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9:45 AM | *A down year for tornadoes in the US and likely the first with none classified as “violent”...an above-normal Atlantic Basin tropical season*

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Weather forecasting and analysis, space and historic events, climate information

9:45 AM | *A down year for tornadoes in the US and likely the first with none classified as “violent”...an above-normal Atlantic Basin tropical season*

Paul Dorian

The preliminary number of tornadoes in the US through December 26th is 988 which puts 2018 way down in the lowest 25th percentile compared to climatological records. Source: NOAA

The preliminary number of tornadoes in the US through December 26th is 988 which puts 2018 way down in the lowest 25th percentile compared to climatological records. Source: NOAA

Overview 
As the year winds down, it appears this will be another down year for tornadoes in the US and likely the first one in recorded history without any classified as “violent”.  The preliminary tornado count in the US for the year places 2018 in the lowest 25th percentile and this will likely become the first year since modern records began in 1950 with no tornadoes ranked as EF4 or EF5 (i.e., “violent”).  The great news here is that the number of tornado-related deaths in the US during 2018 is near record low levels.  As far as hurricanes are concerned, the Atlantic Basin tropical season was above-normal for the year, but about half as intense as 2017.  Unfortunately, the 2018 Atlantic tropical season will be remembered for two deadly and damaging hurricanes – Florence which generated tremendous flooding over the Carolinas and Michael which made landfall in the Florida Panhandle as one of the strongest ever in that part of the country.

EF3/EF4 “violent” tornadoes have trended down in the US since 1950. Source: NOAA, Washington Post

EF3/EF4 “violent” tornadoes have trended down in the US since 1950. Source: NOAA, Washington Post

Tornadoes

The trend for tornadoes in recent years across the US has been for below-normal activity and 2018 is shaping up as being easily down in the lowest 25th percentile based on climatology.  In addition, the 2018 season is likely to be the first in recorded history (since 1950) with zero EF4 or EF5 “violent” tornadoes. Furthermore, the year will not only likely set a record for zero “violent” tornadoes – those ranked EF4 or EF5 on a 5-point scale – but will likely also set the record for the fewest “intense” tornadoes (i.e., EF3). According to the Washington Post, 2018 has seen only 12 “intense” tornadoes in the US, three fewer than the record low year of 1987 which had 15. The great news here is that the number of tornado-related deaths of 10 in the US is near a yearly historic low.  The last year that came close to reaching this milestone was 2005 when the first “violent” tornado did not actually occur until November 15th – much later than is normal for being the first of the year which typically happens in the early spring. This year’s pattern seems to fit a recent trend. There have been down-trends in “violent” tornado numbers both across the entire modern period, and when looking at just the period since Doppler radar was fully implemented across the country in the mid-1990s.

The preliminary number of tornadoes in the US for 2018 puts us well below the average of the base period 2005-2015. Source: NOAA

The preliminary number of tornadoes in the US for 2018 puts us well below the average of the base period 2005-2015. Source: NOAA

One possible cause for the lack of violent tornadoes this year is the fact that cold high pressure tended to be more dominant than normal throughout the spring peak tornado season. This was particularly so during April and May, when tornado numbers were below to well below normal, and cold air often dominated the scene across the Midwest and Plains. Although the country ended up seeing a number of memorable tornado events after the spring, including several this fall, in most years over half of the tornadoes occur from March through May. Making up those numbers is difficult at other times of the year when ingredients for them are less likely.

A preliminary summary of the 2018 Atlantic Basin tropical season. Source: Philip Klotzbach (Colorado Sate University), NOAA

A preliminary summary of the 2018 Atlantic Basin tropical season. Source: Philip Klotzbach (Colorado Sate University), NOAA

Hurricane season

This year’s Atlantic Basin tropical season featured only slightly above the normal number of storms, but two were deadly and did billions of dollars’ worth of damage to the US mainland. There were 15 named storms this season, 8 hurricanes and 2 major hurricanes which was slightly above the normal numbers of 12 named, six hurricanes and two majors.  Many of the storms were long-lasting and this added to the “accumulated cyclone energy (ACE)” which factors intensity and longevity and it ended above the normal level for a typical North Atlantic tropical season. 

Storm tracks of all tropical systems in the 2018 Atlantic Basin tropical season. Source: NOAA

Storm tracks of all tropical systems in the 2018 Atlantic Basin tropical season. Source: NOAA

The 2018 hurricane season was actually expected to be quieter than normal due to an El Nino that was supposed to have formed by the summer, but it didn’t actually get going until later in the tropical season.  The tropical season actually got off to slow start during the spring and summer and there were no major hurricanes until Florence came along in mid-September.  Hurricane Florence peaked at category 5 status, but thankfully, weakened in the 48 hours before making landfall in North Carolina.  Despite the weakening of Florence before landfall, historic flooding was about to unfold over North Carolina as an “atmospheric brick wall” helped to slow it down to a crawl and the ultimate result was two to three feet of rain in southeastern sections of North Carolina.  Tragically, there were more than 50 deaths attributed to Hurricane Florence. 

The “accumulated cyclone energy (ACE)” value of 128.9 for 2018 is above normal for the North Atlantic. Source Colorado State University

The “accumulated cyclone energy (ACE)” value of 128.9 for 2018 is above normal for the North Atlantic. Source Colorado State University

Several weeks later, Hurricane Michael intensified rapidly in the Gulf of Mexico and then hit the Florida Panhandle at near category 5 strength (strong category 4).  Michael slammed the coast with 155 mph winds and a massive storm surge and is thought to be the most powerful storm to strike this particular part of Florida.  More than 40 people lost their lives during Hurricane Michael.  Only two other storms formed in the Atlantic Ocean, Nadine and Oscar, after Hurricane Michael ripped through the southern states. 

Meteorologist Paul Dorian
Perspecta, Inc.
perspectaweather.com