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.

    10 July 2018

    Chris upgraded to a hurricane, and has barely moved in four days

    Chris is officially the season's second hurricane as of Tuesday afternoon, and it's perhaps slightly disconcerting that the last time there were two hurricanes so early in the year was the infamous 2005 mega-season (Cindy and Dennis).  Climatologically, the second hurricane forms on August 29, so this is 50 days ahead of par.

    Peak sustained winds have jumped up to 85 mph, the central pressure has fallen to 980 mb, and it is finally moving to the northeast at 10 mph. Tropical storm force winds extend an average of 80 miles from the center.  Due to a stagnant atmospheric steering pattern, Chris is located just 100 miles from where it formed last Friday... right off the North Carolina coast!

    Center positions of TD3/Chris going back to when it formed on July 6.
    Chris will continue to intensify as it picks up speed and heads northeast into the north-central Atlantic. It will impact Newfoundland overnight on Thursday, then head over to visit Ireland and the British Isles on Sunday-Monday as a potent extratropical cyclone.
    Meanwhile, we still can't completely dismiss the remnants of Beryl.  Currently centered just north of Hispaniola, the disorganized blob of thunderstorms will pass over the Bahamas tonight and encounter an environment more favorable for regeneration on Wednesday-Thursday.  Even if it does regain tropical cyclone status, it is not expected to affect land at all after departing the Bahamas.

    06 July 2018

    Surprise! Beryl becomes season’s first hurricane

    An update on very-tiny Hurricane Beryl (and there's potential for something to form near the Carolinas in a few days) can be found on the Capital Weather Gang blog:

    Surprise! Beryl becomes season’s first hurricane

    31 May 2018

    As hurricane season begins, Colorado State lowers its prediction for the year

    Today's post highlights the updated seasonal hurricane forecast from the pioneers of the science, Colorado State University... and formally introduces the names and products of the 2018 season (Alberto was a sneak peak!).

    As hurricane season begins, Colorado State lowers its prediction for the year

    30 May 2018

    27 May 2018

    Severe impacts from Subtropical Storm Alberto beginning in Florida and parts of the Southeast

    Subtropical Storm Alberto is strengthening, and impacts are spreading to more areas.  Landfall is still expected on Monday morning. My Sunday morning update is available on the Capital Weather Gang blog:

    Severe impacts from Subtropical Storm Alberto beginning in Florida and parts of the Southeast

    25 May 2018

    Subtropical Storm Alberto forms, kicking off hurricane season 1 week early

    On Friday morning, the tropical disturbance we have been watching for what seems like forever was upgraded to Subtropical Storm Alberto, the first named storm of the 2018 Atlantic hurricane season.  It also makes 2018 the 4th consecutive year with a pre-season named storm, an unprecedented string.

    Alberto is expected to transition to a fully tropical storm later, but as of now it does meet the criteria.  The difference between the two is really just academic, as it pertains to the structure of the system... not the impacts. If and when it becomes Tropical Storm Alberto, nothing will be magically different about it, other than the distribution of the wind field and perhaps the symmetry of the thunderstorms around it.  Cyclones come in many shapes and sizes across a spectrum!

    Just as before it was named, the biggest impact will be extremely heavy rain over a large region.  The forecast 5-day rainfall totals are shown below:

    Secondly, storm surge flooding will become a concern along Florida's west coast and along the northern-to-northeastern Gulf coast.

    Models remain in pretty good agreement on the track and timing, but with any tropical cyclone, it's big, so impacts will extend far beyond the center line.  A series of 3-day track forecasts from dynamical models is shown below.  Wind shear should keep the system lopsided, so the messier, rainier side will be to the east of center, including the Florida peninsula.

    Stay tuned to the National Hurricane Center website for the latest forecasts, watches, and warnings.

    It is interesting to note that since 1851, only 3 other tropical cyclones formed within 200 miles of where Alberto is now during May (plus one in February 1952). All three May ones formed on May 31st!

    24 May 2018

    2018 likely to be 4th consecutive year with pre-season named storm: Alberto

    The tropical system I mentioned in last Friday's update is indeed getting better organized in the western Caribbean.  Many models have been showing this for at least the past 10 days, so it comes as no surprise. As of Thursday afternoon, the system is centered inland over the eastern Yucatan peninsula and is tracking toward the north.

    If this earns a name this weekend, which seems likely, it will be the unprecedented *4th* consecutive year with a pre-season named storm!  The first name on this year's list is Alberto.  (and coincidentally, the last time Alberto appeared in 2012 it was also a pre-season storm!)

    Models have come into rough agreement on the track and timing of this potential tropical cyclone, but they still have differing opinions on the intensification.  Invest 90L, or "pre-Alberto", will head north through the central-to-eastern Gulf of Mexico this weekend. Water temperatures ahead of it are in the 27-28°C ballpark (80.5-82.5°F), which is plenty warm to fuel a tropical storm or a hurricane.

    The system is embedded in a very moist envelope, so dry air wrapping into to the circulation shouldn't be an inhibitor. The biggest obstacle facing this nascent cyclone is vertical wind shear.  But even that may not be enough to stop it from intensifying by Saturday.  As of now, models agree on a Monday morning landfall as a strong tropical storm or possibly even a hurricane... somewhere between eastern Louisiana and the eastern Florida panhandle. The exact location doesn't matter though, as impacts extend far from the center.

    Unfortunately, it's hard to trust the intensity details too much yet since it's currently not even a Depression. But as time goes on (and it escapes the influence of land), confidence in the model guidance will increase.

    By far, the biggest concern associated with this is flooding caused by heavy rainfall.  Not only is very heavy rain expected in the northern Gulf coast region near the landfall location, but also over south Florida and up into Georgia and South Carolina in the coming week.

    Depending on just how much this strengthens, the second-order concern will be storm surge along the west Florida coast and northeastern Gulf coast, so stay tuned!

    On the topic of another pre-season named storm, I plotted up the formation date of the first named storm from the past 40 years.  A very obvious trend appears!  There may be a few reasons for this, but it's certainly interesting.

    18 May 2018

    Can't wait for hurricane season to start? You may not have to.

    I have a brief update on a potential development in the western Caribbean Sea which could affect Florida next Friday-Saturday... it is available on the Washington Post's Capital Weather Gang blog:

    Hurricane season technically starts June 1, but it could fire up early

    12 April 2018

    Four names retired from 2017 hurricane season, the most since 2005

    In a recent meeting of the World Meteorological Organization (the agency that decides on tropical cyclone names), four names were retired from the 2017 list: Harvey, Irma, Maria, and Nate.  There is a series of six name lists that rotate every six years, so the same list we had in 2017 was also in place for 2011, 2005, 1999, etc, and will be used again 2023.

    However, names can be permanently retired from use and replaced with different ones if the storm associated with that name was "so deadly or costly that the future use of its name on a different storm would be inappropriate for obvious reasons of sensitivity" (NHC). The new names in the 2023 list will be Harold, Idalia, Margot, and Nigel.

    2017 was impressive in that more than three names were retired from a single season... the other such seasons were 2005 (5), 2004 (4), 1995 (4), and 1955 (4).

    Irma was retired on its first time on a list (it replaced Irene from 2011).  The other names that were retired on their list debut were Igor (2010), Ike (2008), and Michelle (2008).  [Note that Joaquin first appeared on a list in 2009, but did not get used... it was retired after its first use in 2015.]

    Having yet another retired "I" name amplifies that letter as the most commonly-retired (11 times)... "C" is in second place at 9 times.

    And, not surprisingly, the most frequent month for a retired storm name to have occurred in is September.

    Finally, although Category 5 storms are the strongest, they are rare... so the majority of names that get retired are from storms that peaked at Category 4 intensity.  But, notice that "major hurricanes" (Category 3 or higher) account for 84% of all retired names.

    05 April 2018

    April outlook for 2018 Atlantic hurricane season activity

    As they have done every year since 1984, Colorado State University (CSU) has released their initial predictions for the upcoming Atlantic hurricane season. Phil Klotzbach and I take a look at the numbers in this post on the Washington Post's Capital Weather Gang blog: