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May 2013

Thursday Evening Atlantic Tropical Outlook

   Posted by Levi at 1:25am on May 31, 2013

The pattern remains active and wet across the western Caribbean Sea, Bay of Campeche, and much of central America. The region continues to be under the influence of large-scale upward motion associated with the convective peak of the MJO wave, which is forecasted to continue as the GFS and ECMWF evolve the MJO index into phases 1 and 2 during the next 10 days. It is under this regime that Hurricane Barbara formed in the EPAC and quickly moved ashore over Mexico. Her remnant circulation now resides over the Bay of Campeche, and is no imminent threat for tropical development, though her remnants may serve as a focus point for the development of the monsoonal gyre over central America in a few days.

Over the last few days, it has become clear that the GFS and GEFS overestimated the strength of the large-scale ascent in this region of the world. Although the MJO is at a favorable position for upward motion, the subsident portion of a Kelvin wave is moving into the eastern tropical Pacific, which may largely counter-balance the MJO. However, both the GFS and CMC ensemble means indicate that the greatest region of sinking associated with this Kelvin Wave will set up very near the equator just west of Columbia, eventually moving into northern South America next week. This setup is supported by the recent cooling of the Nino 3 ENSO region, and would result in an enhanced poleward low-level flow, supporting the monsoonal southwesterlies into central America. This, in combination with the enhanced phase of the MJO acting at higher latitudes, along with a mid-latitude trough passing through the Tennessee valley in 3 days, will lead to a northward displacement of the monsoon trough.

A convergent belt of trade wind flow has set up in the southwestern Caribbean in response to the already enhanced monsoonal pattern, and current model guidance shows this continuing well into next week, with weak perturbations running southeast to northwest out of the ITCZ through this zone. These waves, along with the large-scale forcing at work, will act to facilitate the development of a monsoonal gyre sometime early next week, likely in the vicinity of the Yucatan Peninsula based on the latest model guidance. The operational GFS and CMC have periodically portrayed a weak tropical cyclone developing within this gyre and lifting northward into the Gulf of Mexico, though the CMC is characteristically way too fast and too strong. The ECMWF has recently tended towards this solution, with the most recent 12z run today depicting a tropical storm moving into New Orleans at Day 10. With the expected exception of the CMC, the global models have come into reasonable agreement during the last day or two on the timing and placement of the disturbance which could spawn such a storm mid-late next week, but with the time frame still being 6-8 days, and the time of year being early, there cannot be any degree of confidence attributed to tropical development at this time. However, in light of the rather favorable setup for an active monsoon, and the very low pressures being forecasted over the Gulf of Mexico by the GFS and ECMWF ensemble means after Day 6, the possibility for an early Atlantic tropical cyclone will have to be watched carefully if forecast trends continue during the coming days.

Regardless of whether tropical development becomes a significant concern, the pattern will remain a wet one for large portions of central America, the western Caribbean, the western Greater Antilles, and the Bahamas as large-scale upward motion and a convergent trade wind flow enhance convection in the region through next week. Should there be an attempt at tropical development, associated heavy rainfall will likely spread northward into the eastern Gulf of Mexico and southeastern U.S., as the mid-latitude flow is expected to be far enough south to eventually catch any disturbance that moves north of 20°N or so. However, this would occur in 6+ days from now, and cannot be predicted with specificity until/if a tropical disturbance forms.




  • Boyroy says:

    Great job, as always, Levi!

  • drdave420 says:


    Great as always, but I have no video link in either of the last two blog entries.

    Is your post text-only for technical reasons? Cannot find a recent post on Youtube, either.

    Your videos are great, so if you have time and resources, would love to see another one soon.

  • harrycane says:

    Great job Levi once again. It seems when I listen to your videos and read your blogs, it gives me insight into what the general media will report sometimes days or weeks later. You now are my source for tropical information. Sometimes I feel the NHC tries to keep people guessing as to what is on the horizon. The very fact that they don’t want to show people computer models of approaching storms bothers me. I am guessing they feel we can’t handle that stuff and we will over react to outlier models. It blew my mind when you talked about twin cyclones in the Indian Ocean and how that will effect us. Jeff
    Masters mentioned the same about a week later. Let me say I live in South Florida and I can say your forcast was spot on around us. As you said, last week in May and into June, the moisture would set in from the MJO. You have the knowledge and the ability to convey thoughts very well. I don’t know what your major is but if it’s not weather you may be missing your calling. I don’t mean to sell you short, you are most likely good at whatever you tackle!! Thank You Again, Regards, Dave J

  • Jefiner says:

    As always, thorough and thoughtful. Thank you, Levi!

  • nick says:

    Hi Levi once again thank you for your update very intresting.Just one question do you think they will be alot of dust and dry air and sheer this season like last season after seeing some of the storms last season they did seem to struggle with the dust,dry air and sheer could this be a factor this season also?

  • Daniel says:

    Thanks Levi. I don’t understand half of what you said but I love absorbing the info. Keep up the great work!

  • scottsvb says:

    Good Job Levi…you were cautious on anything developing after 5 days till we see more model runs. Videos start June 1st?

  • HuricaneHunterJoe says:

    Great job on your website Levi! Always get good information in a understandable manner. Hope ya find time to come visit Doc Masters Blog.

    Im looking at all the long range models…….GFS,CMC,NOGAPS AND EURO all showing anything fro super hurricane( to tropical storms at 168-180 hours…..these were the 5-31-2013 1200z model runs…does the fact that all the models are in agreement on having some kind of storm in the eastern gulf of mexico add any weight to their forecast accuracy at that time frame(6-7days out)? Or would you ignore that as being too far out in time?…As always thanks for all the great info ! HH Joe

  • Eric Webb says:

    Hi Levi, great post by the way, you are my personal favorite when it comes to tropical cyclone prediction and I always learn something new in your posts and videos, so please keep them coming! I thought you might want to see this, just out of pure curiosity, I looked to see if I could find a relationship between this current pattern set-up & the PDO, AMO cycles, and indeed it appears I may have stumbled upon something very interesting. I’ve actually discovered that in looking at past instances where storms come out of the deep Caribbean and move north-northeastward to affect the southeastern US and the eastern US during the month of June actually has a correlation to PDO & AMO flips. For instance, I think many of us have heard many times, especially in Joe D’Aleo’s posts how the PDO flipped into its cold state in the mid-late 2000s, and when you look at those years during that PDO flip, it is interesting to see a collection of storms that came out of the deep Caribbean during the month of June and went onto affect the southeastern and eastern US. Arlene (2005), Alberto (2006), and Barry (2007). Also, need to mention Tropical Storm Bill (2003), which also came out of the deep tropics in June to affect the eastern US. Further evidence of a possible link to PDO & AMO flips to this type of pattern where tropical systems come out of the deep Caribbean and affect the eastern US during the month of June is also evidenced by Hurricane Allison (1995) and Tropical Storm Alberto (1994), which correlate very nicely with the flip to the warm AMO that began in 1995. Tropical Storm Alberto in 1982 is also the “lone ranger” so to speak of the 1980s, and this occurred during the early 1980s, not long after the flip of the PDO into its warm cycle that occurred around 1979. Another interesting revelation is the barrage of storms that come out the deep tropics and affect the eastern US during the month of June in the 1960s and early 1970s, when there are actually was a few flips in the AMO. The AMO, which had been predominantly warm during the 1930s-50s flipped into its cold cycle in 1964, and this was followed by 3 tropical cyclones that formed out of the deep tropics during the month of June and affected the eastern US, including Unnamed (1964), Unnamed (1965), and previously mentioned hurricane Alma in 1966. Then, in the very late 1960s and going into 1970, the AMO briefly flipped into its warm cycle, and to no surprise, a few other tropical systems formed out of the deep tropics and affected the eastern US during the month of June including Abby (1968) and Agnes in 1972. In conclusion, the formation of tropical systems out of the deep tropics and moving north-northeastward during the month of June to affect the eastern US seems to have a correlation to periods in which there are major flips in either the PDO or AMO. This is interesting given the current forecasts for tropical cyclone development to originate from the deep tropics and move north-northeastward affect the eastern US next week, as this would seem to suggest given the evidence presented above in my posts, that perhaps we are on the edge of yet another major flip in the PDO or AMO, and if this indeed true, perhaps looking at tropical cyclone development coming out of the deep tropics during the month of June and affecting the eastern US is a factor that needs to be analyzed and studied as it would help to better understand the relationship of tropical cyclones and the PDO, AMO, plus offer as a guide to indicate overall future climate trends that are a result of changes in PDO & AMO.

  • Mech 70002 says:

    Great information. Thanks for the hard work. Please keep it up!

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