through the middle part of August. Widespread property, agricultural and forestry damage was reported from Poland, the Czech Republic, Slovakia, Germany, Switzerland and Austria. Economic and insured losses expected to reach well into the hundreds of millions in euros; and
  6. On Aug. 8, a magnitude-6.5 earthquake struck China’s Sichuan province, damaging 72,500 homes.

PDF Icon View the full Impact Forecasting August 2017 Global Catastrophe Recap report (PDF)

Source: Canadian Underwriter

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Major environmental disasters: July 2017

Relentless seasonal flooding that began in mid-June resulted in continued fatalities and damage across parts of Asia in July, causing an estimated US$11 billion in economic losses, according to Impact Forecasting’s latest Global Catastrophe Recap report.

Impact Forecasting noted that the greatest flooding impacts in Asia were recorded in China, where the Ministry of Civil Affairs listed combined economic flood damage at more than US$10 billion during a six-week stretch, much of which occurred in the Yangtze River Basin. Nearly 200 people were left dead or missing and hundreds of thousands of homes were damaged or destroyed.

Heavy flooding also occurred in Japan following the landfall of Tropical Storm Nanmadol and “abundant remnant moisture associated with a frontal boundary,” with more than 2,600 homes and other structures damaged or destroyed as extensive flooding and landslides affected Fukuoka, Oita, Shimane, Kumamoto and Hiroshima prefectures, the statement said. Total economic losses were expected to near US$1 billion.

Pictures Of The Week Photo Gallery
People swim past the top of a pagoda at a flooded riverside park in Wuhan in central China’s Hubei Province.

In Canada, intense heat and gusty winds led to hundreds of wildfires and “numerous reports of damage” in British Columbia, where a state of emergency was declared. Officials reported that 240 wildfires were at one point active in July. The British Columbia government announced that it had allocated CAD100 million (USD78 million) to help areas rebuild.

In Alberta, up to tennis ball-sized hail fell on July 23, accompanied by strong winds and heavy rain, the report noted. Hail caused extensive damage to vehicles, houses, crops and other property, while high winds downed multiple trees and power poles, tore shingles off roofs and toppled grain bins. Impact Forecasting estimated the economic loss at US$50+ million.

Other natural hazard events throughout July included:

  • Officials in Italy reported that prolonged drought conditions have cost the economy about US$2.3 billion in economic losses. Production of vegetables, fruits, cereals, vines, and olives were all impacted by the abnormally dry conditions which prevailed across the country during the first half of 2017;
  • Monsoon rains killed hundreds and caused major damage to structures, agriculture and infrastructure in parts of India, Bangladesh and Pakistan. Total economic damage in the hundreds of millions in U.S. dollars;
  • Seasonal rains in Thailand killed at least 23 people and caused economic damage in excess of US$300 million, while flash flooding in northern Switzerland prompted claims payouts of nearly US$90 million;
  • Two separate instances of powerful thunderstorms resulted in considerable damage in Turkey, marked by large hail and flooding throughout the greater Istanbul metro region. Turkish insurers anticipated combined claims payouts reaching US$440 million;
  • Additional severe thunderstorms and subsequent flooding affected many sections of the U.S.. Damage and casualties resulting from large hail, straight-line winds, isolated tornadoes were noted in the Midwest, Plains, Southeast, Mid-Atlantic and the Desert Southwest. Total combined economic and insured losses were expected to enter the hundreds of millions in U.S. dollars;
  • Tropical Storm Talas made landfall in Vietnam, causing US$44 million in economic damage;
  • Strong earthquakes were recorded in the Philippines, Greece, Turkey and China.

PDF Icon View the full Impact Forecasting July 2017 Global Catastrophe Recap report (PDF)

Source: Canadian Underwriter

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Major environmental disasters: June 2017

Impact Forecasting has published the latest edition of its monthly Global Catastrophe Recap report, which evaluates the impact of the natural disaster events that occurred worldwide during June 2017.

A thunderstorm over Saskatoon on June 2 that spawned ping pong ball-sized hail is estimated to cost more than US$30 million, Aon Benfield said in its Global Catastrophe Recap report for the month of June.

South of the border, the worldwide economic and insured losses during June were once again largely driven by several major severe weather outbreaks in the United States. Large hail, tornado touchdowns, straight-line winds and isolated flash flooding all contributed to an aggregated economic loss that was expected to exceed US$3 billion. Of that total, public and private insurance entities were expected to minimally cover at least US$2 billion.

On June 7, a powerful low pressure system left 11 people dead in South Africa as it lashed the country’s southwestern coast, the report said. Widespread damage and disruption was reported throughout the Western Cape region as the storm produced powerful wind gusts and lightning strikes that triggered numerous fires. The deadliest and costliest fire burned near Knysna as thousands of homes, structures and vehicles were damaged or destroyed. Published reports indicated that insurance payouts from the wildfires and storms could cost the local industry as much as US%305 million. Overall economic losses were estimated at more than US$500 million, the report said.

Greek firefighters stand on the ruins of a collapsed house in the village of Vrissas, on the island of Lesbos in the eastern Aegean.

In China, major flooding impacted at least nine provinces in the southern part of the country during June, killing at least 31 people and affecting more than 130,000 homes. The catastrophe was caused by torrential downpours associated with annual Mei-yu rains, Aon explained. China’s official Ministry of Civil Affairs listed aggregated economic losses at more than US$2.4 billion, which resulted in the flooding becoming the costliest individual global natural catastrophe in the month of June.

Other natural peril events during June included:

  • Thunderstorm activity in Europe peaked on June 22, when a particularly violent outbreak caused significant losses to German insurers, estimated at US$455 million;
  • Torrential monsoonal rainfall caused floods and landslides in Bangladesh and neighbouring northeast India, causing at least 169 fatalities;
  • Other flood-related events in Asia (including China, Taiwan, Indonesia, Bangladesh, and India) resulted in a combined death toll of at least 312 people;
  • Additional significant floods occurred in Central America, Chile and Western Africa;
  • The combination of extreme heat and dry thunderstorms led to one of the deadliest wildfires in Portuguese history, killing 64 people and destroying hundreds of homes and businesses. Local government indicated that economic losses may reach US$565 million; and
  • An offshore magnitude-6.3 earthquake damaged more than 1,100 homes on the Greek island of Lesbos. Economic losses were expected to be tens of millions (in U.S. dollars).

View the full Impact Forecasting June 2017 Global Catastrophe Recap report (PDF)

Source: Canadian Underwriter

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Did you know that the hurricane naming system originates from World War II?

On Aug. 23, 2005, a troubling tropical depression began to form just off the coast of the southeastern Bahama Islands. Six days later, after first making landfall in southern Florida as a Category 3 storm, Hurricane Katrina would hit southeastern Louisiana with winds up to 140 mph, leaving in its wake a path of destruction and damage that would render almost half of a million people homeless.

Its name became so infamous that the World Meteorological Organization (WMO) chose to remove it permanently from their list of potential hurricane names the following year.

But what exactly constitutes a retired storm name? And how do hurricanes even get their name in the first place?

Dan Kottlowski, a senior AccuWeather meteorologist offered an explanation as to how the system works and where it came from:

“During World War II, it became highly noticed that [the United States] was losing ships in the west Pacific because of hurricanes. So, coming out of the war, a large amount of research took place to understand these storms and make people more aware of them. As a part of that project, [the military] started naming them.”

Did you know that the hurricane naming system originates from World War II?

Kottlowski went on to explain that initially, these names were based on the military’s phonetic alphabet. However, beginning in 1979, the WMO started using a repeating system of human names in an effort to standardize the practice.

The system works differently depending on where the storm in question occurs. Hurricanes occurring in the Atlantic basin are named based upon six, alphabetized, 21-name lists (Q, U, X, Y and Z are all skipped). The lists cycle on a six-year rotation, so every seventh year, the process reverts back to the first list.

In the event that more than 21 storms occur within a single hurricane season, which happened most recently in 2005, the Greek alphabet is utilized to name the remaining storms.

The Eastern Pacific basin uses the same cycling list system; however, its lists consist of 24 names (only Q and U are skipped). Different names are also utilized for each letter to better represent the traditions of that particular region.

Atlantic Names
Atlantic Names
Eastern North Pacific Names
Eastern North Pacific Names

The outlier is the Central North Pacific basin. Hurricanes in this region are named based on four, 12-name lists and, rather than cycle through the lists year by year like the other two basins, the Central North Pacific goes through the names one by one, starting a new list only when the bottom of the previous is reached.

In order to earn a name, systems must exhibit sustained winds of 39 mph, the lower limit for tropical storm categorization. Once sustained winds pass 73 mph, the storm is then officially referred to as a hurricane.

Storms below the 39 mph threshold are simply referred to as tropical depressions, which are not given names.

When it comes to retiring storm names, Kottlowski explained that the process, although subjective, is generally fairly consistent.

“Almost every large, devastating storm that has ever affected the United States has been retired,” he said. “Those names are [subsequently] replaced by other names.”

The decision to retire a storm’s name is made at the WMO’s yearly conference.

A complete list of hurricane names by basin can be found here.

Source: AccuWeather

Risk of Gulf of Mexico tropical system increases

Waters around southeastern Mexico and over the south-central Atlantic have the potential to yield the next tropical systems of the 2017 hurricane season.

Tropical system may form near the southwestern Gulf of Mexico next week

A broad area of disorganized showers and thunderstorms over Central America will drift northward over the Yucatan Peninsula of Mexico this weekend.

“This feature has a good chance to become a tropical depression and tropical storm next week,” according to AccuWeather Hurricane Expert Dan Kottlowski. “There are still multiple scenarios for development and track at this time.”

Risk of Gulf of Mexico tropical system increases; Another threat may follow in central Atlantic

A clockwise flow of dry air is forecast to develop over the southeastern United States early next week. If this scenario unfolds and lingers, then Florida and the northeastern Gulf of Mexico could be sheltered from the storm.

However, if this feature is weak or breaks down, then the door could be opened for the tropical system to drift into the northeastern Gulf of Mexico.

While winds aloft over the Yucatan Peninsula, the southwestern Gulf of Mexico and the northwestern Caribbean Sea are currently too strong to allow development to occur, these disruptive winds are projected to ease next week. A situation to be closely monitored.

Tropical wave over the central Atlantic bears watching

A second area of concern in the Atlantic basin is a strong tropical wave that recently moved off the west coast of Africa.

Tropical waves are clusters of showers and thunderstorms that move westward near the equator. Over time, these clusters can begin to spin and evolve into a tropical depression, tropical storm and hurricane.

Tropical development in this part of the Atlantic during June is rare.

The next names on the list of tropical storms for the 2017 are Bret and Cindy. Tropical Storm Arlene formed and dissipated in the middle of the Atlantic during April. Arlene never directly affected any land areas.

Source: AccuWeather