Rare late-season Eastern Pacific hurricane forms

Tropical Storm Kenneth formed over the weekend in the Eastern Pacific, and intensified into a hurricane late this morning. We are well past the date for the usual formation of the season's last storm, since the African waves spawned by the African monsoon, which serve as low pressure "seeds" to get the atmosphere spinning and trigger formation of more than half of the Eastern Pacific's storms, are rare this time of year. Kenneth formed from some unusual wave-like motions in the atmosphere over the Eastern Pacific that were not associated with African tropical waves. Since 1949, here have been just three Eastern Pacific named storms that formed after November 18. These three storms were an unnamed tropical storm on November 27, 1951; Tropical Storm Sharon on November 27, 1971; and Hurricane Winnie on December 5, 1983. None of these storms hit land, though the 1951 storm grazed the Baja. If Kenneth grows stronger than a 90 mph hurricane, it will surpass Hurricane Winnie of 1983 as the strongest Eastern Pacific storm so late in the season. Kenneth is moving westwards out to sea, and should not be a threat to land.


Figure 1. Morning satellite image of Tropical Storm Kenneth taken at 7 am EST November 21, 2011. Image credit: NASA/GSFC.

Atlantic's Invest 99L could become Subtropical Storm Tammy
In the Atlantic, Invest 99L, an extratropical storm in the middle Atlantic that is generating tropical storm-force winds, has the potential to transition into a subtropical storm over the next day or two. The storm currently lacks a well-defined surface circulation. If it develops one, 99L would be called Subtropical Storm Tammy. The storm is over waters of 26°C, and these waters will cool to 24°C by Tuesday, as 99L moves northeastwards out to sea. These water temperatures are near the limit of where a subtropical or tropical storm can form. The storm is not a threat to any land areas.

Jeff Masters