On Saturday 22 September 2012 at 10:49 a.m. EDT (14:49 UTC) the Sun crossed the celestial equator marking the autumnal equinox, and the arrival of fall in the northern hemisphere and spring in the southern hemisphere.
Equinox from the Latin: equi (from aequus) = equal, and nox = night, is a term that identifies an astronomical event, which occurs twice every year, when day and night are technically equal lasting 12 hours. I say ‘technically equal’ because in theory it is true, but in practice there are some small details that result in a bit more than 12 hours of daylight, if we count the time from when we first see the top edge of the Sun emerging over the eastern horizon until we see the last of the Sun disappear below the western horizon.
The equinoxes are events that carry important significance for people around the world, especially those who have a historical tradition of studying the movement of the Sun in the sky throughout the year. The Maya in Mexico and Central America had an important and long tradition of astronomical studies, which is reflected in several monuments and buildings that they built throughout the region, which still exist today. On the day of the equinox you can see, even today, the Sun playing with openings or markings on these buildings in a display of scientific accuracy in the studies carried out by the Maya more than 10 centuries ago. It is truly amazing what they accomplished by using the power of observation and the computing ability of the human brain. A few years back I witnessed once such display during the vernal (spring) equinox when I visited the archaeological site of Tulum in Mexico.
To greet the arrival of fall in the northern hemisphere the tropics put up quite a display of tropical cyclone activity with four named storms, one in the Atlantic and three in the Pacific, actively in progress. In the northwestern Pacific, in a hot spot for cyclogenesis that has been particularly active in 2012 there was Typhoon JELAWAT and Tropical depression #19 both hovering over the Philippine Sea and moving toward the Korean Peninsula and Southern Japan. As I write this on 24 September 2012 JELAWAT is now a category 5 super-typhoon, and tropical depression #19 has strengthened to tropical storm strength, and named EWINIAR.
At the eastern extreme of the northern Pacific, in another hot spot for cyclogenesis off the coasts of Central America and southern Mexico, category 2 Hurricane MIRIAN was active to witness the crossing of our Sun over the equator. Today 24 September 2012 Hurricane MIRIAN was located some 500 km WSW of Puerto Vallarta, Mexico moving generally toward the NNW and forecast to make a turn toward the North and then northeast toward the Baja California peninsula.
Over in the Atlantic the 14th named storm of the 2012 Atlantic hurricane season, now Tropical storm NADINE was still active to the west of the Canary Islands more than three weeks since it emerged, as a tropical wave, near the Cape Verde Islands off the western coast of equatorial Africa. What is interesting about NADINE beyond its longevity, is the track it has followed since it became a tropical cyclone on 10 September.
With the autumnal equinox event and the arrival of fall in the northern hemisphere, we have seen 63% of the 2012 Atlantic hurricane season already go by including most of what is historically referred to as the peak of the season! What will Nature bring to the Atlantic in terms of tropical cyclone activity, in the just over two months that are left in the official 2012 Atlantic Hurricane Season?
Despite this show of tropical cyclone activity that greeted the autumnal equinox event and the change in seasons, the 2012 northern hemisphere season remains sub-par in terms of the number of named storms that have taken place compared with the historical average of the past fifty years. It will be interesting to see what the total number of tropical cyclones in the northern hemisphere will come to by the end of the year, but at least for now it would appear we might be in for a continuation of the pattern of reduced activity of the last two years.
Relative to this, what is important is to keep in mind that all it takes is one hit by a tropical storm, of any category for that matter, to cause damage and human suffering in the impacted communities. So it doesn’t really matter how many named storms there are in a given year, what counts us how many of those actually interact with the human environment.
In this regard our work is never fully done, for we must continue to pay attention, be prepared and above all practice mitigation!
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