Hurricane Dorian: Just Weather, Not Climate Change
We made it three weeks without extreme weather and/or climate change hysteria making rounds on social media. Unfortunately, that streak has come to an end, making the lives of most weather forecasters like me a lot more difficult.
We are at the climatological peak of the Atlantic hurricane season¹ (September 10th) (Figure 1), thus it should be NO surprise to anyone that we have seen an uptick in tropical activity. However, I stand corrected － people are losing their minds about it.
Hurricane Dorian is now a Category 1 storm (as of the time I wrote this article – September 6 at 9:06 PM EST) with maximum sustained winds at 92 miles per hour (80 knots), and it’s quickly pulling offshore moving northeast (Figure 2).²
Dorian ravaged the Bahamas over Labor Day Weekend, as it stalled over Grand Bahama Island as a Category 5 hurricane. According to official reports, at least 30 people have died and unfortunately, that death toll is expected to rise in the coming days.
According to Dr. Philip Klotzbach, a meteorologist at Colorado State University, Dorian was the most intense hurricane (by wind speed and minimum central pressure) to strike the Abaco Islands and Grand Bahama.³
It was also the first Category 5 hurricane to make landfall on either island within the period of record keeping, which dates back to 1851.³ Hurricane Dorian also tied with the Labor Day (1935), Gilbert (1988), and Wilma (2005) for the second strongest hurricane on record in the Atlantic basin by wind speed (185 mph or 160.8 knots).³
The only hurricane that was stronger by wind speed was Hurricane Allen in 1980, which had maximum sustained winds as high as 190 miles per hour (165.1 knots).³
As usual, government officials, journalists, and even some meteorologists have taken these statistics and have been promoting climate alarmism about how hurricanes are becoming increasingly intense due to man-made climate change.
They argue that warming oceans are providing more fuel to hurricanes, which is indeed true, however, that’s only one part of the story.
Without looking at hurricane mechanisms, it’s easy for one to be susceptible to these ideas. Therefore, it’s important we take a step back and look at the big picture.
Debunking the SST myth
I want to debunk the popular myth that has been circulating around the internet. Warmer sea surface temperatures (SST) does not guarantee that hurricanes will become more frequent or more intense.
While warm water temperatures extending from the surface down to around 150 feet (45.72 meters) below the ocean surface are required to be warmer than 80°F (26.67°C) for “fuel” for a tropical cyclone to develop,⁴ there are many other factors that govern hurricane activity not only on short-term time scales, but also decadal and millennial time scales, the latter of which I’m not going to explore in this article.
Warmer sea surface temperatures do not spontaneously spawn hurricanes. It just doesn’t work that way. Most of the time, there has to be a pre-existing atmospheric disturbance, preferably an area of low pressure where thunderstorms can form around (as that’s essentially what a hurricane is).
Low atmospheric pressure is caused by the convergence (meeting) of winds in the low levels of the atmosphere. Where these winds meet, they are forced to rise.
In the Northern Hemisphere, low pressure systems spin counterclockwise as a result of the Coriolis Force. The Coriolis Force in and of itself initiates vorticity in the atmosphere whereby winds can converge at the surface.
In addition to low-level convergence, the atmosphere in the lower to mid-levels of the troposphere must be fairly saturated in order for tropical cyclogenesis.⁴
The air becomes more humid if there is more evaporation occurring, which is a function of warm sea surface temperatures.⁴
Once the atmosphere in the low and mid-levels of the atmosphere is saturated, that means clouds will form as the air reaches the dew point temperature whereby water vapor must condensate out into liquid water droplets.⁴
If there is very high thermodynamic instability, or a sharp decrease in temperature with altitude, then more condensation will occur. The more condensation that occurs releases latent heat into the atmosphere, causing it to warm up (Figure 3).⁴
As the warmer air rises and expands, it’s forced to diverge once it reaches the tropopause and flow clockwise, thereby decreasing the air pressure at the surface.⁴
If the outflow of winds high in the troposphere is outpacing the converging winds at the surface, the air pressure will decrease around the center of the storm.⁴ If the central air pressure in the eye decreases, the storm will strengthen.⁴
The lower the minimum central pressure of a tropical cyclone is, the sharper the pressure gradient (change in air pressure with distance) will be between the eye and the surrounding environment. This sharp gradient creates an imbalance which the atmosphere tries to equalize by increasing the wind speed.
While warm sea surface temperatures, high moisture content, vorticity, and low pressure are needed for hurricane development, other factors like dry air and wind shear can drastically weaken a tropical cyclone or inhibit any tropical development altogether.⁴
If dry air is too abundant, that suppresses convection (cloud building), and if wind shear is too high, then the hurricane becomes vertically tilted or disorganized, cutting off the updrafts formed by convergence.⁴
Whether natural or man-made, global warming periods are known to increase the frequency of El Niño events because of the general warmth.⁵ ⁶ When there is an El Niño occuring, wind shear in the Atlantic tends to dominate preventing tropical cyclones from developing.⁵
La Niña years conversely tend to produce more hurricanes in the Atlantic basin due to lesser wind shear. It is for this reason for why I think that the Atlantic basin was very quiet between 2005 and 2017. Keep in mind, hyperactive seasons like 2005, 2017, and even 2018 (not hyperactive, but bad) were La Niña years.⁷
Thus, one has a really hard time making the argument that global warming will produce stronger and more frequent hurricanes in the Atlantic. There’s no sound science or statistics to back claims like that.
There are other theories that suggest that while hurricanes will NOT become more frequent or intense due to climate change, they may become more wetter. By wetter, they mean increased rainfall. This is an interesting and plausible theory. NOAA has suggested it.
But, until we start to see increases in hurricane rainfall, this theory doesn’t hold water.
REFERENCES
[1] “Tropical Cyclone Climatology.” National Hurricane Center. Accessed September 6, 2019. https://www.nhc.noaa.gov/climo/.
[2] Cowan, Levi. “Current Storm Information.” Tropical Tidbits. September 6, 2019. Accessed September 6, 2019. https://tropicaltidbits.com/storminfo/.
[3] Klotzbach, Philip. “Hurricane Dorian Meteorological Records/Notable Facts Recap.” Colorado State University. September 5, 2019. Accessed September 6, 2019. https://tropical.colostate.edu/media/sites/111/2019/09/Hurricane_Dorian_Records.pdf.
[4] “Hurricanes: growth processes.” WW2010. 2010. Accessed September 6, 2019. http://ww2010.atmos.uiuc.edu/(Gh)/guides/mtr/hurr/grow/home.rxml.
[5] “Hurricanes: Interaction with El Niño.” WW2010. 2010. Accessed September 6, 2019. http://ww2010.atmos.uiuc.edu/(Gh)/guides/mtr/hurr/enso.rxml.
[6] Gale, Kaitie. “The multivariate ENSO Index.” ResearchGate. September 2018. Accessed September 6, 2019. https://www.researchgate.net/figure/1-The-multivariate-ENSO-Index-Data-source-NOAA-ESRL-Physical-Sciences_fig3_327559287.
[7] “El Niño and La Niña Years and Intensities.” Golden Gate Weather Services. July 2019. Accessed September 6, 2019. https://ggweather.com/enso/oni.htm.
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Andy Rowlands
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Hi Chris, with the likes of the IPCC continuing to claim storms will increase in number and intensity with a warming climate, a couple weeks ago I emailed Dr Tim Ball to ask him:-
“I don’t know whether this is your field as such, but as I understand it, storms are produced because of the temperature difference between the poles and the tropics, and if the world warms, that temperature difference is reduced as the poles warm faster than the tropics, so less storms are produced, and those that do form are less intense, apart from the odd rogue one.
If that’s right, then if the world cools, as appears to be happening as we enter the solar minimum, that temperature difference increases as the poles cool quicker than the tropics, so more storms are produced, and they are more intense.”
He replied the same day:- “Your comment is correct as it applies to most storms. They occur along the boundary between the cold air dome over the of the polar regions and the warm tropical air of the atmosphere. This is generally known as the Polar Front and occupies the middle latitudes between 30° and 65°. The only storms that form differently begin close to the equator as a line of thunderstorms known as an Easterly Wave. They remain in a line until they move outside of 8° of the equator. This is because Coriolis Force is too weak in that latitude zone each side of the equator to form the spinning motion necessary for a storm to intensify. Once Coriolis Force is adequate the line of thunderstorms forms a circle with an area of high pressure at the centre, this area of clear skies at the centre of a hurricane is known as the eye.
As you correctly note, the intensity of the storm is determined by the temperature difference across that Polar Front. Also, as you correctly note the IPCC claim storms will increase in numbers and intensity with global warming. In fact, there is more warming in the polar region. This will reduce the temperature difference and thus the number and intensity of storms.”
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jerry krause
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Hi Andy
You wrote: “I emailed Dr Tim Ball to ask him:- “I don’t know whether this is your field as such, but as I understand it, storms are produced because of the temperature difference between the poles and the tropics,””
And you wrote that he replied: ““Your comment is correct as it applies to most storms. They occur along the boundary between the cold air dome over the of the polar regions and the warm tropical air of the atmosphere.””
I suggest that you both read my comment I just made at Judith Curry’s article (https://principia-scientific.com/climatologist-climate-change-and-hurricanes-link-over-hyped/) and Chapter 6 (Vertical Convection: cumuliform clouds, showere, and thunderstorms) of R.C. Sutcliffe’s 1966 book–Weather and Climate.
Have a good day, Jerry
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