Zeta May Be Forming In The Caribbean

The 2020 Atlantic hurricane season is still upon us. Hurricane Epsilon is heading off into the North Atlantic, but there is no rest for hurricane forecasters. The National Hurricane Center is now watching a new area of interest in the Caribbean Sea. If it develops into a tropical storm, it will be named Zeta. Would it be odd for this time of year? The answer is complicated.

Before I delve into the answer, let’s take a look at the current status of Invest #95L, the technical name given to the storm system of interest by NOAA. According to the National Hurricane Center Friday afternoon update, “Satellite images and radar data indicate that the broad area of low pressure located just west of Grand Cayman Island is gradually becoming better defined.” Forecasters give the storm a 70% chance of further development within the next 2 to 5 days. Whether it becomes Zeta or not, significant rainfall will be possible over the weekend in Cuba, Jamaica, southern Florida, and parts of the Bahamas. The ultimate path of the storm (towards Florida or further into the Gulf of Mexico) will depend on how it interacts with a cold front sweeping eastward in the United States. If you live in Florida or along the eastern Gulf of Mexico, watch the forecast carefully over the weekend.

Ok, let’s get to the question about “odd.” It is certainly not odd to have tropical cyclones at this time of year. The map below shows a climatology of tropical cyclone origin points in late October over the period 1851 to 2015. If Zeta forms, it is within a region of the Atlantic basin where we tend to see development. However, here is where things get a bit more complicated.

If Zeta forms, it will be only the second time in history that we have used the name Zeta. That is odd. As you recall, when the hurricane name list is exhausted, the Greek alphabet is used. The only other time this was employed was 2005. That year, Zeta, which is not the last letter in the Greek Alphabet, was reached. There is one major difference between 2005 and 2020. In 2005, Tropical Storm Zeta was named on December 30th and dissipated in January. According to a Tweet by Colorado State University hurricane expert Phil Klotzbach, “Current record for earliest 27th Atlantic named storm formation is November 29, 2005” He goes on to explain that the previous record was for the 2005 version of Epsilon but an additional October storm was added after the season in 2005. This oddity explains why the 27th named storm was Epsilon in 2005. The 27th named storm in 2020 will be Zeta (if it develops).

In a season of records for the 2020 Atlantic hurricane season, CIRES research scientist Sam Lillo points out another potential oddity. He tweeted, “Since 2000, there are 4 instances of two simultaneous tropical cyclones in the Atlantic after October 23rd.” That is not the punchline however, he went on to say, “There are zero instances between 1970 and 2000.”

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