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July 2017

Tropical Storm Don Forms – Will Impact Windward Islands Tuesday

   Posted by Levi at 12:54am on July 18, 2017

Tropical Storm Don has formed east of the Windward Islands. A small circulation formed within a broad trough Monday afternoon, identified by an Air Force reconnaissance mission. The recon plane found winds of about 45 mph as of the 8pm AST NHC advisory. While the circulation was originally associated with only limited convection, a strong convective burst has formed over the center of the system during the last few hours. Whether this burst is strengthening Don or not will likely be hard to tell until the next recon mission Tuesday morning. Given the small size of Don’s circulation, the storm could easily strengthen or weaken in a short period of time. Environmental conditions ahead of Don are favorable in the short term, with SHIPS diagnostics indicating that shear will remain below 10 kt until Tuesday evening, and Don’s circulation is still isolated from the dry SAL air mass to the north. Thus, it would not be surprising to see some intensification of Don on approach to the Windward Islands on Tuesday, but the official NHC forecast from Monday evening expects little strengthening for now. A Tropical Storm Warning has been issued for Grenada, and Tropical Storm Watches for St. Vincent and the Grenadines, Barbados, and St. Lucia. After entering the Caribbean, Don’s small circulation will likely struggle to maintain itself within strong trade winds north of South America, and weakening and eventual dissipation is expected by late Wednesday. However, tropical storm conditions could potentially impact some southern Caribbean islands before that occurs. Please see the latest NHC advisory at for the latest watch and warning information.




  • Bud says:

    Thanks Levi,
    Keep us updated.

  • DAL ON THE VAL says:

    what are the chances of reformations or if it will linger in the caribbean?

    • Levi says:

      Small storms like Don usually don’t survive the Caribbean, and once they dissipate they rarely reform. It is unlikely to be a threat beyond the central Caribbean.

  • dean says:

    Thanks Levi!

  • Anonymous says:

    Thank you!

  • kendel says:

    where is the center of Don expected to pass

  • Lenny says:

    Great forecast as usual!
    Thanks Levi!

  • tj says:

    quite a few models take this to hurricane strength. What do u think?

  • tfdez says:

    Thank you so much for all your great work / keeping us all well informed!

  • Sunlinepr says:


  • Sam says:

    Hey Levi,

    I have a doubt about something: why is it essential for a tropical cyclone to have a CLOSED area of low pressure? I understand that when a low opens up it’s usually called a “trough” of low pressure. Correct me if I am wrong, but usually, when a tropical system low opens up, it starts devoiding thunderstorms in an organized manner?

    Thanks in advance.

    • Levi says:

      Hi Sam,

      The technical answer is that a cyclone of any type by definition has a closed circulation.

      Meteorologically, an Earth-relative closed circulation is different from an open trough mainly because of the convergence pattern. In a closed low, air close to the ocean surface is slowed by friction and converges inward toward the low center, drawing warm, moist air inwards and forcing it upward to produce thunderstorms. An open trough, on the other hand, has surface winds that do not converge toward a central point everywhere. Instead, they usually converge toward an elongated region along the trough axis. This doesn’t allow for thunderstorms to form in a concentrated region as easily as a closed low does, which is necessary for a tropical cyclone to form.

      Hope this answers your question.

      • Sam says:

        Hey Levi,

        This was a question I’ve wondered over the past years, now I have a better understanding of the nature of tropical cyclones.

        Thank you for taking the time to respond to my question. You’re a brilliant professional with a gift of explaining what can be complicated things to some of us who very little knowledge about tropical weather, in a way so simple that even a children can understand.

        Kudos and keep up the excellent work!


  • Anonymous says:

    Why don’t you cover hurricanes TS’s in the Pacific?

  • Anonymous says:

    Why don’t you cover Hurricanes and TS’s in the Pacific?

  • Navysurfer says:

    Thanks for all your hard work Levi,

    Cheers Pop’s

  • Robert says:

    Although tropical storms or conditions can be unpredictable….we ALL GOT EYES! Just look at the various modules and you can see whether a storm is going to intensify or get blown out! Nothing but dry air out there now, so there’s virtually NO chance of anything forming of any intensity, plus we’ve got serious wind shear factors to boot! No need for Levi to conjure up anything…because there’s NOTHING out there! Now the weather channel clowns would have you glued to there channel as soon as a dark rain cloud appears!

  • Dave H says:

    Hi Levi,

    Can you comment on the SAL prevailing over the atlantic? Is this typical for this time of year? Is it driven by the Bermuda high, Saharan wind storms, or some combination?

    • Levi says:

      It’s not unusual to have a strong Sahara air layer across the tropical Atlantic in July. They are usually pushed off Africa by tropical waves and across the Atlantic by strong trade winds when the Azores high is strong.

  • Angler says:

    Any comments on the weather comping off Senegal in the next couple days?

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