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Aletta's formation in Eastern Pacific ends Earth's 41-day tropical cyclone drought

By: Dr. Jeff Masters, 1:07 PM GMT on May 15, 2012

The first Eastern Pacific tropical storm of the 2012 hurricane season is Tropical Storm Aletta, located about 650 mi south-southwest of Manzanillo Mexico. Aletta was named at 03 UTC May 15, right at the official May 15 beginning of the Eastern Pacific hurricane season. The storm is headed west-northwest away from Mexico, and will not trouble any land areas. It is unusual to get a tropical storm forming this early in the year in the Eastern Pacific; since record keeping began in 1949, there have only been two that have formed by May 15--Hurricane Alma of 1990, and an unnamed 1996 storm. Aletta will not live for long--the storm is headed towards a region with high wind shear and cooler waters that should be able to destroy it late this week.

Figure 1. Morning satellite photo of Tropical Storm Aletta.

Earth's longest tropical storm-free period in at least 70 years
The formation of Aletta ends a 41-day streak without a tropical storm anywhere in the world. According to the UK Met Office, the 41-day period storm-less period is the longest span Earth has gone without a tropical storm in at least 70 years. The last time there were as many as 38 consecutive storm-less days was in 1944. Prior to Aletta, the last tropical storm on the planet was Tropical Storm Daphne in the South Pacific, which dissipated 06 UTC April 3, 2012. April is usually is the quietest month globally for tropical cyclones. The long storm-less period comes in the midst of a very quiet two-year period of global tropical cyclone activity. According to Dr. Ryan Maue, who specializes in tracking global tropical cyclone activity, 2010 and 2011 saw a total of 146 global tropical cyclones--the lowest two-year total since satellite observations began in 1970. The 24-month period April 2010 - March 2012 had 141 global tropical storms, which is also a record low. That's quite a turnaround from 2004 - 2005, which saw near-record high levels of global tropical cyclone activity.

The Atlantic is quiet
The disturbance near the Azores that developed on Saturday, Invest 92L, has weakened and is no longer being tracked by NHC. The models have backed off on their predictions of a potential subtropical storm developing over the Western Caribbean or waters near Florida this weekend, and none of the computer models is predicting tropical cyclone development in the Atlantic over the next seven days. If something did develop, the most likely location would be along an old frontal boundary between the Bahamas and Bermuda, early next week.

Jeff Masters


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