Buzz
A hurricane formed in the Atlantic Ocean, which is typically expected during summer months. However, this event occurred in mid-January, deep into winter. By Friday morning, Alex had weakened to a tropical storm as it approached the Azores near Portugal. While unusual occurrences are not unheard of, this event stands out as particularly rare. What caused Hurricane Alex to form during such an unconventional time of year? The perfect alignment of atmospheric conditions, akin to nature hitting the jackpot, made it possible.
(Forecast trajectory for Hurricane Alex on January 14, 2016, as predicted by the National Hurricane Center. | Source: Dennis Mersereau)
According to the National Hurricane Center (NHC), the U.S. National Weather Service's tropical forecasting division, Hurricane Alex reached sustained winds of 85 MPH on the afternoon of January 14, 2016, with a central pressure of 981 millibars. Compared to the standard sea level pressure of 1013 millibars, this reading is notably low for a Category 1 hurricane.
The system that eventually became Alex existed for an extended period before intensifying into a hurricane several hundred miles northwest of Africa's coastline. The National Hurricane Center (NHC) initially predicted its development on January 7, when it was still an extratropical cyclone near Bermuda. They monitored its journey across the ocean as it transitioned into a subtropical storm and, unexpectedly, a hurricane seven days later.
Although forecasters were well aware of the storm's progression, its occurrence remains remarkable because hurricanes are not typically expected in the Atlantic during the winter months.
HURRICANE SEASON
(Climatological data on tropical cyclones in the Atlantic Ocean. | Source: NHC)
The Atlantic hurricane season officially spans from June 1 to November 30, with the peak activity occurring around September 10. As autumn progresses and cold fronts move across the United States, cooler air spreads over the Atlantic, causing tropical activity to decline sharply and making it increasingly difficult for new storms to form.
The concept of a 'hurricane season' is essentially a human invention—a timeframe on our calendar that marks when tropical systems are most likely to develop in a specific ocean basin. However, nature doesn't always adhere to our rules or fit neatly into our constructed categories. This is why events like the formation of Hurricane Alex on January 14 leave us both amazed and perplexed.
Tropical storms or hurricanes have been recorded in the Atlantic during every month of the year, though they are rarest in February and April, with only one occurrence each. January has also seen a few systems, including two notable storms that originated on December 30 of the preceding year. Tropical Storm Zeta, the final storm of the record-breaking 2005 Atlantic hurricane season, formed just before New Year’s Eve and lasted until January 7, 2006. Alex is only the third hurricane known to exist in the Atlantic during January, joining 1954’s Hurricane Alice (which formed on December 30 and persisted into early 1955) and an unnamed hurricane in early January 1938.
EXTRATROPICAL VS. SUBTROPICAL VS. TROPICAL
Visible satellite imagery of Hurricane Alex captured on January 13 and 14, 2016. Image credit: NOAA
In meteorology, there are three primary types of large-scale cyclones (low-pressure systems). The most common is the extratropical cyclone, characterized by cold and warm fronts circulating around its center. Often referred to as 'mid-latitude cyclones,' these systems derive their energy from the jet stream, which generates strong atmospheric lift over a broad area, reducing surface air pressure. Much of the dynamic weather we experience stems from extratropical cyclones.
In contrast, a tropical cyclone is entirely warm and moist throughout its structure. These warm-core systems derive their energy from the intense thunderstorms surrounding the eye, known as the eyewall, which thrive on the heat from the ocean below. Rapidly rising air within the eyewall creates extremely low surface pressure. However, the storm weakens quickly if dry air, strong winds, or cooler waters disrupt the eyewall thunderstorms.
A subtropical storm represents a hybrid between the other two cyclone types. It lacks cold or warm fronts and features a warm core while retaining some cold air in the upper atmosphere. Under favorable conditions, most subtropical storms in the Atlantic evolve into fully tropical systems, as Alex did. For those in its path, the distinction between subtropical and tropical is minimal, primarily relevant to meteorologists and weather enthusiasts.
WHY DID ALEX FORM?
(Sea surface temperatures in °C on January 13, 2016. | Source: NOAA/ESRL/PSD)
For a disturbance over water to develop into a tropical cyclone, three key elements are required: warm water, low wind shear, and sufficient moisture. In this instance, the eastern Atlantic Ocean experienced minimal wind shear, and the system that became Alex absorbed ample tropical moisture from the south, shielding it from dry air to the north and west.
The final factor was warm water, which is scarce in the northeastern Atlantic Ocean even during summer, and especially in January. While water temperatures were far below the usual threshold needed to sustain a hurricane, a unique condition arose. A significant temperature contrast between surface air and upper atmospheric air created strong instability, enabling rapid upward air movement. According to the NHC, the air high above the hurricane reached -60°C, an exceptionally cold reading. This steep vertical temperature gradient compensated for the lack of warm water, allowing thunderstorms to thrive and enabling Alex to defy expectations by becoming a hurricane.
Does this storm indicate anything about the upcoming summer hurricane season? Very little. The current El Niño in the eastern Pacific is expected to diminish by summer, potentially leading to a more active hurricane season than in 2015. However, Hurricane Alex is not a harbinger of future storms. This rare event was an anomaly, unlikely to recur for many years.
