• Irma track: Beware of more adjustments in hurricane path models

    By: Michael Buresh


    SEPT. 7 UPDATE: Irma headed for Southern Bahamas

    Mandatory evacuations for Florida, Georgia counties

    Gov. Scott: Floridians on both coasts should prepare for evacuation

    Good deal of uncertainty continues regarding the final path of Irma in the long range.... models shift now to the east as a whole... track forecast - for the moment - shifted east too....  Hurricane WARNING Northern Lesser Antilles, Virgin Islands, Puerto Rico & SE Bahamas... hurricane WATCH Dominican Republic.... tropical storm "Jose" develops over Central Atlantic....

    The "Buresh Bottom Line" is: stay tuned!... Always be prepared!..... City of Jacksonville Preparedness Guide... Georgia Hurricane Guide.  It is still too early to pinpoint local (Jacksonville/NE Fl./SE Ga) impacts, but I am rather certain - higher than 50% - that there will be at least some impact Sunday into early next week in the form of heavy rain, strong onshore flow & winds/possible storm surge & isolated tornadoes.  The exact magnitude of which I will outline as my confidence in the track grows.

    According to the NHC Wed. morning: "The eye of Irma passed over Barbuda, St. Barthelemy, and St. Martin this morning, and will be moving over portions of the British and U.S. Virgin Islands shortly. A NOAA National Ocean Service observing site on Barbuda measured sustained winds of 103 kt with a gust to 135 kt earlier this morning before the anemometer failed. The station also reported a minimum pressure of 916.1 mb. A minimum pressure of 915.9 mb was reported on St. Barthelemy."

     "Irma" remains a classic deep tropics long track (trans-Atlantic) hurricane. Changes in structure (eyewall replacement cycles) from time to time will lead to fluctuations in intensity but Irma - overall - should remain a major hurricane into the weekend.  Satellite imagery shows a well developed hurricane with a clear eye & excellent outflow over the top.  NOAA hurricane research planes are flying through (avg. 1,000-10,000 feet) & around "Irma" pretty regularly which will give us a better idea of the structure & intensity & - above all - hopefully add to some consistency & accuracy in model forecasts assuming better analysis/input for the models.

    Some of the plane recon is being used in the model & might be part of the reason for the recent big track adjustments by the models.... in addition to it being quite clear that a big trough moving into the Eastern U.S. will miss "Irma" (more on that below).  And this from the NHC:

    "Six hourly upper-air soundings over the central United States will better sample the upstream mid-latitude trough. In addition, the NOAA G-IV aircraft will begin sampling the environment around Irma this afternoon and evening, and these data will be included in tonight's 0000 UTC model runs." [00Z = 8pm EDT.... Central U.S. sounding sites: Bismarck, Dodge City, Amarillo, Topeka, Oklahoma City, Springfield, Detroit, Minneapolis, Rapid City, North Platte, Aberdeen & Omaha... + extra soundings from San Jaun, Puerto Rico."

    I cannot emphasize enough that it's too early - & would be premature & irresponsible - to try to peg exactly 
    where Irma is going to go in the long run &, therefore, it's still early to determine which parts of the U.S. might 
    be adversely impacted.  It's looking more & more like the Bermuda high over the Atlantic will hold strong enough to near the Florida Straits/SW Bahamas before turning NW then north.  Most likely closest approach to Fl. will be over the weekend into next week.  Stay cool, calm & collected... NOW is the time to prepare:

    (1) peak of the hurricane season is upon us

    (2) you'll be prepared for anything mother nature throws at us - hurricane, lightning, flooding, tornadoes, etc.  Preparations do not need to take a long time nor do preparations need to be expensive.  But preparing now will offer peace of mind for when & if a storm is headed your direction & will also give you a better chance to survive the storm then allow you thrive after the storm.

    (3) know your evacuation zone

    Forecast models continue to jump around though have - as a whole - shifted back to the east! The GFS, European & - finally -  now the UKMET are sensing the weakness over the Eastern U.S. which Irma is likely to follow - the million dollar (literally!) question is when & how much.  More adjustments & changes are ahead - it would be prudent to not hang on each & every individual model run but rather look at the bigger picture in the coming days.  The mountainous terrain of Cuba still might come into play but not for long, if at all.  And any building/movement &/or strengthening of the Bermuda High - which has been a strong mainstay for months - makes full storm recurvature more difficult - this is a sentence have had in this blog since early last week & is obviously now coming into play.  

    A rather deep upper level trough will move into the Central/Eastern U.S. through Fri. which will play a pivotal role in the eventual movement of "Irma" (that's why extra soundings are being released in the Midwest).  The GFS model upper level (500 mb) chart below for Sun., 09/10 shows the strong trough lifting out far to the north & not picking up Irma but still leaving behind the clear alleyway along the U.S. east coast.  As the trough lifts out, a strong surface high will build into the Northeast U.S. which will block Irma from getting too far north while an upper level ridge builds underneath the departing trough.  This puts the coastline from Fl./Ga. to Virginia on high alert!.... with a move that would be very near if not into Florida & quite possibly close to Jacksonville at one time or another.  And by no means is this set in stone! 

    The GFS model is now leaning east of Fl. then into the Carolina's (Matthew-esque) & now the European is pretty close but a little slower. The UKMET takes Irma over Cuba for a time before abruptly turning north.... though the model has had a slight southern bias on Irma so far.  I still believe a rather abrupt turn to the north will occur in the long run.  The question becomes when & where.   But it is clear - to me - the big eastern U.S. trough will be fast moving & transient & that "Irma" does not get sucked up into the trough & taken far to the east over the Atlantic.  In other words, no escape route & the question is what part of the U.S. coast line is most at risk.


    STILL VERY EARLY on exactly how the steering currents will play out by the weekend into early next week as "Irma" makes its move W/NW then more northward.  Global models will continue to try to correct for the better part of the next several days, especially given the analysis data provided by hurricane hunter & research aircraft.  A combination of plots from each model's run (ensemble) points to near Florida by the weekend/early next week but with any part of the U.S. coastline potentially at risk for a landfalling hurricane.  I cannot emphasize enough the uncertainty at this point.

    People have been asking about a "way out" - where Irma doesn't impact Florida at all ... or even the U.S.  While that seems unlikely, there are 2 possibilities that aren't off the table:

    (1) land interaction with Dominican Republic/Haiti &/or Cuba

    (2) the upper level high pressure ridge bridges between the Bermuda high over the Atlantic & the Southwest U.S. This would really have an impact keeping Irma on a much more westerly or even southwesterly path.  Not likely.  And while the move east might spare some of Fl., a hit on the U.S. east coast remains highly probable.

    Upper level (500 mb) chart below from GFS for early Sunday:

    "Irma" model plots - yet another big shift!....

    Fascinating imagery(!) from CIMMS, University of Wisconsin, Madison - Microwave radar-simulated imagery showing Irma wrapping up... click here for full definition..... as "Irma" rapidly tightens up then weakens....

    "Jose" to the east/southeast of "Irma"... & "Katia" Western Gulf of Mexico....

    Very warm ocean water ahead for Irma:

    Even more telling - the oceanic heat content showing a wealth of deep warm water over the SW Atlantic/Caribbean & Gulf of Mexico:

    And let's dust off our Pacific typhoon teleconnection for trying to forecast "Irma" - it's not quite exactly lined up but is becoming close enough to possibly draw some parallels.  The 500mb chart below from the GFS for the N. Pacific to the Northern U.S. shows trough, ridge, trough, ridge, trough - the last trough being over or near the Eastern U.S. (it's what's picking up the "Harvey" remnants).  The W. Pacific trough is picking up typhoon "Sanvu" keeping the tropical cyclone very near or to the immediate east of Japan with a recurve into the N. Pacific.  This MIGHT be - & so far has been -  an early clue that at least some semblance of troughing or alleyway will remain in place over or near the Eastern U.S. which COULD draw Irma northward near or over U.S. coast.


    Satellite imagery below shows a band of clouds over the Eastern U.S./W. Atlantic - a weakening front that will be reinforced over the next couple days & is part of the weakness in the upper level flow that gradually tries to pull Irma northward....


    .... will soon become a hurricane & then languish in the "backwash" of Irma for many days.  I'm still not certain this simply stays out to sea & bears watching in the long run - 10-14 days - for a possible loop then turn more to the west.  At least a brush with the U.S. east coast is not out of the question as an upper level ridge rebuils underneath Irma & to the north of "Jose".


    The 11th named storm of the season has developed over the far W. Gulf of Mexico.  A strong upper level ridge over the Western U.S. should be the primary guiding influence on Katia pushing the storm more southeast then eventually west into Mexico - possibly as a hurricane(!).  No impacts for the U.S. as it stands now & no additional widespread significant rain for Texas or Louisiana from Katia.

    East Atlantic IR satellite:

    Mid & upper level wind shear (enemy of tropical cyclones) analysis (CIMMS):

    The main development region (MDR) shows above avg. temps. - in fact - only 2005 & 2010 were warmer.  The deep warm ocean water can "energize" tropical cyclones:

    SE U.S. surface map:

    Surface analysis centered on the tropical Atlantic:

    Surface analysis of the Gulf:


    Next Up: