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July 2013
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Tropical Storm Chantal Threatens Lesser Antilles, Hispaniola, then Bahamas & SE US

   Posted by Levi at 2:34am on July 9, 2013

Invest 95L formed a closed circulation last night and was upgraded to Tropical Storm Chantal. Some slight strengthening has occurred today with thunderstorms persisting near and southeast of the center, which has been intermittently exposed. The reconnaissance aircraft mission this afternoon found flight-level winds in the NE quadrant supportive of 50mph surface winds. However, surface pressures were found to be 1010-1011mb near the center of circulation, with only weak and variable winds in the SW quadrant. This indicates that Chantal is still somewhat disorganized and weak, despite good convective organization on satellite imagery. This is likely due to the rapid trade wind flow in which Chantal is embedded, which makes it difficult to maintain a coherent circulation. While only weakly organized, Chantal is capable of producing the 50mph winds measured by the recon plane due to an already strong pressure gradient on the northern side of the storm due to a strong subtropical ridge to the north.

Chantal’s WNW motion is expected to continue for the next 48 hours as she tracks along the southern periphery of the subtropical ridge. In about 48 hours, all of the models agree that Chantal will likely pass over at least a portion of Hispaniola. Flooding will be a concern for Haiti and the Dominican Republic as a result. By this time, an upper low currently over the Bahamas will be in the vicinity of southern Florida, weakening the western edge of the subtropical ridge and allow Chantal to turn more towards the northwest into the Bahamas, with a reduction in forward speed. In 72-96 hours, a longwave trough will dig into the eastern U.S. and help turn Chantal more towards the north, possibly clearing the Bahamas. In 96-120 hours, all of the models agree that a trough-split will occur, with the base of the longwave trough splitting away over the north gulf coast, allowing ridging to build back in to the northeast of Chantal. This is likely to force the storm back towards the southeastern U.S. coastline near the end of the forecast period. Exactly where this turn occurs will largely depend on the timing of the arrival of both the longwave trough and Chantal herself, and uncertainty is large at this time frame. However, a turn towards the SE US appears likely.

While upper-level winds and warm ocean temperatures support intensification of Chantal, history has shown that storms with high central pressures approaching the lesser Antilles typically continue to struggle after crossing into the Caribbean. Thus, only limited intensification is expected, and the forecast peaks Chantal at 55-60mph before hitting Hispaniola, not quite as strong as the 70mph peak currently forecasted by the NHC. The models all agree that Chantal will have significant interaction with Hispaniola in about 48 hours, which should greatly weaken the system. Thereafter, wind shear may increase due to an upper trough near the northern Bahamas, which may hinder restrengthening of Chantal in the Bahamas. However, as the trough-split occurs over the SE US, the resulting upper low over the north gulf coast will begin backing westward away from Chantal, placing the storm in a region of light upper winds in between the aforementioned upper low to the west and another one to the east. This would be a favorable outflow pattern, and Chantal is expected to restrengthen during this time as it makes a turn towards the SE US coast. Exactly how much strengthening occurs is an uncertain question, as this is still about 5 days away, and the setup then may not be exactly as it is forecasted to be now. Regardless, the Bahamas and SE US should closely monitor Chantal’s progress. Hispaniola should also keep a close eye on Chantal, as serious flooding could result from heavy rains as her circulation passes over the island in about 48 hours.


15 comments

   

Comments

  • EagleHarbotZig says:

    Great Report Levi. Let’s hope that there is not a lot of development before Chantal slams into the US.

  • Kim says:

    Good morning Levi, what is your take this morning July 9th?the models have changed. Do you think this might end up in the gulf? It is takeing a seminar path to Ivan in 2004. Just a little concern over here in Pensacola. Thanks Levi! Kim

    • Levi says:

      The models have not changed much. Only slight shifts are occurring. The consensus is still that Chantal will end up in the Bahamas in 3-4 days. I still expect a bend towards the SE US after that, but exactly where landfall occurs is still an open question that will depend on exactly where and when Chantal reforms after crossing the mountains of Hispaniola. Just keep an eye on things. There are still several days until Florida may be threatened.

    • Jeff says:

      Pensacola wont get hit at all.

  • Brandon says:

    Thanks Levi!

  • Neven says:

    Hi Levi, I really like your vids. In fact, they’ve inspired me to do something similar for my Arctic Sea Ice blog updates (latest one here). I’m keeping it really simple now, using CamStudio and then converting the video to 480p to make it smaller, just trying things out.

    Do you have any tips you could give me on how to make vids as great as yours? I hope one day I can pack as much info in 1 minute as you do. Great stuff.

    • Neven says:

      Levi, I hope I didn’t say something wrong. I just meant technical tips, wrt settings etc.

      • Levi says:

        Oh no. I’m sorry, I must have missed your question.

        Thanks for the compliment. I would just say try to be as succinct as possible. I still struggle with that sometimes. If fewer words can be used to convey the same message, strive for that. That sinks in with people more, and they remember it longer and understand it better. Besides that it’s practice, practice, practice! It has taken me years to get comfortable recording these videos and make them sound natural.

  • Deb says:

    Good morning, appreciate your info and your time!

  • ariel says:

    hello. by thursday what do you think the effect will be in puerto rico?

    • Levi says:

      By Thursday, Chantal will be long gone from PR. Right now it appears PR will get clipped by Chantal’s northern side tonight and tomorrow.

  • Harry Cane says:

    Levi, What are your thoughts about an approach to SE Florida. I am in the Hollywood/ Ft Lauderdale Area. Seems to me that maybe a little squally weather and the worst will stay off shore. Seems like this area historically has had few direct hits with big storms. I have lived here since 1967 and have seen alot of close calls and a few side swipes (ie Andrew/Wilma/David) but seems like they either go south (Miami) or north Palm Beach).

  • Harry Cane says:

    Thank You Levi, You explain the patterns better than any other outlet that I know. Most others gloss over the facts leaving you with many questions. Keep up the great work Levi!!

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