Late season Atlantic tropical storms

There is currently no tropical activity of note in the Atlantic, nor do the models predict there will be any over the next six days. Wind shear over most of the tropical Atlantic is high and is expected to remain so for at least the next two weeks, which is typical for November in an El Nino year. However, we have to watch the Western Caribbean later this week, as the NOGAPS model predicts that wind shear may drop enough to support a tropical disturbance that could bring heavy rains to the region.

What are the odds of getting a tropical storm between now and April in the Atlantic? Well, if the past is any indication (Figure 1), we should expect no further activity in the Atlantic. Since 1950, when El Nino conditions have existed in the November-January period, as defined by NOAA's Climate Prediction Center, only 37% of those years have seen a late season tropical storm. There have been an average of 2.9 days per year when a named storm has been present in the Atlantic during those years. In La Nina years, late season tropical storm activity is 60% higher--about 5 named storm days per year. This year, we are experiencing a moderate El Nino (SSTs at least 1 degree above normal in the Equatorial region off the Pacific coast of South America). Late season Atlantic tropical storms have occurred in only 3 of 11 (27%) years with a moderate or strong El Nino.


Figure 1. Number of days per year that a named storm was present in the Atlantic during November-April. Years marked with a red "E" were El Nino years. Note that it is common to have zero late season tropical storms during El Nino years. It is interesting to note that there appears to be an increase in late season storms in the Atlantic in recent years. However, as I've discussed in a previous blog, this increase has not been seen in the Pacific Ocean.

My next update will be Wednesday, unless there's new tropical activity to talk about.

Jeff Masters