Aug 05

Latest & Thoughts On Invest 90L In The Caribbean And Invest 99L In The Atlantic

To start the month, we are seeing an upswing in Atlantic tropical activity. Climatologically, this upswing is falling into perfect alignment with the peak of the Atlantic Hurricane season which spans, historically, across August and September. Looking at the latest NHC discussions, we note two areas of interest: (1) a wave in the southern Caribbean (Invest 90L) and (2) a wave in the Atlantic Basin (Invest 99L). Both waves have a decent chance at development through the week ahead.

WHAT WE KNOW: As noted, both areas of interest have a decent chance of development, in the short-term. There is greater confidence in Invest 90L having some type of impact on the Yucatan Peninsula and then into the Bay of Campeche over the next several days. Below are model plots for Invest 90L.

WHAT WE ARE STILL LEARNING: With Invest 99L in the Atlantic Basin, as noted, development is likely for at the least the near term. Up until the Lesser Antilles (set of islands that begin the Caribbean Islands), model plots are in fairly solid agreement on taking Invest 99L toward the Caribbean Islands. After this, things become uncertain, and for a number of reasons. For a few days, model output has taken Invest 99L north of the islands, and while a few still do, recent trends have suggested a slight shift south with the plots, overall. Below are model plots for Invest 99L.

UNCERTAINTIES: The first item that would lead to uncertainty, at the moment, with the future of Invest 99L is wind shear. An increased and elongated corridor of shear is situated directly in the forecast path of Invest 99L. Such conditions are unfavorable for long-term development as wind shear would tear the system apart. The second item is the topography of the Caribbean Islands. The islands feature rough terrain as mountains dominate the chain of islands. If the system manages to survive the shear, the terrain of the islands would almost certainly be its ultimate demise. The third item is the magnitude and extent of the SAL (Saharan Air Layer). This is dry air coming off the west coast of Africa that inhibits storm development across the Atlantic Basin. The SAL can extend as far west as the Caribbean Islands and a reason we saw minimal activity up until now. Shown below is a representation of shear tendency over the last 24 hours. Reds and Yellows indicate current shear. Note the elongated pocket of shear in the path of Invest 99L, some 40 to 50 knots.

Shown below is the current SAL coming off the west coast of Africa. When at its greatest, SAL produces dry air that inhibits tropical development in the Main Development Region.


FUTURE OF INVEST 99L: It’s honestly hard to say with great certainty right now. Some of the biggest questions that are naturally surfacing are whether this will survive future conditions and whether it can make it into the Gulf or up the US Eastern seaboard. That’s a tough call, and one that should not be made right now. Any Invest 99L forecasts out there right now that are calling for a Gulf or East Coast storm are just purely irresponsible. There are a lot of questions with this area of interest that need time and more data in order to be answered:

  • Can Invest 99L survive the shear in place?
  • Will shear dissipate ahead of the system dissipate?
  • If shear dissipates and Invest 99L strengthens, will it strengthen to fast and recurve out to sea or head up the East coast?
  • Will the SAL impact the development of Invest 99L

These are all questions that are surfacing, and ones we just don’t have the answer to at the moment, but in the days ahead, we should begin getting a better understanding of Invest 99L as the system becomes more organized.

PREPAREDNESS IS CRITICAL: No matter what the case, if you live anywhere from the southeast Texas coast to coastal Maine, be prepared during hurricane season. Pay close attention to the forecasts and have a safety plan in place.




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