15 August 2018

'Season of Slop' continues as Subtropical Storm Ernesto forms

Early Wednesday morning, a formerly-non-tropical low pressure over the north central Atlantic acquired subtropical characteristics and was upgraded to Subtropical Depression Five, then to Subtropical Storm Ernesto six hours later. In location, structure, and appearance, this is almost a duplicate of Debby last week.

In the satellite image above, note the smoke to the north and west of the storm and getting wrapped into the circulation... with the aid of backward trajectory analyses, I confirmed that the smoke originated all the way from the fires in the western U.S. about five days ago!!!

My phrase "season of slop" refers to the abnormal abundance of subtropical activity -- Alberto was subtropical for its entire life, Beryl was subtropical for the second half of its life, Debby was subtropical for its first day, and now Ernesto is subtropical.  So far only Chris was purely tropical, yet ironically spent its entire life in the subtropics!

Ernesto is in a favorable environment for some additional strengthening in the short term, but by the end of the week it will be over much colder water and transitioning to an extratropical cyclone as it zips off toward the northeast.

    Ernesto is a name from the original six lists, and its first appearance was in 1982. This is the name's 7th incarnation, and only the two most recent (2006 and 2012) became hurricanes.  The 2006 version hit the southern Florida peninsula as a tropical storm and the 2012 version hit the Yucatan peninsula as a Category 2 hurricane.

    07 August 2018

    Subtropical Storm Debby forms in far north-central Atlantic

    The fourth named storm of the 2018 Atlantic hurricane season, Debby, has formed about 1000 miles west of the Azores.  It has been a persistent mid-to-upper-level feature for about a week now, just drifting around, but it finally established a surface circulation and strong enough winds to earn an upgrade to a subtropical storm.  Note that as of now, it lacks the structure to be a fully tropical system. However, its time will be very limited -- it will pass over increasingly cold water and get absorbed into an approaching trough within a couple days.

    Debby is the third storm this season to be subtropical... Alberto began its life as a subtropical cyclone on May 25th, and the second half of Beryl's life was subtropical.  Climatologically, the 4th named storm forms on August 22, so Debby is about two weeks ahead of par.  In terms of ACE (Accumulated Cyclone Energy), the season is at 145% of average for this date.

    Aside from Debby, the Atlantic is quiet.  This time of year, we start looking to Africa for incipient waves/disturbances, but the water temperature in the deep tropical Atlantic between Africa and the Lesser Antilles remains cooler than average, which will be a suppressing factor for tropical cyclone activity there for a while.


    11 July 2018

    Hurricane Chris accelerating into north-central Atlantic

    Since yesterday's update, Chris reached a peak intensity of 105 mph... not quite Category 3 intensity.  As of the 11am EDT advisory on Wednesday, the peak sustained winds have fallen to 100 mph, which is still a Category 2 hurricane.  It's also zipping off to the northeast at 22 mph, not too shabby considering it was parked for four days.

    Chris will transition from a tropical to an extratropical cyclone on Friday as it passes over colder and colder water and interacts with a mid-latitude trough. But, Newfoundland will likely experience hurricane conditions on Thursday before it makes its exit. You can watch it cruise through that area via a series of radars on Nova Scotia and Newfoundland: https://weather.gc.ca/radar/index_e.html?id=ERN

    [By the way, Chris is a name from the original set of six rotating lists... first used in 1982.  Among its six previous incarnations, the highest intensity reached was 75 kt in 2012, so the 2018 version now holds that title.]

    Looking at the seasonal activity to-date, we have had 3 named storms, 2 hurricanes, and 0 major hurricanes, with an ACE (Accumulated Cyclone Energy) of 12.1.  An "average" season would have 1 named storm, 0 hurricanes, 0 major hurricanes, and an ACE of 3.7 by now.

    So in terms of ACE (a commonly-used metric that combines the intensity and duration of all storms), we are at 326% of normal activity for the date.  In other way to frame it is that the ACE is currently what it climatologically would be on August 14. And as I mentioned yesterday, the last time we had two hurricanes so early in the season was 2005.

    Ex-Beryl is centered over the central Bahamas and is not getting any better organized. Models have backed off on re-developing this disturbance, but it may have a brief resurgence as a subtropical cyclone over the weekend off the New England coast -- nothing to be concerned about.