Florida Main Hurricane Strikes: No Vital Improve in Depth from Sea Floor Warming
Reposted from Dr. Roy Spencer’s Weblog
September 4th, 2019 by Roy W. Spencer, Ph. D.
Abstract: Twenty-two main hurricanes have struck the east coast of Florida (together with the Keys) since 1871. It’s proven that the noticed enhance in depth of those storms at landfall resulting from SST warming over time has been a statistically insignificant zero.43 knots per decade (zero.5 mph per decade). Thus, there was no noticed enhance in landfalling east coast Florida main hurricane power with warming.
Within the information reporting of main Hurricane Dorian which devastated the NW Bahamas, it’s generally assumed that hurricanes on this area have turn into stronger resulting from warming sea floor temperatures (SSTs), which in flip are assumed to be attributable to human-caused greenhouse gasoline emissions.
Right here I’ll use observational information for the reason that 1870s to deal with the query: Have landfalling main hurricanes on the east coast of Florida elevated in depth from warming sea floor temperatures?
The rationale I’m solely addressing landfalling hurricanes on the east coast of Florida is three-fold: (1) this space is a hotbed of main hurricane exercise; (2) the document is for much longer for landfalling hurricanes, since earlier than the early 1970s the depth of main hurricanes properly offshore was rather more unsure; and (three) the coastal inhabitants there may be now a number of million individuals, the area south of West Palm Seashore is traditionally liable to main hurricane strikes, and so the query of whether or not hurricane depth there has elevated resulting from ocean warming is of nice sensible significance to many individuals.
First let’s begin with the document of main hurricane strikes on the east coast of Florida, together with the keys. There have been 22 such storms since 1871, occurring fairly irregularly over time.
Whereas there was a slight enhance within the depth of those storms over time, amounting to +zero.eight knots per decade, the correlation is sort of low (zero.21) and the quantitative relationship is simply barely vital on the 1-sigma degree.
However this doesn’t inform us the function of sea floor temperatures (SSTs). So, subsequent let’s look at how SSTs have modified over the identical time frame. Since all of those main hurricanes made landfall within the southern half of Florida, I selected the next boxed area (22N-28N, 75W-82W) to compute area-averaged SST anomalies for all months from 1870 by way of 2018 (HadSST information obtainable right here).
Since 18 of the 22 main hurricane strikes occurred in both August (four) or September (14), (and four had been in October), I targeted on the common SST anomaly for the 2-month durations August-September. Right here’s the 2-month common SST anomalies for 1870-2018.
Be aware that the years with main hurricane strikes are marked in pink. What stunned me is that the SST warming on this area throughout peak hurricane season (August/September) has been very weak: +zero.02 C/decade since 1871, and +zero.03 C/decade since 1950.
If we then examine SST anomaly with storm depth at landfall, we get the next plot. Right here I took into consideration which month the hurricane occurred in for the needs of computing a 2-month SST anomaly. For instance, if the storm hit in October, I used the September/October common. If landfall was in August, I used the July/August common.
There’s a weak relationship between SST and storm depth (correlation = zero.19), however the regression coefficient (+13.5 kts/deg. C warming) isn’t statistically vital on the 1-sigma degree.
Now, if we simply ignore statistical lack of significance and assume these quantitative relationships are principally sign fairly than noise, we will multiply the zero.03 C/decade SST warming development since 1950 by the 13.5 kts/deg C “warming sensitivity parameter”, and get +zero.43 kts/decade of storm depth enhance per decade resulting from SST warming, which is sort of precisely zero.5 mph per decade.
That is an exceedingly small quantity. That might be 5 mph per century.
So, primarily based upon the noticed SST information from the Hadley Centre, and hurricane information from the Nationwide Hurricane Heart, we conclude that warming SSTs have induced a tiny enhance in depth of landfalling main hurricanes by zero.5 mph per decade.
I believe a statistician (which I’m not) would say that that is within the noise degree.
In different phrases, there is no such thing as a observational proof that warming SSTs have made landfalling hurricanes on the east coast of Florida any stronger.
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