Despite what may be said in the press the number of tropical storms / hurricanes during the years 2000 to 2017 has been fairly constant. The average number of named storms in that 17 year period is 43, with 2016 and 2017 both having exactly the average number of storms.
The data used for these numbers can be seen here (has link to original data)
It can be seen from the chart above that there appears to be very little difference between now (end 2017 ignoring 2018) and the year 2000 with an up period down period and up period in between. Looking at the trend over this period we can see in the chart below that the linear trend is flat and the 4th order polynomial trend shows the wave in the pattern.
In fact the linear trend is exactly the average which would indicate that overall there is no change in the number of storms per year.
Now some will say “Ah but the intensity of the storms has increased massively”. Has it? Let’s examine that premise.
If we look at a storm such as ITA in 2014 we can see that the storm duration was reported as from 04 April to 14 April. Up to 0600 Zulu (GMT/UTC) on 08 April the storm was a Tropical storm. During the 8th it was Cyclone 1 so for the 8th it is counted as one unit of force. Shown below as *
On the 9th it was one, rising to Cyclone 2 by the evening so it is counted as 2 ** for the day. On the 10th it was 4 **** and on the 11th it was Cyclone 4 dropping to Cyclone 1 so the whole day is counted as Cyclone 4 ****. It was back to a tropical storm again on the 12th.
The comparison gives one a better idea than using just the duration since ITA was 11 days duration, but was only Category 4 on 2 of those days, Cat 2 on 1 day, Cat 1 on 1 day. 11 units of force where as if you take the whole period at the promulgated category 4, because that is how these are reported, that would be 11 days at 4 units of force = 44 units.
Date: 04-14 APR 2014 Cyclone-4 ITA ADV LAT LON TIME WIND PR STAT 1 -11.30 156.10 04/04/18Z 35 - TROPICAL STORM 2 -11.80 155.70 04/05/06Z 45 - TROPICAL STORM 3 -12.20 154.90 04/05/18Z 45 - TROPICAL STORM 4 -12.10 153.90 04/06/06Z 45 - TROPICAL STORM 5 -12.30 153.50 04/06/18Z 45 - TROPICAL STORM 6 -12.10 153.50 04/07/06Z 45 - TROPICAL STORM 7 -11.70 153.20 04/07/18Z 60 - TROPICAL STORM 8 -11.50 152.50 04/08/06Z 65 - CYCLONE-1 * 9 -11.40 152.00 04/08/18Z 70 - CYCLONE-1 * 10 -11.50 150.20 04/09/06Z 80 - CYCLONE-1 ** 11 -11.70 148.70 04/09/18Z 90 - CYCLONE-2 ** 12 -12.50 147.10 04/10/06Z 115 - CYCLONE-4 **** 13 -13.30 146.00 04/10/18Z 135 - CYCLONE-4 **** 14 -14.50 145.40 04/11/06Z 125 - CYCLONE-4 **** 15 -15.50 145.00 04/11/18Z 75 - CYCLONE-1 **** 16 -16.70 145.30 04/12/06Z 50 - TROPICAL STORM 17 -17.80 146.00 04/12/18Z 45 - TROPICAL STORM 18 -20.10 148.30 04/13/06Z 45 - TROPICAL STORM 19 -22.20 151.70 04/13/18Z 45 - TROPICAL STORM 20 -23.70 155.10 04/14/06Z 40 - TROPICAL STORM
By using the number of units of force on any given day we can get a much better idea of the intensity of the storms. We have seen that the number of storms is steady so what about the intensity as we are led to believe this is increasing.
Actually the trend is dead level on the linear and possibly even declining ever so slightly on the polynomial 4th order trend.
If we look at what is being reported against what actually happened we see what appears to be a slight increase in the number of days being reported causing an increase in the scariness of the storm. 2015 appears to be a weird anomaly as the reported number of days way exceeds to actual number – in excess of one third above the ‘normal’ ratio. In reality 2015 was no worse than 2003, 2004 or 2012
The data for this is:
So is that apparent slight change in the number of days and thus units a change? Yes it is! The tend in the difference ratio is UP whereas the trend in the number of days and/or storm intensities is not.
The XLSX file for the above data may be downloaded here