30 November 2019

The 2019 Atlantic Hurricane Season comes to an end

Another hurricane season is in the books... and while the official season is six months long, the climatologically most active period can be narrowed down to a third of that: mid-August through mid-October.  This was year no exception to that, as 89% of the season's ACE was racked up during those two months.  The season ended with 18 named storms, 6 of which became hurricanes, and 3 of which became major hurricanes (Category 3+ on the Saffir-Simpson scale).

In terms of ACE (Accumulated Cyclone Energy), the season ended up at 129% of the average over the past fifty years.  Two storms, Dorian and Lorenzo, contributed an impressive 61% of the tally.

The season was dominated by a lot of weak, short-lived storms.  8 of the 18 named storms were of at least tropical storm intensity for two days or less!  The most destructive among them was Imelda, which was named for just six hours as it impacted parts of eastern Texas with nearly four feet of rain. Remember, "there's more to the story than the category!"

For the fifth year in a row, a pre-season storm jump-started things. Andrea was a subtropical storm that formed on May 20th and dissipated on the 21st.

By far, the most infamous storm of the season was Dorian, which stalled over the northern Bahamas as a Category 5 hurricane for nearly two days and gave south Florida a good scare as the monster storm refused to leave the area (see "The Unimaginable").

Hurricane Dorian on September 1, as it made landfall on Marsh Harbour. (CIRA/RAMMB)
It was the strongest hurricane to have ever impacted the Bahamas and tied the record for strongest hurricane landfall anywhere in the Atlantic (the 1935 Labor Day Hurricane was the other). It ended up following the curve of the southeast US coastline -- while the strongest winds remained offshore, significant impacts were still felt in Florida, Georgia, South Carolina, and North Carolina (but not Alabama).

I have the full-sized version of this radar loop and many others from Dorian at http://bmcnoldy.rsmas.miami.edu/tropics/radar/index.html#dorian19

Then later that month, Lorenzo became the easternmost Category 5 hurricane.  The third major hurricane was Humberto, which passed by Bermuda as a Category 3 hurricane on September 18.

A noteworthy void of hurricane activity in the track map at the top of this post is the Caribbean Sea and Gulf of Mexico.  Only Dorian and Barry were hurricanes in those areas, and for just a few hours each.

The final storm of the season was Sebastien, which stuck around as a tropical storm for a little over five days in the central Atlantic.  The last time a season reached the "S" name was 2012: Sandy.

Since I started writing and sharing updates on tropical Atlantic activity in 1996, I've written approximately 1,250 posts spanning 381 tropical cyclones, including 177 hurricanes, 80 major hurricanes, and 44 retired storm names. Thank you for your continued interest!  Next year's list begins with Arthur, Bertha, and Cristobal, and there are no new names being introduced since none were retired in 2014.

19 November 2019

Tropical Storm Sebastien forms with 11 days left in hurricane season

The disturbance that was east of the Leeward Islands for the past 7-10 days has finally developed into the 18th named storm of the season: Sebastien.  It is not a threat to land.  The last time we reached the "S" storm in a season was 2012 (Sandy).

As I mentioned in yesterday's post, Sebastien could easily be the 9th storm this season to last for two days or less, a remarkably high percentage of weak, short-lived storms.  With nearby dry air and strong vertical wind shear approaching by Wednesday, it won't be a named storm for long.

While the official hurricane season starts on June 1 and ends on November 30, nature does not always obey those artificial bounds -- so while this is likely the last storm of the season, we can't say for certain just yet!

18 November 2019

Disturbance near Leeward Islands could become 18th named storm

With twelve days remaining in the official hurricane season, the Atlantic may not have run out of steam yet.  A lingering low pressure system east of the Leeward Islands is getting better organized and could become the 18th named storm of the season this week: Sebastien.  It has been sitting nearly stationary for at least a week now in an area of very weak steering flow.  By the way, the last time we reached the "S" name in a list was 2012 (Sandy).

It's still not even a Depression, and as you can see in the satellite image above, it's not looking too impressive today. However, environmental conditions are marginally favorable today through Wednesday.  All models agree on a northwestward track, then recurve to the northeast as it gets picked up by a cold front.  It will not affect any land.

It only has a brief window of opportunity to develop before strong vertical wind shear comes along on Wednesday-Thursday and it transitions to a strong extratropical low pressure system.  This also means that if it develops and earns a name, it would be the *9th* storm to be named for two days or less this season! You read that right: if this forms and dissipates shortly thereafter, half of the season's storms (9 of 18) will have been a tropical storm or hurricane for two days or less.

Here is a map of the season's activity through today... if Sebastien forms it would be near where Karen dissipated in late September.  One feature that looks quite obvious on that map is the lack of activity in the Caribbean Sea and Gulf of Mexico.  Only Barry and Dorian were hurricanes in those two regions, and for a combined total of just a few hours, and both as Category 1 hurricanes.