Early 2013: Tropical Cyclone Activity in the Southern Hemisphere

Just a few days ago on 21 December 2012 the Earth’s axis reached its maximum tilt placing the ‘Tropic of Capricorn’ directly under the Sun, marking the onset of Winter in the Northern Hemisphere and Summer in the Southern Hemisphere.

With this event the oceans, which cover more than 80% of the Earth’s southern hemisphere, are receiving the maximum amount of Energy from the Sun continuing the warming trend started with the autumnal equinox in September of 2012. This natural annual cycle not only increases the sea surface temperatures, but it also increases the accumulated heat contents in the southern oceans and with it the potential for cyclogenesis in the ‘bottom’ half of our planet.

Today 2 January 2013 there are continuing signs that the southern tropics are indeed under the influence of factors that are usual contributors to cyclogenesis. Two tropical storms, tropical storm Freda in the South Pacific and tropical storm Dumile in the southern Indian Ocean, are currently active and threatening nearby islands. In addition there are two areas of low pressure and disturbed weather in the Indian Ocean and the South Pacific that are showing signs of strengthening and potential for cyclonic development, which warrant monitoring.

Color-enhanced infrared satellite image of the South Pacific on 2 January 2013 showing tropical storm FREDA over New Caledonia, and a cell of disturbed weather to its northeast, which may warrant further monitoring









Tropical storm Freda originated over the Coral Sea and earlier today was moving toward the southeast for possible landfall in New Caledonia with maximum sustained winds of 65 kph, gusting to 82-85 kph. While the storm is generating some heavy rains  around its center it appears to be weakening as it interacts with the island.

Color-enhanced infrared satellite image of the Indian Ocean on 2 January 2013 showing tropical storm DUMILE to the west of Madagascar, as it approaches the island of Reunion, and a separate cell of disturbed weather to its northeast that may develop further over the next day or so

Tropical storm Dumile was moving generally southward some 600 kilometers east of Madagascar on a course that threatens the island of Reunion in the southern Indian Ocean. The storm which is currently generating maximum sustained winds of 105 kph with gusts of up to 130 kph, appears to be strengthening and may reach hurricane strength within  the next 24-48 hours as it moves in a favorable environment.

Composite of satellite images creating a global mosaic over Australia, showing water moisture in the atmosphere to highlight the location of the tropical storms and cells of disturbed weather mentioned before

Elsewhere in the world conditions vary by region. Stormy conditions prevail over the northern latitudes across North America, Europe and Asia. A train of waves of disturbed weather continues to move eastward from the western Pacific region toward North America where their interaction with the jet streams has contributed to record snowfalls over vast portions of Canada and the United States.

Color-enhanced infrared satellite image showing the train of disturbed weather waves moving over the northern Pacific Ocean toward North America, where their interaction with jet streams has generated extreme stormy weather over large regions of Canada and the USA

In contrast with such prevailing conditions over the northern latitudes, most of the Atlantic Basin is under a regime of high pressure and dryer air with no storms present on this 2nd day of the new year.

Color-enhanced infrared satellite image showing the Atlantic basin north of the equator on 2 January 2013. Notice how clear and devoid of storms or disturbed weather cells the whole basis is on this day

While monitoring such current tropical activity pondering  what the rest of the year may bring in terms of tropical cyclone, it may be of interest to note that on a worldwide basis the year 2012 saw an increase in the total number of named storms after having shown a decline over the previous two years (2010 and 2011) to end just slightly below the average for the last fifty years or so. Based on this it could be said that we nearly had an average year in 2012 in terms of the total number of tropical cyclones on a worldwide basis.

Regarding the level of tropical cyclone activity in 2012 one significant change was a noticeable shift in the level of activity  toward the northern hemisphere. In 2012 we saw increases in the total number of named storms in the four basins for cyclogenesis in the northern hemisphere, from the total numbers generated in 2011. The eastern Pacific basin off the coast of Central America and Southern Mexico generated 17  tropical cyclones in 2012 versus only 11 in 2011, while the Northwestern Pacific basin saw a total of 25 tropical cyclones generated in 2012 versus 21 in 2011. The Atlantic basin increased from 18 named storms in 2011 to 19 in 2012, a slight increase  in total number of tropical cyclones, but perhaps the most noticeable change in this basin was the reduced level of intensity experienced as most of the cyclones generated did not reach hurricane strength, staying within tropical storm levels.

What do these numbers mean? What can we learn from the noticeable shift in tropical cyclone activity to the  northern hemisphere, where most of the world’s population lives?

One simple answer is that 79% of the total number of tropical cyclones generated worldwide in 2012 took place in the northern hemisphere, compared with an average of 69.3% in the past twelve years A(2001 through 2012) and only 62.2% in 2009, 66.7% in 2010 and 68.4% in 2011.  While these fluctuations may just be part of   the natural variability of cyclogenesis the reality is that the main drivers for this are not well understood.

Few or no conclusions can be drawn about the significance or this because of the extremely short time period being assessed, however  should this eventually develop into a trend toward more tropical cyclones in the northern hemisphere, even if most do not reach major hurricane intensity, residents in vulnerable communities in the USA and elsewhere would do well to start focusing much more intensely on preparedness and mitigation rather than on response. Relative to this it is critical for all to keep in mind that even a minor hurricane or a tropical storm are capable of inflicting considerable damage and human suffering, as it was so graphically demonstrated by the impact of Hurricane SANDY in 2012.

Be prepared! MITIGATE!


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