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Two Caribbean disturbances head toward the tropical development zone

Oct. 1 satellite image of the tropics.
Oct. 1 satellite image of the tropics. (CIRA/RAMMB)

A broad area of low pressure is developing over Central America with influence extending over the western Caribbean, Mexico’s Yucatán peninsula, and into the adjacent waters of the Pacific. This typical autumn weather feature is called the Central American Gyre – gyre meaning a large rotating system.

Over the next week or so, two tropical disturbances will get ensnared in this large system’s circulation.

First comes Tropical Disturbance #1, which is on the eastern flank of the developing larger circulation. The disturbance is already showing signs of rotation, although its thunderstorms are quite disorganized.

Upper-level winds are tilting the system and keeping it from fully organizing immediately. Over the next couple of days, however, those hostile winds are forecast to let up. A bubble of atmospheric conditions supportive of development is forecast to cover the western Caribbean just as the disturbance arrives in that area, and is drawn under the influence of the Central American Gyre.

The National Hurricane Center is giving this disturbance a high chance of developing into a tropical depression or tropical storm in the next few days. If it is the next one to be named, it will be called Tropical Storm Gamma.

When the disturbance reaches the Caribbean waters off the coast of Mexico’s Yucatán Peninsula, the steering currents are forecast to weaken with the system left to meander near the Yucatán coast, rotating within the Gyre’s broad circulation. If it drifts over land, it will likely stay fairly weak. Or conversely, if it meanders for a longer time over the warm Caribbean or Gulf waters, it will have a better chance of gaining some strength.

People in Belize, the Mexican Yucatán, and western Cuba should stay aware since, as we’ve seen, slow-moving tropical systems are less likely to be predicted well.

The general consensus of the tropical forecast models is that Disturbance #1, or whatever it becomes, will rotate around or across the Yucatán into the Gulf ensnared by the broad flow around the Gyre. Nothing is likely to happen fast.

Then next week, Disturbance #2 will come along and a similar scenario may play out, with the disturbance, which may become a tropical depression or tropical storm as well, getting caught up in the Gyre’s broad rotation.

While all this is playing out, periodically, the northern jet stream is forecast to dip down into the Gulf of Mexico. When it does that, we have to watch to be sure the dip, which acts as something of a scoop, isn’t strong enough to pull one of the systems north toward Florida or the Gulf coast.  In general, the stronger the tropical systems become, the higher chance they can be grabbed and scooped to the north.

Right now, there are no signs that’s going to happen, but it’s not impossible.

In any case, the scooping jet streams will create corridors of tropical moisture that stream over Florida, and South Florida in particular. The heaviest rain with these corridors usually occurs when the moisture interacts with a front draped across the region.

Currently the front that pushed down the state over the last couple of days has parked over the extreme southern peninsula. Over the next few days it will likely meander north, which will keep South Florida in the moist tropical air. As a result, periods of heavy rain are expected through the weekend, and perhaps into next week.

The National Weather Service is predicting 4 to 6 inches of rain over the next few days, and this will be on top of extra-high tides, which make drainage systems in many coastal areas function poorly.

Be very aware of flooded streets after heavy downpours. The water is likely to clear much more slowly than normal.

So we’ll keep an eye on the tropics, but the other eye on the sky and on the potentially flooded road ahead.


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