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  • Writer's pictureBryan Norcross

Carefully watching the Atlantic Tropical Disturbance as it slowly gets organized

The Tropical Disturbance in the far eastern Atlantic has a circulation, but it’s broad and the center is not well defined. Fairly soon, it is likely to pull itself together and become at least a tropical depression.

It will be named Tropical Storm Sam when its top winds reach 40 mph, which is likely to happen in the next few days.

The annoying thing about this system is its location in the tropical Atlantic. It is far enough south that it is unlikely to make a sharp turn to the north right away. It’s most likely to chug in the general direction of the Caribbean islands through next weekend.

The steering currents are pretty weak, so likely-Sam will move slower than many systems we watch. The presence of the remnants of Tropical Storms Odette, Peter, and Rose helps weaken the high pressure to the north, which is the driver of the forward motion. They might also cause a slight arc in the track toward the north, but that effect is uncertain. The big question is what happens in a week or so when likely-Sam reaches the vicinity of the eastern Caribbean islands.

Trying to project more than a week in advance is a total crap shoot. But the computer forecast models do tell us that a stronger Sam is more likely to turn north than a weaker version. So we’ll be rooting for Sam to strengthen as quickly as possible.

In the long term, a dramatic autumn dip in the jet stream is forecast to set up just off the East Coast of the U.S. in about a week. Some of the computer forecast models predict it will dip far enough south to deflect likely-Sam to the north when it gets near the Caribbean islands. Others say the effect of the dip will be something less.

The bottom line is, we can’t project more than 4 or 5 days in the future. There are too many variables. In addition, we know that computer forecast models are always suspect before a system has fully developed. Hopefully in 2 or 3 days we’ll have more consistent projections of how the weather pattern and likely-Sam will interact.

Elsewhere in the Atlantic, Peter and Rose are on the road to dissipation. Strong upper winds are affecting both of the systems, stripping the circulation centers of the thunderstorms they need to keep going.

To the north, the winter-type system that started life as Tropical Storm Odette is forecast to drop south toward warmish waters. The National Hurricane Center is giving the system a decent chance of once again becoming at least a quasi-tropical system. That’s not relevant to anything except that a stronger ex-Odette that is farther south is more likely to influence likely-Sam than a weaker version.

So it’s important to take this a few days at a time. On the internet you can see predictions that go out 15 days. But they are nonsense and misleading. We have to wait for likely-Sam to develop enough for the computer forecast models to understand the system and the surrounding atmosphere. Then we can pay a more attention to the predictions. And even then, beyond 7 days is hocus-pocus.

It’s way too early to be concerned. For now, we wait and watch. This drama is going to play out over 10 days to two weeks.


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