Even though we had tropical storms Alberto and Beryl already, they were both outside of the hurricane season. Since then, things have been nice and quiet. There are, however, indications that this may change. Let’s take a look at why.
There is an atmospheric phenomenon called the MJO or Madden-Jullian Oscillation that can sometimes lead to increased tropical cyclone formation when it is in its favorable mode. Think of it as a period of fertility in the tropics. A time when rising motion in the atmosphere is more prevalent, allowing deep tropical convection to form. This is what we call the “wet phase” of the MJO pulse and it typically adds a lot more showers and thunderstorms to the tropical regions of the globe where it circulates through.
On the other hand, the “dry phase” is easy to spot due to the sinking motion of the atmosphere, suppressing tropical convection. While development can take place during an MJO dry phase, it’s a lot more common to have development during the wet phase.
There are several computer models, the global models, that predict the MJO pulse and we can track that on various sites. The graphic I have linked to for this blog shows the operational GFS and its ensemble mean- the average of the various other runs of the GFS with slightly different variables. This model, along with others such as the reliable ECMWF, point to an increase in the wet phase of the MJO for the eastern Pacific and eventually the Atlantic Basin. When the MJO is within regions 8 and 1, we should begin to look for an increase in tropical convection. So, going by the graphic, we will need to pay closer attention to the tropics after about the mid part of the month as the wet phase moves through.
You’ll notice first, as it moves through the western Pacific, that we’ll see a typhoon or two develop followed by likely development in the southeast Pacific off the coast of Mexico and Central America. After that time, it is possible that a window of opportunity will open for the western Caribbean. It’s just another piece of the puzzle or a clue that we can use to know when the tropics are perhaps a little more ready for development than at other times. I’ll keep up with it and post more here as we get closer to the predicted date of the favorable MJO pulse.