Tag Archives: Wind shear

It looks like cyclonic activity out there!

The historical records, going back some more than 150 years, show tropical cyclones occurring in every month of the year both in the eastern Pacific and the Atlantic north of the equator. Despite this fact we have identified those months when tropical cyclone activity is more likely to take place to define what is known as the annual hurricane season. The eastern Pacific hurricane season will officially start this week on Tuesday 15 May 2012, while the Atlantic hurricane season must wait another couple of weeks to officially get started on 1 June 2012.

Although Mother Nature will be the  one deciding when to generate tropical cyclones in either of these two basins, there have been numerous recent signs that some of the factors that contribute to cyclogenesis have began to get stronger  and more organized, laying the foundation upon which a coincidence of favorable conditions could trigger a tropical cyclone at any time moving forward.

After being turned off for several months the tropical wave assembly line over Equatorial Africa is once again present generating waves of tropical activity that march to the west toward the eastern Atlantic and hurricane alley as shown in this color-enhanced infrared satellite image of 3 May 2012

Among those favorable signs we have recently seen the tropical wave assembly line over equatorial Africa become more prevalent to the north of the equator, while the belt of tropical activity to the north of the equator, which had been absent for several months, has started to once again show as a continuous region of rain and thunderstorms reaching from the eastern Atlantic all the way to the central Pacific and beyond. The tropical wave assembly line converts pulses of disturbed weather generated over the Indian Ocean into tropical waves consisting of regularly spaced cells of rain and thunderstorms that move west over Equatorial Africa to eventually emerge over the warm waters of the eastern Atlantic southward of the Cape Verde Islands, aiming for what is known as hurricane alley.

Composite satellite image of 3 May 2012 showing what is known as the 'belt of tropical activity' extending from the eastern Atlantic to the central Pacific ocean
A region of disturbed tropical weather marked by rains and thunderstorms over northern South America and the waters of the eastern Pacific Ocean off Central America are becoming prevalent as we approach the change of seasons

In addition to these early signs that hurricane seasons may not be that far off, other activity over the tropical regions of the northern western hemisphere mark the onset of other contributing factors, which include: (a) the development of a persistent region of disturbed weather, marked by rain cells and thunderstorms over the eastern Pacific Ocean to the west of Central America and South of Mexico, and (b) the continuing warming of surface waters over the tropical regions of the north Atlantic and north Pacific oceans.

Both of these indicate the heat content in the tropical oceans continues to increase, providing a source of energy for potential tropical cyclone generation in the future. On the other hand the persistent region of tropical activity over the eastern Pacific marks a sub-basin where cyclogenesis takes place.

Satellite-based map showing sea surface temperatures over portions of the Pacific and Atlantic oceans on 12 May 2012 that include a vast area of 30+ Celsius temperatures to the west of Central America

In case more signs were needed, today Sunday 13 May 2012 there are two new signals provided by Mother Nature, one in the Atlantic and one in the eastern Pacific, which tell us to pay attention and keep watching for potential further development.

Water vapor satellite image of the Atlantic on 13 May 2012 showing a distinct region of low pressure just south of the Azores Islands that warrants close attention
Color-enhanced infrared satellite image of 13 May 2012 showing the same potential cyclonic activity near the Azores Islands in the Atlantic

The weather system shown on the images above was located some 500 kilometers to the southwest of the Azores and moving toward the northeast. While the system is showing some cyclonic tendencies, it is tracking over a region of the Atlantic with cooler surface waters although the surrounding environment is one experiencing low wind shear, which might be conducive for some better organization and further development of this system. Both of these regional conditions are illustrated by the images below:

Satellite-based map of sea surface temperatures on 12 May 2012 showing the progressively cooler surface waters ahead of the weather system approaching the Azores
Wind-shear superimposed on a satellite image showing the Atlantic on 13 May 2012 and the area of low wind-shear around the weather system of interest near the Azores Islands

The other signal that has emerged in the early hours of Sunday 13 May 2012 is over the eastern Pacific Ocean some 500 kilometers southwest of Acapulco, Mexico and 1,500 kilometers west of Guatemala. The signal identifies a region of low pressure and disturbed weather moving over rather warm surface waters in a low wind-shear environment, which provide rather favorable conditions for further development  and potential strengthening over the next 12-24 hours. This is clearly a system to be watched, which is being monitored closely by NOAA’s National Hurricane Center.

Satellite image of 13 May 2012 showing water vapor in the atmosphere over the eastern Pacific Ocean near the coast of Mexico and Central America where an area with potential for cyclonic development is clearly visible
Color-enhanced infrared satellite image of 13 May 2012 showing the same region of the eastern Pacific Ocean seen in the image to the left

Elevated sea surface temperatures and low wind-shear conditions, which create a favorable environment for the system we are following over the eastern Pacific Ocean near the western coastline of Mexico, are illustrated by the satellite images below:

Satellite-based map of sea surface temperatures on 12 May 2012 showing a large region of waters at temperatures ranging from 28 to 32 Celsius near the coast of Mexico where we are monitoring a weather system with potential for cyclonic development
Satellite image of 13 May 2012 showing the eastern Pacific Ocean off Mexico and Central America and current wind-shear conditions over the area where we are monitoring a potentially cyclonic weather system\

This specific disturbed weather system over the eastern Pacific is moving approximately west by northwest, and it is being given a 50% probability for further development by the National Hurricane Center, which is monitoring it closely. Could this be the first tropical cyclone of the Eastern Pacific 2012 hurricane season, right on target or just a sampler of things to come? Only time will tell, keep watching, pay attention! Be prepared!! Mitigate!!!

Related to this, the 26th Annual Governor’s Hurricane Conference gets under way tomorrow Monday 14 May 2012 at the Fort Lauderdale Broward County Convention Center. While the conference will be officially inaugurated in the early afternoon on Wednesday 16 May 2012, a full program of training sessions starts on Monday morning. It will be interesting to see if Mother Nature will provide a relevant backdrop in terms of tropical cyclone activity.

Hurricane TOMAS: Uncertainty Ahead

GOES satellite view of category 2 Hurricane TOMAS in the eastern Caribbean on 31 October 2010 moving west by northwest

31 October 2010 – All hollows eve day – Hurricane TOMAS now a category 2 tropical cylone is showing signs of further strengthening as it begins to come under the influence of several factors that will affect its trajectory for the next several days: southwesterly wind shear, a front that has come down all the way to the southern Gulf and the Florida straights moving toward the east, and other atmospheric factors have caused Tomas’s track to shift northward and are expected to eventually cause it to start a turn toward the north while also slowing down its forward progress.

Projected track of Huricane Tomas on 31 October 2010 prepared by hte Navy Research Laboratory on the basis of NOAA observations and data

The projected net result is a hurricane that may come closer to the Antilles, must probably Hispaniola (Haiti), Jamaica and southeastern Cuba, but which may then veer once again toward the northwest perhaps toward the end of the week and at that point the Yucatan Peninsula, the Gulf and even Florida would all become potential targets, but the degree of uncertainty so far ahead is so large that any forecast would be quite speculative at this time.

GOES satellite view of hurricane Tomas, on 31 October 2010 at 0745 EST, showing waver vapor in the atmosphere, which helps visualize the atmosferic factors currently affecting the system's trajectory.

At present all interests in the Caribbean basin must monitor TOMAS’ progress carefully over the next few days and remain on alert for possible activation of emergency preparedness plans.

TOMAS: 1 November 2010

GOES satellite image of tropical cyclone TOMAS on 11 November 2010 at 0915 EST. Notice how the heavy rain is located far to the west of the center of circulation. In this view Tomas was located half-way between the southern coast of Puerto Rico and Caracas, Venezuela moving west by northwest.

Tropical cyclone TOMAS has weakened considerably over the past 12 hours under the impact of westerly wind shear and the front that has descended into the northwestern Caribbean. The net result of these external factors acting upon Tomas is that we now have Tropical Storm TOMAS with sustained winds of 50 mph (80 kph) still moving west by northwest, but also being pushed toward the north. The center of circulation is some 100 miles west of the heaviest rain/storm bands. All of this has increased the degree of uncertainty considerably making it quite difficult to accurately forecast future progress and development of this tropical cyclone, consequently both the projected track and intensity over the next 24 -120 hours may have to be continuously adjusted over the next couple of days.

Currently the forecast is for Tomas to turn north and go over Hispaniola to emerge over the Atlantic and the eastern Bahamas toward the end of this week, after that there is little agreement between the various models, with some predictiong a turn toward the northwest (the USA) and others toward the northeast and the open waters of the Atlantic. The same degree of high uncertanty also applies to intensity forecasts, where the consensus appears to call for some strengthening in 4-5 days, but with wide disparity among the projected maximum sustained winds.

Projected track for tropical cyclone Tomas as of 1 November 2010. The degree of uncertainty for days 3 - 5 is high.


All in all it would appear the only thing certain about Tomas is how uncertain its future progress and intensity really are. We’ll just have to monitor this system closely to see what happens. In the mean time we should also keep an eye toward the east where a tropical wave appears to be growing ovwe Hurricane Alley!

Atlantic-wide satellite view for the aviation industry on 1 November 2010 showing now Tropical Storm Tomas under the impact of westerly shear, and a tropical wave mobing along in Hurricane Alley.