Of course we’re referring to Hurricane Alex here, which blew up in far eastern Atlantic waters thought to be way too cold to spin up such a storm. Textbook meteorology says hurricanes, which feed off the heat of the ocean, won’t form over waters cooler than about 80°F. On the morning of January 14, Alex exploded over waters that were a chilly 68°.
Alex is (at least) the third hurricane observed in January, with others in 1938 and 1955. The latter one, Hurricane Alice2, was actually alive on New Year’s Day.
The generation of Alex was very complex. First, a garden-variety low pressure system formed over the Bahamas late last week and slowly drifted eastward. It was derived from the complicated, but well-understood processes associated with the jet stream and a cold front, and that certainly had nothing to do with global warming.
The further south cold fronts go into the tropical Atlantic, the more likely that they will just dissipate, and that’s what happened last week, too. Normally the associated low-pressure would also wash away. But after it initially formed near the Bahamas and drifted eastward, it was in a region where sea-surface temperatures (SSTs) are running about 3°F above the long-term average consistent with a warmer world. This may have been just enough to fuel the persistent remnant cluster of thunderstorms that meandered in the direction of Spain.
Over time, the National Hurricane Center named this collection “Alex” as a “subtropical” cyclone, which is what we call a tropical low pressure system that doesn’t have the characteristic warm core of a hurricane.
(Trivia note: the vast majority of cyclones in temperate latitudes have a cold core at their center. Hurricanes have a warm core. There was once a move to call the subtropical hybrids “himicanes” (we vote for that!), then “neutercanes” (not bad, either) but the community simply adopted the name “subtropical.”)
In the early hours of January 14, thanks to a cold low pressure system propagating through the upper atmosphere, temperatures plummeted above the storm to a rather astounding -76°F. So even though the SSTs were a mere 68°, far to cold to promote a hurricane, the difference between there and high altitudes was a phenomenal 144°, was so large that one could form.
Vertical motion, which is what causes the big storm clouds that form the core of a hurricane, is greatest when the change in temperature between the surface that the upper atmosphere is largest, and that 144° differential exploded the storms that were in subtropical Alex, quickly creating a warm core and a hurricane eyewall.
A far-south invasion of such cold air over the Atlantic subtropics is less likely in a warmer world, as the pole-to-equator temperature contrast lessens. Everything else being equal, that would tend to confine such an event to higher latitudes.
So, yes, warmer surface temperatures may have kept the progenitor storms of Alex alive, but warmer temperatures would have made the necessary outbreak of extremely cold air over the storm less likely.
Consequently, it’s really not right to blame global warming for Hurricane Alex, though it may have contributed to subtropical storm Alex.