Coastal regions of the Indian Ocean are experiencing a terrible hurricane season.
Perhaps this hasn’t been clear if you’ve followed the news in recent days and weeks about two storms decimating different parts of the African nation of Mozambique and another slamming into India, because these storms have been referred to as “cyclones.”
And that is what they are called in that part of the world.
But, in fact, cyclones in the Indian Ocean, typhoons in the western Pacific Ocean and hurricanes in the Atlantic Ocean and eastern Pacific are all the same type of storm.
The differences in regional nomenclature often cloak the fact that these type of storms are brethren, fueled by the latent heat from the condensation of evaporating warm ocean water, developing a calm, clear “eye” at the center as they intensify, spun counterclockwise in the Northern Hemisphere and clockwise in the Southern Hemisphere by the Earth’s rotation.
Hurricanes by any name are a little more on our minds than is normal in early May because of Wednesday’s arrival of two “hurricane hunter” aircraft at the Roanoke-Blacksburg Regional Airport for the East Coast Hurricane Awareness Tour. Public tours are scheduled for 2 to 5 p.m.
South of the equator, summer has emerged into fall, and, similar to what happens in the Atlantic Ocean during the same seasonal shift in September and October, this has fueled the development of tropical systems in the western Indian Ocean east of Africa. Cyclone Idai in March and Cyclone Kenneth last month each made landfall in Mozambique.
Idai killed more than 1,000 people in four nations, including more than 600 in southern Mozambique. Kenneth is considered the strongest tropical cyclone on record in Mozambique, with sustained winds in excess of 130 mph as it came ashore in northern Mozambique, but a concerted effort to evacuate tens of thousands from vulnerable coastal areas appears to have kept the death toll well under 100.
Just north of the equator, the extremely warm waters of the Bay of Bengal can fuel strong tropical cyclones during a much wider timeframe than is typical in the North Atlantic and Gulf of Mexico. Cyclone Fani rolled into the northeastern India state of Odisha last week with maximum sustained winds of more than 150 mph. The death toll was also limited by a massive evacuation undertaken by local officials.
In meteorology, we have gotten a lot of mileage out of the term “cyclone,” though all refer to various versions of the same principle.
Any low-pressure system, with rising air spinning counterclockwise in the Northern Hemisphere or clockwise in the Southern Hemisphere, is, generically, a “cyclone.”
This usage, while common in meteorologists’ chatter among themselves, has been most prominent in the public eye with the recent ascendancy of the term “bomb cyclone,” referring to a rapidly deepening low-pressure system, often in spring and winter.
These kind of cyclones form along the boundaries of contrasting air masses with very strong winds aloft — opposite conditions than are optimum for tropical cyclones.
“Tropical cyclones” refer to a closed low-pressure system deriving energy from the latent heat as evaporating warm ocean water condenses, ranging from mere tropical depressions with winds under 39 mph to mighty Category 5 hurricanes and super typhoons with wind speed topping 156 mph.
In the Indian Ocean, as has been discussed, a capital-c cyclone followed by a name from a long list is used to identify a particular powerful tropical cyclone, what would be known as hurricane in the Atlantic basin.
Tornadoes were often referred to as “cyclones” in historic and news accounts from the 1800s and even into the early decades of 1900s. Most tornadoes are in fact “cyclones” in that they are intense, upward lifting and counterclockwise-rotating localized low-pressure systems. A small percentage, however, rotate in the opposite direction, and are therefore “anticyclonic” tornadoes.
The “cyclone” term for tornadoes has been almost totally abandoned in recent decades.
In truth, our weather is constantly affected by a complex interplay of cyclones and anticyclones at various levels of the atmosphere, the cyclones generally bringing clouds and moisture and the anticyclones generally bringing dry weather.
Anticyclone-dominated weather brought us a dry Monday to start the week, but the next cyclone is on its way with showers and storms for late week. Be thankful it’s not a capitalized cyclone with a name and that the hurricane hunter planes have time on their hands for public tours right now.
Weather Journal appears on Wednesdays.