America’s “hurricane guru,” the late Dr. Bill Gray, emeritus professor of atmospheric science at Colorado State University, showed that the seasonal hurricane frequency is determined by six factors:
* The rotational tendency, or vorticity, already present in the atmosphere
* Pressure gradients determined by latitude
* Wind shear, the changes in wind speed and direction that occur between layers in the atmosphere. High wind shear can tear storms apart before they form tropical cyclones. Low wind shear allows storms to grow into hurricanes if the other conditions are right.
* Ocean thermal energy
* The rate of change of temperature with altitude
* Relative humidity in the mid-troposphere
This year the sea surface temperature of the Atlantic Ocean has indeed been relatively high (contributing to Dr. Gray’s factors #4 and #6 above) since we are in a warm phase of the natural Atlantic Multidecadal Oscillation (AMO). But the AMO’s origin and the mechanisms directing it are as yet unknown.
Joe D’Aleo, co-chief meteorologist at
Weatherbell.com said, “Not every meteorologist believes 2020 holds the record for most named storms. Due to advances in technology, forecasters are able to identify smaller subtropical storms that may have gone unnoticed in the past. Some of this year’s storms should not have been named or would not have been in previous years.”
Christopher Landsea, chief of the tropical analysis and forecast branch at the National Hurricane Center, was cited in the New York Times as saying, “There has been a lot of hype about the record number of storms and, yes, it’s been a busy year. There have been horrific impacts. But is this really a record? The answer is no.”
D’Aleo points out that this conclusion is supported by the trend in annual North Atlantic Accumulated Cyclone Energy (ACE, a metric used to express the energy of tropical cyclones during a period of time). The following graph shows that 2020 was 13th in ACE levels since 1851.
Commenting on the fact that the ACE trend in the Pacific is only 50% of normal in 2020, D’Aleo said, “For the northern hemisphere [it] was 80% of normal. So even with the hyper Atlantic season. GLOBALLY we were BELOW average.”
Next D’Aleo showed the following graph of landfalling (on the continental U.S.) hurricanes, and concluded that “the decadal trend for landfalling hurricanes and major hurricanes has been down.”
The global warming/hurricane connection completely falls apart when one looks more closely at the observational data.