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Le nhc is monitoring no less than 6 weather systems over the Atlantic basin this evening. It is an extremely rare situation. The activity this season (in terms of the number of cyclones) is simply huge and superior to anything we've seen so far (including 2005). On the other hand, the energy accumulated until today is low and is located during these first 3 months (however very active) at a lower level than what Irma or Dorian could have generated on their own! In short, it's very active but, apart from Laura, not very powerful… let's hope that it continues despite the current traffic jam. If we take into account that we enter the last week before the peak of statistical activity, this traffic jam is finally quite logical.
Out of the 6 systems monitored, there are the last 2 named cyclones (Nana and Omar) which are now in great loss of power. Oscar is lost in the Atlantic and nana has hit Belize and Guatemala quite a bit and will now concern Mexico in a tropical depression.
Then there is an extra tropical disturbance NE of Omar which does not concern many people.
The bad news
Much of the complexity of the situation is due to two factors. On the one hand the continuous flow of active waves coming out of Africa which brings a significant level of convection around Cape Verde and on the other hand the fact that the directing currents are not very marked in the area which generates speeds of low displacement and sometimes a little different. This leads us straight to the bad news which is linked to the fact that the 2 identified disturbances risk being brought to approach very very closely. This is bad news in the sense that this kind of situation is almost unpredictable. Models have always had great difficulty in understanding and anticipating these interactions which can lead to totally opposite conclusions. And when we add to that slow travel speeds, visibility becomes almost zero. We have seen this in recent days with already 2 identical situations which have led to nhc to raise the risk to ultimately bring it down to zero. The disturbance over the Atlantic center, for example, has been followed for almost 8 days, during which time it has crossed just half of the ocean! This is also very rare.
This very dense activity zone in the eastern half of the zone, the risks of interactions and the erratic movements of disturbances therefore make the situation unpredictable, and this is always bad news!
The good news
For once I will not address the issue of favorable environmental conditions or not for strengthening. For a simple reason: given the slow movement speed of all this, they will have plenty of time to change before disturbances arrive between 50 and 60W .. if they do! No, this time we will rather talk about the trajectory.
The pressure situation in the Atlantic is quite favorable to us. The anticyclone is currently located very north over the Atlantic, on 45 / 50N, ie off Saint-Pierre and Miquelon. A fairly weak high pressure ridge extends to the Bahamas.
This situation is favorable to the West Indies because the pressure on the major development zone is quite low (less than 1014 hPa) with an isobar of 1016 hpa along 25N. This configuration normally allows cyclonic systems which are reinforcing to move up quickly to the north and therefore avoid the West Indies.
And the good news is that the 2 major global models (GFS et ECMWF extension) predict that this situation should last for at least 5-6 days. We can therefore hope that the disturbances over the eastern ocean follow a slightly NW trajectory which prevents them from touching the West Indies. This is moreover what almost all global models anticipate today.
Conclusion
The situation could (I say “could”) be less worse for the West Indies than what the map of the nhc lets suppose. On the one hand, it is obvious that the risks of strengthening are real for the next few days, but the overall situation in the Atlantic may allow trajectories north of the arc.
This should not be taken lightly, however. We are entering the statistically most active fortnight of the season and the waves will leave Africa one behind the other. And on this volume, it is possible that some will be classified as a cyclone in the coming days. And beyond 5/6 days, the global forecasts losing a lot of their relevance, the possibility that the situation will change in terms of trajectory cannot be ruled out.
We are only halfway through the season and it is the half that generally sees the fewest powerful systems in the pool, so caution is in order… but without sinking into paranoia either, even if the cards are anxious. !
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Image credits; Tropical tidbits, NHC / Noaa, UW-CIMSS
