Category Archives: Tropical Cyclones

Are Tropical Cyclones around the Corner?

15 May 2011 marked the official start of the 2011 Hurricane Season in the eastern Pacific basin, and in less than two weeks on 1 June 2011 we will officially inaugurate the 2011 hurricane season in the Atlantic basin.

As we keep an eye on the tropics for any signs of potential tropical cyclone development along hurricane alley, the Caribbean, the Gulf of Mexico and the west-central Atlantic, as well as the eastern east Pacific, we note tropical waves on the move from equatorial Africa toward the west and areas of disturbed weather, which may eventually become threats to communities through the larger basin. Geostationary (GOES) satellites provide frequently updated imagery 24 hours a day year round, such as the one shown above [courtesy of NASA] where a large region of disturbed weather is clearly seen to the north of the U.S. Virgin Islands moving westward toward the USA mainland, which will collide with a front pushed by the jet stream toward the northeast by north. This image also shows quite a bit of tropical activity further south near the equator.

A color-enhanced infrared GOES satellite image, shown below [courtesy of NASA], also taken on 18 May 2011 shows the cell of disturbed weather mentioned above in more detail.

 On the image above notice how the large cell of disturbed weather over the west-central Atlantic is moving generally westward toward a collision with a storm system near the USA Atlantic coastline, which is being pushed by the jet stream toward the east by northeast. From this image it may be deducted that in the absence of a jet stream coming so far south and pushing toward the east by northeast, the cell over the west-central Atlantic might very well continue moving toward USA land where it may cause copious rain and possibly coastal flooding over the next 36-48 hours.

Meanwhile over the far eastern Atlantic, to the south of the Cape Verde islands, we are more and more everyday seeing tropical waves generated by the assembly line that is active over equatorial Africa, which eventually feed into the hurricane alley that channels them toward the Caribbean and the western Atlantic. Some of these tropical waves are shown on the satellite image of 18 May 2011 shown below:

A better overall perspective of tropical activity over the eastern Pacific and Atlantic-wide basin, which may at some point have the ability to impact the USA as well as several other countries, can be gained by the full-disk satellite image of Earth’s western hemisphere on 18 May 2011 that is shown below:

On the satellite image above the yellow outline across the Earth’s disk identifies the belt of tropical weather that circles the planet, and which when this image was taken on 18 May 2011 was clearly positioned to the north of the equator where it may already be capable of affecting the trajectory of tropical waves, which may impact the USA and other interests in the Caribbean and Gulf.

The overall perspective of tropical cyclone risk can be complemented by the map of sea surface temperature from 17 May 2011, which shows hurricane alley, the Caribbean and Gulf as well as the eastern-east Pacific have already reached a thermocline that is favorable for cyclogenesis. This map of sea surface temperature is shown below:

The above sea surface temperature map [courtesy of NOAA] also shows the effect of the La Nina [ENSO] event still active off the coast of Peru, where the green and yellow color identify the much cooler waters of the La Nina event. The historical record has shown that a La Nina event creates an atmosphere-ocean environment that is more conducive toward tropical cyclone generation in the Atlantic basin.

Finally, I believe it is important to take a closer look at tropical activity over the eastern Pacific off the coasts of Central America and Mexico where a satellite image on 18 May 2011 shows several large cells of rain and storms and otherwise disturbed weather that are active in that region. This region of the Pacific has seen quite a bit of storm activity the same as the junction between Panama and northern South America (Colombia and Venezuela), which has resulted is repeated incidents of heavy rains and thnderstorms over most of the area over the past several weeks. This is a pattern that developed in 2010 driven by La Nina, which appears to be repeating in 2011. The satellite image that follows below, showing the eastern Pacific near Central America on 18 May 2011 illustrates the commentary made before:

With such widespread tropical activity, and so many of the triggers for tropical cyclone development already present in these basins, i.e.: warm and warming surface waters, tropical waves and areas of disturbed weather, areas of low atmospheric pressure etc., it is clear possible tropical cyclone development may occur at any time from now on, so it becomes imperative we remain prepared, pay attention and continue to practice mitigation!

The Northern Tropics in May 2011

Gradually with the onset of spring in the northern hemisphere  we have seen that tropical band just north of the equator get active with tropical waves, increased sea surface temperatures, rain, thunderstorms, and flaring areas of disturbed weather worldwide. 

Such tropical activity shows clearly within the belt of tropical activitygirddling Earth on the composite satellite view [courtesy of NASA] below:

Full disk composite satellite view of Earth's western hemisphere on 8 May 2011

 On the satellite image two areas are of especial interest to those of us in the United States: (a) One is the eastern-east Pacific just off and west of the coasts of Central America. This region, together with the junction of the isthmus of Panama with South America [Colombia] saw extraordinary rain an storm activity for a good portion of 2010, which was attributed to the effects of La Nina active off the coast of Peru, leading to a number of cyclonic events over Central America, Southern Mexico and the Gulf of Mexico and  above average rainfall over most of Central America, particularly Nicaragua, Costa Rica and Panama as well as portions of northern Colombia and Venezuela with several flooding events.  During the spring of 2011 La Nina is still active, although in a somewhat weaker mode than in 2010, and severe thunderstorms and rain have already affected that Panama – Colombia junction, raising the possibility that we might see more of the same during the summer and fall of 2010. The satellite image below [courtesy of NASA]:

of the Central American region on 8 May 2011″] (b) The other one is the eastern Atlantic, which marks the junction between mainland equatorial Africa and the so-called hurricane alley starting in the neighborhood of the Cape Verde Islands and then west by northwest toward the Antilles and the Caribbean. This area is the terminus for the tropical-wave assembly line that traverses equatorial Africa from east to west and serves as the transport for pulses of disturbed weather often originating over the Indian Ocean, which pick-up heat and moisture over equatorial Africa causing rain and thunderstorms. This activity generates tropical wavesthat emerge over the eastern Atlantic providing fuel fo potential tropical cyclone development. A satellite view of this region on 8 May 2011 already shows plenty of tropical wave activity giving way to cells of rain and thunderstorms south of the Cape Verde Islands moving west along ‘hurricane ‘alley’:

of the eastern Atlantic and western equatorial Africa region on 8 May 2011″]Completing the picture, also on 8 May 2011 a tropical low over the western Pacific became the first tropical cyclone of the the year in northern hemisphere. This is tropicl storm AERE moving toward landfall in the Philippines near the capital city of Manila. The forecast is for the storm to traverse the island and then make way toward Taiwan and possibly Japan under favprable ocean-atmospheric conditions. It would appear then that conditions for cyclogenesis are gradually congealing and becoming more favorable as spring rushes toward summer in Earth’s northern hemisphere. The satellite picture below shows the tropical cyclone on 8 May 2011 just east of the Philippines’ coastline:

showing tropical storm AERE on 8 May 2011 as it approached landfall in the Philippines.”]It is clear the northern tropics are being fueled by warming oceans and atmosphere as the Earth’s axis continues to tilt, bringing the northern hemisphere into full view of the Sun. Conditions are now in place that could soon generate tropical cyclone activity over the eastern Pacific and the eastern Atlantic; if we take into account the continued warming of surface waters in the Atlantic, Caribbean and Gulf, as well as in the eastern east Pacific plus the continuous presence of La Nina off the coast of Peru we may be looking at an active 2011 hurricane season in the Atlantic basin.  Relative to this the Colorado research duo of Bill Gray and Phil Klotzach recently presented their early forecast for the 2011 Atlantic hurricane season, calling for a total of 16 named-storms including 9 hurricanes, of which 5 may reach major hurricane strength (category 3 and above in the Saffir-Simpson scale of hurricane intensity).

Nature is sending us signals through this activity in key regions of the northern tropics. It behooves all of us in vulnerable coastal communities to pay attention to those signals, to be prepared and to practice mitigation to reduce the potential for damage from the impact of hurricanes, which will eventually come our way!