Weather Extremes: Hurricanes and Tornadoes Likely to Diminish in 2021
/Despite the brouhaha over the recent record-breaking heat wave in the Pacific northwest and disastrous floods in Europe and China, windy weather extremes – hurricanes and tornadoes – are attracting little media attention because they’re both on track for a relatively quiet season.
Scientists at the Climate Prediction Center of NOAA (the U.S. National Oceanic and Atmospheric Administration) don’t anticipate that 2021 will see the record-breaking 30 named storms of 2020, even though they think the total may still be above average. However, of last year’s 30 storms, only 13 became actual hurricanes, including 6 major hurricanes. The record annual highs are 15 hurricanes recorded in 2005 and 8 major hurricanes in 1950.
Hurricanes are classified by their sustained wind speeds on the Saffir-Simpson scale, ranging from Category 1, the weakest, to Category 5, the strongest. A major hurricane is defined as one in Category 3, 4 or 5, corresponding to a top wind speed of 178 km per hour (111 mph) or greater. NOAA predicts just 6 to 10 hurricanes this year, with 3 to 5 of those being in the major hurricane categories.
Hurricanes in the Atlantic basin, which has the best quality data available in the world, do show heightened activity over the last 20 years, particularly in 2005 and 2020. This can be seen in the figure below, depicting the frequency of all Atlantic hurricanes from 1851 to 2020. But researchers have found that the apparent increase in recent times is not related to global warming.
Rather, say the scientists who work at NOAA and several universities, the increase reflects natural variability. Although enhanced evaporation from warming oceans provides more fuel for hurricanes, recent numbers have been artificially boosted by a big improvement in our ability to detect hurricanes, especially since the advent of satellite coverage in the late 1960s. And global warming can’t be the explanation, as the earth was cooling during the previous period of increased activity in the 1950s and 1960s.
Prior to that time, most data on hurricane frequency were based on eyewitness accounts, thus excluding all the hurricanes that never made landfall. What the researchers did was examine the eyewitness records, preserved by NOAA workers, in order to calculate the ratio of Atlantic hurricanes that didn’t come ashore to those that did, both in the modern era and in the past. The observations of non-landfalling hurricanes before the early 1970s came primarily from ships at sea.
Then, using a model for the radius of hurricane or major hurricane winds, the researchers were able to estimate the number of hurricanes or major hurricanes going back to 1860 that were never recorded. Their analysis revealed that the recent hike in the hurricane count is nothing remarkable, being comparable to earlier surges in the early 1880s and late 1940s. In the U.S., the past decade was in fact the second quietest for landfalling hurricanes and landfalling major hurricanes since the 1850s. Hurricane Ida was the first major U.S. landfalling hurricane this year.
Tornadoes, which occur predominantly in the U.S., have been less violent and fewer in number than average so far in 2021. Like hurricanes, tornadoes are categorized according to wind speed, using the Fujita Scale going from EF0 to EF5; EF5 tornadoes attain wind speeds up to 480 km per hour (300 mph).
Up to the end of August, 958 tornadoes had been reported by NOAA’s Storm Prediction Center in 2021 – of which 740 had been confirmed, according to Wikipedia. These numbers can be compared with the January to August average of 1035 confirmed tornadoes; the yearly average is 1253.
The annual incidence of all tornadoes in the U.S. shows no meaningful trend from 1950 to 2020, a period that included both warming and cooling spells, with net global warming of approximately 1.1 degrees Celsius (2.0 degrees Fahrenheit) during that time. But the number of strong tornadoes (EF3 or greater) has declined dramatically over the last half century, as seen in the next figure illustrating the number observed each year from 1954 to 2017.
Clearly, the trend is downward instead of upward. Indeed, the average number of strong tornadoes annually from 1986 to 2017 was 40% less than from 1954 to 1985. In May this year, there wasn’t a single strong tornado for the first time since record-keeping began in 1950. Although there’s debate over whether the current system for rating tornadoes is flawed, 2021 looks like being another quiet year.
Next: What “The Science” Really Says about the Coronavirus Pandemic
