Winter brings about the most active period of weather here in the northeast, but it’s also a good time to look back at the most recent season of hurricanes and tornadoes.
Hurricane season ended November 30th and while the eastern Pacific was very active, the Atlantic season was again relatively quiet.
Tornadoes are most frequent in the spring and early summer with a smaller peak in the fall. The end of December isn’t usually very active for tornadoes since most of the country is typically in cool conditions and daylight is at a seasonal minimum.
A Quiet Season
Hurricanes are nature’s way of moving the excess heat that builds up in the tropics to points north. They need the right atmospheric conditions to form and if there are missing pieces , the season ends up quieter than average. According to Gerry Bell, Ph.D., the lead forecaster at the Climate Prediction Center, “A combination of atmospheric conditions acted to suppress the Atlantic hurricane season, including very strong vertical wind shear, combined with increased atmospheric stability, stronger sinking motion and drier air across the tropical Atlantic. “Also, the West African monsoon was near- to below average, making it more difficult for African easterly waves to develop.”
We tend to focus on hurricanes in the Atlantic because Pacific hurricanes don’t hit the big cities of the west coast. Moisture from Pacific storms can help with drought conditions as was the case when rains associate with hurricanes Odile and Simon pushed into parts of the southwestern U.S which has been exceedingly dry for several years.
One storm which received a lot of press was r Hurricane Iselle which reached major hurricane status, (category 3 or higher) and impacted the Big Island of Hawaii in early August, but only as a tropical storm This was the first tropical storm to hit the big island since 1992.
The ACE index measures the wind energy of a tropical cyclone and is calculated by NOAA every six hours. According to Dr. Ryan Maue’s chart below from WeatherBell Analytics, this year’s overall ACE is running 92% of average for the entire globe. You can see the ACE of the individual regions as well.
No Major Hits
In spite of all the hoopla every time a tropical system develops we continue to enjoy the longest period on record with a major hurricane hitting the United States mainland. While some of this is certainly just plain old luck, the last major hurricane to strike the US was hurricane Wilma, which made landfall on Oct. 24, 2005.
Tornadoes Also Fewer
The chart below through December 10th tells the story of this year’s tornado season.
The back line represents the number of tornadoes reported this year as compared to other years. If you look at just the raw numbers it seems like this year is not only going to be one of the lowest ever, but perhaps even THE lowest ever. However, records from past decades are likely too low because of the lack of reporting and there is some double counting might inflate other numbers.
Even without 100% accurate data, the trend is clear, 2014 is now the third year of lower than average tornadoes in the United States. Looking back to 1953, this year, 2014, stands out as a very low year for these types of storms.
The chart below shows the 30 year average of how many tornadoes hit each state.
You might wonder if the low incidence of tornadoes and hurricanes is related. While the atmospheric conditions are different needed for each of these types of storms to form, there may in fact be some underlying connection among all of the various oscillations and teleconnections that exist, even if meteorologists and climatologist aren’t yet aware of them.