Despite Quiet in the Atlantic, Signs Indicate Hyperactivity is Coming

What is causing the lull in tropical activity?

Namely, the Madden-Julian Oscillation (MJO). A lesser known phenomenon, the MJO is an eastward moving feature that traverses the planet through the tropics, returning to its starting point on a 30-60 day cycle, which means there can be multiple MJOs per season. The orientation of the MJO over the tropics dictates which areas will have the best conditions for tropical cyclone formation. Currently, the MJO has slipped into the west Pacific, leading to a higher wind shear phase for the Atlantic and East Pacific Basins.

Fortunately for us, wind shear is a hurricane dampener. Tropical storms need upper-level winds to blow from approximately the same direction and at the same speed in order to develop and strengthen. As wind shear by definition is variations in wind speed and direction, it can disrupt the delicate balance a hurricane needs to form. Tropical development may still be possible, though typically the systems end up both weaker and smaller due to the increase in sinking air and elevated shear speed—not necessarily directional—over the Atlantic Basin.

Accordingly, we expect the Atlantic Basin to be generally quiet through August 5-12. Any disturbances that might form would have a very low probability of developing due to wind shear.

What causes the forecast to shift from quiet to hyper-active?

The MJO is transient, however, meaning this lull will only be temporary. Current data indicate that the MJO will shift back across Africa, then possibly into the Indian Ocean, during the 3rd week of August and beyond. Should this happen, there is a strong possibility that we will see an uptick in the number of developing tropical systems, as well as an increase in intensity and striking power.

August and September are already considered the peak of hurricane season activity. With the shift in MJO, along with the current favorability of other long-range signals, we’re becoming more confident that we will see a very active pattern during this time period.

Starting August 13-20, tropical activity will begin to increase over the East Pacific Basin. Aug 21 through the end of September has a strong chance to be hyper-active, with several large-scale hurricanes likely to develop, leading to an elevated threat to Mexico, the Caribbean, and the United States.

With the ninth of the season, Hurricane Isaias, behind us and this upcoming period of hyper-activity, StormGeo has increased the forecast for named storms to 24.

Enjoy this respite from tropical activity, but also take the time to review your hurricane plans and make any last minute preparations. Our active season has only just begun.