Dale C. S. Destin |
By now you may have heard of Hurricane Alex, the first Atlantic hurricane to form in January since the only other one in 1938, according to HURDAT2. Alex is also only the third hurricane to exist over the Atlantic in January. There was Alice2 which formed late December 1954 and continued over into January 1955.
I suppose a few of the questions raised in some persons minds by Alex are: what does this mean for the upcoming hurricane season; does a January storm equate to an active or inactive season and was Alex caused by climate change?
Looking back at the three other times tropical cyclones – the generic name for depressions, tropical storms and hurricanes – formed in January for clues, I see none.
In 1978, there were 12 named storms (NS), 5 hurricanes and 2 major hurricanes (MH). In 1951, there were also 12 NS, with 8 becoming hurricanes and 3 MH. In 1938, the record shows that after Hurricane One in January, the eventual totals for the year were 9 NS, 4 hurricanes and 2 MH. Nothing unusual!
Based on El Nino Southern Oscillation data, which go back to 1950, Tropical Storm One of 1951 occurred during a moderate La Nina, whereas the 1978 system occurred during a weak El Nino. Of course, Alex formed in one of the strongest, if not the strongest El Nino on record.
Looking at the preceding hurricane seasons to the four January tropical cyclones, I also see nothing interesting.
In 1977, there were 6 NS, 5 hurricanes and a MH; 1950 had 16 NS, 11 hurricanes and 6 MH and 1937 had 11 NS, 4 hurricanes and a MH. And of course, in 2015, we had 11 NS, four hurricanes and 2 MH. Except for 1950, the other prior years had near normal number of storms.
Of the three previous years with January tropical cyclones, only one had a second preseason tropical cyclone formed before the official hurricane season – June 1 to Nov 30. This was 1951 with Hurricane Able in May. So, one cannot really say that January storms are a precursor to other preseason ones.
Looking a bit more broadly, there have been, at least, six years with preseason hurricanes (May 1970, May 1951, Jan 1938, March and May 1908, May 1889, May 1863) on record since 1851 prior to Alex. For such small sample sizes, no definite conclusions can be made. However, it may be instructive that these six seasons had near normal number of NS and hurricanes.
Here is what Dr. Rick Knabb – Director of the U.S. National Hurricane Center (NHC) – had to say on the meaning of Alex and preseason tropical cyclone activity:
— Dr. Rick Knabb (@NHCDirector) January 15, 2016
The activity of a hurricane season is more closely linked to the existing climate during the given season. This climate is very difficult to predict in advance of the season, which is evident by the fact that the best performing hurricane season forecasts are those issued around early August.
In speaking with Phil Klotzbach of Colorado State University via email, he shared the view that, “any tropical cyclone forming in January to be more responding to last year’s climate forcings than anything that would be present in 2016.”
So, Alex can be considered a super late hurricane that may be best credited to the 2015 hurricane season as opposed to being a super early system, which will be credited to the 2016 season.
Then there is the question of climate change, which has nothing to do with Alex. The previous three tropical cyclones forming in January occurred before 1979, pretty much predating climate change as an issue. This shows that January cyclones were more frequent before climate change was a concern.
Although HURDAT2 only has three tropical cyclones on record in January, it is a widely known fact that a number of such cyclones were missed prior to the satellite era and possibly shortly thereafter. This is especially so for those short-lived (lasting less than 48 hours) and forming in a similar area to that of Alex.
Given the advanced weather monitoring enterprise that exists today, we in the meteorological fraternity are pretty confident that no such system has formed in the past 20 years, at least. Thus, it would stand to reason that such January tropical cyclones like Alex are becoming fewer with climate change.
Further, according the IPCC, climate change is likely to cause a reduction in the number of tropical cyclones. Thus, based on our understanding of the science, it would be reasonable to expect that out-of-season tropical cyclones, such as Alex, will become even rarer as the more ideal conditions of the summer months would be required for their formation.
One of the things that climate change will alter, that will lead to fewer storms, is the lapse – the change of temperature with increasing height. It will cause it to decrease, leading to a less unstable, hurricane unfriendly atmosphere. In Alex’s case, the environmental lapse rate was very large contrary to the decreasing trend being caused by climate change.
Tropical cyclones in January and preseason hurricanes in general over the Atlantic are very rare; hence, the sample size is very small. Thus, one cannot be dogmatic about what Hurricane Alex means for the upcoming season. Notwithstanding, I am very confident that Alex is an aberration, virtually a freak hurricane, and means nothing for the upcoming hurricane season. It is also clearly not the fault of climate change, which is making it harder for hurricanes to form. Rather, it is simple natural climate variability.
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