30 November 2020

The record-smashing 2020 Hurricane Season ends today

The 2020 Atlantic hurricane season officially ends today, and it has certainly been one for the record books.  As of today, there were 30 named storms, 13 of which became hurricanes, and 6 of those became major hurricanes (Category 3+ on the Saffir-Simpson Scale).  For context, the average of those same quantities over the past fifty years is 12.2, 6.3, and 2.5.

This also marks the end of my 25th year writing these updates on tropical Atlantic activity.  During that time, I have written approximately 1305 posts spanning 412 tropical cyclones, 190 hurricanes, 86 major hurricanes, and close to 50 retired storm names (2019 and 2020 TBD). I was honored to have been invited to write for the New York Times hurricane blog for four years, and then for the Washington Post's Capital Weather Gang from to 2012 to present.


The previous record number of named storms was 28, set in 2005.  And not only did 2020 beat that record, it did so quickly.  With the exception of the 1st, 2nd, and 4th storms, the remaining 27 were all the earliest formation dates on record! 

A common metric used to describe overall activity is the Accumulated Cyclone Energy, or ACE.  It is independent of the number of storms and their tracks, but essentially measures a cumulative intensity and duration of all storms.  14 of the 30 named storms were around for three days or less, and coincidentally 14 of the 30 never got stronger than a mid-range (50-knot) tropical storm.  So despite the large number of named storms, 17 of them were fairly short-lived and/or weak -- a handicap for generating a lot of ACE.  The 2020 season is in 10th place in terms of ACE, and is at 178% of an average season.


For the sixth year in a row, there was pre-season activity. 2020 came out of the gate strong, with Arthur and Bertha forming during May. Then Cristobal formed on the first day of the official season and it never let up after that.  A record ten named storms formed during September.  The regular list of 21 names was exhausted by mid-September, and the Greek alphabet was utilized for only the second time ever... beginning with Alpha on September 18 (which strangely enough was Portugal's first named storm landfall).  As of today, nine letters of the Greek alphabet have been used.

Two things stand out to me in that track map at the beginning of the post. The first is that only one hurricane (Teddy) existed in the tropics between the central Caribbean and Africa. That is not a trait we tend to think of with very active seasons.  The second is the high concentration of tracks in the western Caribbean and Gulf of Mexico.  I'm not exactly sure what caused this pattern, but some large-scale atmospheric/oceanic forcing was at work.  I don't think the weak La Nina alone explains this. Unfortunately, storms in the western Caribbean Sea and Gulf of Mexico almost always make landfall... there's no way out.

A record-breaking twelve named storms made landfall in the contiguous U.S., easily surpassing the previous record of nine set in 1916. Five of those twelve hit Louisiana alone, and three of those five were hurricanes (Laura, Delta, and Zeta). The Yucatan peninsula had three landfalls, including two hurricanes (Delta and Zeta), and then there's Nicaragua. Two Category 4 hurricanes made landfall at the same location (technically seven miles apart) just two weeks apart: Eta and Iota. Iota, a mid-November storm, became the season's strongest storm, rapidly intensifying to reach Category 5 status.  Not only was it the season's only Category 5 hurricane, it made 2020 the fifth consecutive year to have a Category 5 hurricane. November 2020 was the only November to have two major hurricanes.

Tracks of the landfalling tropical storms and hurricanes in the western Caribbean Sea and Gulf of Mexico during 2020.

Although the final reanalysis of the season won't be completed for a few more months, the preliminary track and intensity verification of forecasts made by the National Hurricane Center are shown below.  To arrive at these, all 24-hour forecasts are evaluated against all observed values at that time, and so on out to 120 hours.  The average error over the prior five seasons is included for reference. Overall, track forecasts were extremely close to the average out to four days, then slightly higher at five days (Paulette was a big reason for that drift at five days). Intensity forecasts were near-average out to two days then better than average for three, four, and five-day forecasts.


Of course, the bounds of the official hurricane season (June 1 through November 30) are arbitrary, and nature could still throw in more storms during December.  Years with post-season storms include 2013, 2007, 2005, 2003, 1984, 1975, etc. so it's certainly not unheard of; in fact, there have been sixteen known named storms to form during December since 1851, five of which became hurricanes.  The next two names would be Kappa and Lambda. Otherwise, the 2021 regular list will kick off with Ana and Bill.

Tracks of the 16 known storms that became tropical storms or hurricanes during December since 1851.

17 November 2020

Iota becomes Category 5 hurricane before landfall in Nicaragua

Enhanced satellite image of Hurricane Iota as it made landfall in Nicaragua on 17 November 0400 UTC.

From bad to worse... Category 4 Hurricane Eta made landfall in Nicaragua two weeks ago today, spreading catastrophic wind, flooding, and mudslides far inland through Central America. On Monday, Iota rapidly intensified to become the season's strongest hurricane, reaching Category 5 intensity just prior to making landfall in the same location as Eta. It "weakened" only slightly to a top-end Category 4 hurricane as the eye crossed the coastline early Tuesday morning. It's impossible to imagine two such hurricanes in two weeks at the same location. Iota will now dissipate over the mountainous terrain of Central America, dumping huge amounts of rain along the way. 


Iota was the only Category 5 hurricane of the 2020 season (so far), but it also claimed the title of being the latest Category 5 hurricane on record.  The one and only other candidate was in early November of 1932.  It also marks an unprecedented string of five consecutive years with Category 5 hurricanes in the Atlantic. This map below shows the tracks of the seven Category 5 hurricanes that have occurred over the past five years: Matthew (2016), Irma (2017), Maria (2017), Michael (2018), Dorian (2019), Lorenzo (2019), and Iota (2020).  Then there were ZERO from 2008-2015, then eight from 2003-2007. They definitely come in surges.


Unfortunately, there's a hint of another tropical wave right behind Iota, and there is some support for its development in the models -- the National Hurricane Center is giving it a 40% probability of forming later this week as it approaches Central America. This map shows a forecast of minimum surface pressures of trackable lows from the American GFS model ensemble on Friday, and that clustering of ensemble members near Costa Rica and Nicaragua is very troubling. Should this become a tropical storm, it would be the season's 31st and be named Kappa.


While the season continues to obliterate records for the number of named storms, the earliest formation date of the Nth named storm, and also for number of landfalls, it just now snuck into 10th place in terms of ACE (Accumulated Cyclone Energy).  ACE is a common metric used which basically accounts for overall intensity and duration, not the number of storms or where they go. The nine years that had more ACE are all very familiar to tropical cyclone enthusiasts: 1933, 1926, 2005, 1893, 1995, 2004, 2017, 1950, and 1961. It's fitting that 2020 now joins the top ten list.


15 November 2020

Hurricane Iota threatens recently-devastated Nicaragua

Since my previous update on Wednesday, the tropical wave in the Caribbean was upgraded to Tropical Depression 31 on Friday morning, then again to Tropical Storm Iota on Friday afternoon, making it the season's 30th named storm. On Sunday morning, it was upgraded to Hurricane Iota, the season's 13th hurricane.  The only other known season with 13 hurricanes was 2005 -- it ended up with 15.


Iota is tracking toward the west, which will bring it to northern Nicaragua in a couple days. You may recall that Eta just made landfall in this same part of Nicaragua on November 3 as a Category 4 hurricane; another Category 4-5 landfall only two weeks later is just unthinkable, but that appears to be exactly the situation. The wind, the flooding rain, the storm surge... all coming back to the same places in Central America. Unlike Eta, there is no indication that Iota will turn north out of Guatemala and head back over the western Caribbean.


Also, Eta made landfall in the Big Bend area of Florida on Thursday as a tropical storm, and Tropical Depression Theta is hours away from dissipating as a low-level swirl north of the Canary Islands. There are no other features of interest on the map right now, but when the time comes (and I'm sure it will), the next name on the list is Kappa.


To call the 2020 track map crowded would be an understatement. It's literally two seasons crammed into one, and it's not over yet.  While the official season spans June 1 through November 30, these hyper-active seasons tend to ooze out of those artificial start and end bounds.