The global tropical cyclone season of 2010: record inactivity
The year 2010 was one of the strangest on record globally for tropical cyclones. Each year, the globe has about 92 tropical cyclones--called hurricanes in the Atlantic and Eastern Pacific, typhoons in the Western Pacific, and tropical cyclones in the Southern Hemisphere. But in 2010, we had just 68 of these storms--the fewest since the dawn of the satellite era in 1970. The previous record slowest year was 1977, when 69 tropical cyclones occurred world-wide. Both the Western Pacific and Eastern Pacific had their quietest seasons on record in 2010, the Atlantic had its 3rd busiest season since record keeping began in 1851, and the Southern Hemisphere had a below average season. As a result, the Atlantic, which ordinarily accounts for just 13% of global cyclone activity, accounted for 28% in 2010--the greatest proportion since accurate tropical cyclone records began in the 1970s. Global Accumulated Cyclone Energy (ACE) for 2010 was the lowest since the late 1970s (ACE is a measure of the total destructive power of a hurricane season, based on the number of days strong winds are observed.)
Figure 1. Visible satellite image of 2010's strongest tropical cyclone: Super Typhoon Megi at 2:25 UTC October 18, 2010. A reconnaissance aircraft measured a central pressure of 885 mb and surface winds of 190 mph in the storm, making Megi the 8th strongest tropical cyclone in world history. Image credit: NASA.
A record quiet 2010 Northwest Pacific Typhoon Season
The Western Pacific set records for fewest number of named storms (fifteen, previous record seventeen in 1998) and typhoons (nine, tied with the previous record of nine in 1998. Note that Tropical Storm Mindulle was upgraded to a typhoon in post-analysis after the season was over.) Reliable records began in the mid-1960s. For just the second year in history, the Atlantic had more named storms and hurricane-strength storms than the Western Pacific. The only other year this occurred was in 2005. Ordinarily, the Western Pacific has double to triple the amount of tropical cyclones of the Atlantic. One other notable feature of the 2010 season was the lack of a land-falling typhoon on the Japanese mainland. This is only the second such occurrence since 1988.
In 2010, there was only one super typhoon--a storm with at least 150 mph winds--in the Western Pacific. However, this storm, Super Typhoon Megi, was a doozy. Megi's sustained winds cranked up to a fearsome 190 mph and its central pressure bottomed out at 885 mb on October 16, making it the 8th most intense tropical cyclone in world history. Fortunately, Megi weakened significantly before hitting the Philippines as a Category 3 typhoon. Megi killed 69 people on Taiwan and in the Philippines and did $700 million in damage, and was the second deadliest and damaging typhoon of 2010. Category 3 Typhoon Fanapi was the deadliest and most damaging typhoon of 2010, doing over $1 billion in damage to Taiwan and China and killing 105.
The record quiet typhoon season in 2010 was due, in part, to the La Niña phenomena. During such events, the formation region for Western Pacific typhoons moves northwestward, closer to China. Thus, storms that form in the Western Pacific spend less time over water before they encounter land, resulting in a lesser chance to become a named storm, and less time to intensify. They also accumulate a lower ACE due to their shorter duration. Since the Western Pacific is responsible for 35% of the world's major tropical cyclones, the global ACE value is strongly tied to year-to-year variations in the El Niño/La Niña cycle.
Figure 2. Statistics for the global tropical cyclone season of 2010. The two numbers in each box represent the actual number observed in 2010, followed by the averages from the period 1983-2007 (in parentheses). Averages and records were computed using the December 23, 2008 release of NOAA's International Best Track Archive for Climate Stewardship.
A record quiet 2010 Eastern Pacific Typhoon Season
In the Eastern Pacific, it was also a record-quiet season. On average, the Eastern Pacific has 15 named storms, 8 hurricanes, and 3 intense hurricanes in a season. In 2010, there were 8 named storms, 3 hurricanes, and 2 intense hurricanes. The previous record quietest season since 1966 was the year 1977, when the Eastern Pacific had 8 named storms, 4 hurricanes, and zero intense hurricanes. La Niña was largely responsible for the quiet Eastern Pacific hurricane season, due in part to the cool sea surface temperatures it brought. It is quite remarkable that both the Eastern and Western Pacific ocean basins had record quiet seasons in the same year--there is no historical precedent for such an occurrence.
Climate change and the 2008 global tropical cyclone season
We only have about 30 years of reliable global tropical cyclone data, and tropical cyclones are subject to large natural variations in numbers and intensities. Thus, it will be very difficult at present to prove that climate change is affecting global tropical cyclone activity. (This is less so in the Atlantic, where we have a longer reliable data record to work with.) A common theme of many recent publications on the future of tropical cyclones globally in a warming climate is that the total number of these storms will decrease, but the strongest storms will get stronger. For example, a 2010 review paper published in Nature Geosciences concluded: "greenhouse warming will cause the globally averaged intensity of tropical cyclones to shift towards stronger storms, with intensity increases of 2 - 11% by 2100. Existing modeling studies also consistently project decreases in the globally averaged frequency of tropical cyclones, by 6 - 34%. Balanced against this, higher resolution modeling studies typically project substantial increases in the frequency of the most intense cyclones, and increases of the order of 20% in the precipitation rate within 100 km of the storm centre." Last year, I discussed a paper by Bender et al that concluded that the total number of Atlantic hurricanes is expected to decrease by the end of the century, but there could be an increase of 81% in the number of Category 4 and 5 storms. The net effect of a decrease in total number of hurricanes but an increase in the strongest hurricanes should cause an increase in U.S. hurricane damages of about 30% by the end of the century, the authors computed, assuming that hurricane damages behave as they did during the past century. A new paper just published by Murakami et. al predicts that Western Pacific tropical cyclones may decrease in number by 23% by the end of the century, primarily due to a shift in the formation location and tracks of these storms.
In light of these theoretical results, it is interesting that 2010 saw the lowest number of global tropical cyclones on record, but an average number of very strong Category 4 and 5 storms. Fully 21% of last year's tropical cyclones reached Category 4 or 5 strength, versus just 14% during the period 1983 - 2007. Most notably, in 2010 we had the second strongest tropical cyclone on record in the Arabian Sea (Category 4 Cyclone Phet in June) and the strongest tropical cyclone ever to hit Myanmar/Burma (October's Tropical Cyclone Giri, an upper end Category 4 storm with 155 mph winds.) It is too early to read anything into this year's global tropical cyclone numbers, though--we need many more years of data before making any judgments on how global tropical cyclones might be responding to climate change.
Figure 3. Visible satellite image of Tropical Cyclone Phet on Thursday, June 3, 2010. Record heat over southern Asia in May helped heat up the Arabian Sea to 2°C above normal, and the exceptionally warm SSTs helped fuel Tropical Cyclone Phet into the second strongest tropical cyclone ever recorded in the Arabian Sea. Phet peaked at Category 4 strength with 145 mph winds. Only Category 5 Cyclone Gonu of 2007, which devastated Oman, was a stronger Arabian Sea cyclone. Phet killed 44 people and did $700 million in damage to Oman.
Figure 4. Visible MODIS satellite image of Tropical Cyclone Giri taken at 2:55am EDT October 22, 2010, just prior to landfall in Myanmar/Burma. At the time, Giri was a Category 4 storm with 145 mph winds. Giri killed 157 people and did $359 million in damage. Image credit: NASA.