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May 2013

Wet Start to June Likely for W. Caribbean Region – Potential for Tropical Development

   Posted by Levi at 7:12pm on May 25, 2013

The weather pattern is likely to turn very wet by the end of the month and into the first week of June for the western Caribbean and greater Antilles. The GFS and ECMWF are finally in agreement on the timing of large-scale upward motion associated with the MJO moving over the Caribbean during the next 5-15 days. We have already been discussing this event during the past few weeks, as the twin tropical cyclones in the Indian Ocean during the first week of May yielded a clue that the MJO would likely end up in our area of the world by the end of the month. The GFS was originally too fast with this event, bringing upward motion over the Caribbean by May 23rd. The correction for the fast bias of the GFS seems to be on its way to verifying, as the GFS and ECMWF ensembles now lower pressures and increase precipitation in the western Caribbean during the target period of the final days of May and the first week of June, as anticipated since early May. Now that these two models agree on the general evolution of the pattern, confidence is high in an intrusion of the central American monsoon circulation into the western Caribbean in several days.

The overall pattern over North America is also likely to facilitate the development of low pressure in the western Caribbean during the first week of June. The image below depicts the average MSLP anomaly forecast for the first week of June from the GFS ensemble mean. As large-scale upward motion invades the Caribbean, anomalously high pressure is forecasted to simultaneously build over the eastern United States, a response to a positive arctic oscillation and negative PDO-type pattern. This setup with low pressure in the Caribbean and high pressure to the north means that air is forced to converge (pile up) and rise in the Caribbean, further strengthening the low pressure area. This will likely result in a large area of heavy precipitation developing from central America through the greater Antilles and even into the Bahamas and southern Florida. Such a pattern is also conducive for the formation of a tropical storm, though such an event cannot be forecasted with confidence this far in advance. More details will become available once the monsoon circulation materializes and we are able to physically track it.

Overall, the wet pattern for the western Caribbean region that has been advertised over the last few weeks for the end of May and the beginning of June is coming into focus on the models, and is now within the 10-day forecast period. The GFS operational is now showing a 1004 mb low north of Honduras in 8 days. While details of the possible tropical storm formation cannot yet be known, the potential that we have been talking about still exists, and is now moving up the timeline on the model forecasts. Whether or not tropical formation occurs, the medium-long range forecast is confident in a very wet pattern invading the western Caribbean and greater Antilles islands by May 29th, likely lasting through the first week of June. Once this event begins and the monsoon circulation develops, we will be able to properly assess the potential for tropical development.

We shall see what happens!




  • Mech 70002 says:

    Thanks for the information. Looks like things are coming together for the early part of the season. We all appreciate your hard work. Please keep it coming this (busy) season…

  • Dave says:

    With lows developing in the warm ocean to the south of Cuba and high pressure building over the eastern United States, would that make any storm that tries to develope head west to Mecico or Texas?

    • Levi says:

      That’s pretty unlikely, unless the storm forms in the western Gulf of Mexico to begin with. Early in the season, mid-latitude troughs still reach far enough south to bring almost anything to the north or northeast fairly quickly, without allowing for much westward movement. I know that can seem counterintuitive at times. The high pressure you mention will likely help the storm form (if one forms), and then move out of the way and allow it to move north somewhere.

  • roatangardener says:

    finally got some rain last night after 2 1/2 months of nothing here on Roatan (Honduras) guess it is the beginning of your forecast for increased rain in the western Caribbean. thanks for a great site.

  • Belizeit says:

    Thank you for the update Levi we here in the west Carribean have been waiting for rain and now its starting slowly but surly.

    How was your trip to the humid and hot Oklahoma ?

    • Levi says:

      I’m still here! I’m here for most of the summer. It’s already suffocating heat, but it will be 20 degrees hotter in 4-6 weeks. I don’t know how I will bare it, but this experience is worth it!

      • Belizeit says:

        You will get used to it just as the rest of us i live in the tropics and weather is unpredictable heat indexes can be over 100F any day of the year. But one thing that we have diffrent is we never have long days and the nights are ussually cool around 75F.

        • Levi says:

          You see, even 75°F is too hot for me, especially with a 70°F dewpoint lol.

          • Belizeit says:

            lol i know what you mean i was in canada once and for people there it was normal but my hard backed skin has no lard to keep me warm .

  • nick says:

    hi levi thank you very much for all your hard work and giving us info that we can understand im just wondering if the forecast is the same as previous blog will the storms have more of a west track this season to previous season where they tracked more north my parents are in florida

    • Levi says:

      My seasonal forecast from March hasn’t changed. I still think the eastern/northern Caribbean islands and the eastern seaboard will have the most elevated landfall risk relative to normal this year. That includes Florida. Anybody can get hit in any year, and Florida gets more hurricanes than any other state, so be prepared.

  • Papi says:

    Thanks. Well done as always.

  • nick says:

    thank you very much levi keep safe :)

  • daddyjamesb says:


    When do you think that the shear will drop in the GOM/Carribean enough that we should be seriously concerned that something would develop?

    If this is suffocating heat, I am worried for you in 4-6 weeks when it will be truly stifling heat. Hopefully you’ll be acclimated by then. Then again, when you return home, you’ll be freezing cold . . .

    Admire your work ethic . . . hope that things are still going good here in OK.


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