An unexpected event occurred a few days earlier, on Monday, August 31, in the eastern Atlantic Ocean.
As background, the article notes that Atlantic hurricanes observed in modern records had generally developed farther west or in the central part of the ocean. Atmospheric disturbances capable of contributing to Atlantic tropical cyclones first travel across Africa, where they gain heat energy, and then move westward over the Atlantic, gradually acquiring their essential fuel: water vapour from the warm ocean. [source] [source]
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| Fred Cape Verde |
Hurricane Fred over the Cape Verde Islands in the eastern Atlantic.
It normally takes several days after warm air leaves the African continent for the additional conditions required for a tropical cyclone to develop. Consequently, many Atlantic hurricanes reach maturity only after travelling a considerable distance across the ocean. Some later approach the Gulf of Mexico or the eastern coast of North America. [source]
On August 30, a warm atmospheric disturbance over central Africa began moving westward toward the Atlantic, suggesting that a new storm might develop over the central Atlantic during the following days. Instead, something unusual happened: almost immediately after reaching the ocean, and only about a day later, the disturbance took advantage of a short-lived combination of favourable conditions and intensified rapidly.
For what the source describes as the first time in more than 160 years of records, residents of the Cape Verde Islands in the eastern Atlantic were warned to prepare for an approaching hurricane. The storm was named Fred.
After crossing the islands, Fred weakened almost as rapidly as it had formed. The article attributes its decline to factors including the comparatively dry atmosphere, cooler waters farther into the central Atlantic, and unfavourable wind shear.
The influence of El Niño on seasonal tropical-cyclone activity in the Pacific and Atlantic oceans.
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El Niño
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During 2015, wind shear—winds changing speed and direction at different atmospheric levels—had already inhibited the formation or strengthening of many Atlantic tropical cyclones. The article describes this shear as a secondary consequence of the ongoing El Niño in the Pacific. El Niño can favour increased tropical-cyclone activity in parts of the Pacific while suppressing or reducing Atlantic hurricane activity.
Even against that background, Hurricane Fred's development in the far eastern Atlantic was a rare event that attracted considerable attention from atmospheric scientists. [source]