Tag Archives: Tropical Storm LEE

2011 Atlantic Hurricane Season: Was that it?

Although the historical record shows there have been Atlantic Basin tropical cyclones in every month of the year the “official” Atlantic Hurricane Season runs from June 1 through November 30.

GOES satellite image showing a good portion of the tropical Atlantic basin on 4 December 2011

So, today being Saturday 3 December 2011, we could say that “officially” at least the 2011 Atlantic Hurricane Season is over. The question is: does mother Nature agree?  Looking at various satellite images from around the world, but well aware of the caveat that nature is quite capable of surprising us and that change is a constant of nature, there is an absence of the triggers and contributors in the regions that usually lead to cyclogenesis in the Atlantic basin. On that basis I would say the 2011 Atlantic hurricane season does appear to have come to an end.

Color-enhanced infrared satellite image of a partial North Atlantic basin on 3 December 2011 showing the large regions of high pressure and dry air that prevail over much of the basin

There are no tropical waves or cells of disturbed stormy weather over the region of Equatorial Africa designated as the tropical-wave assembly line. Nor do we see any seeds for potential tropical cyclone development along hurricane alley, the Atlantic Ocean corridor reaching from the western coast of Africa near the Cape Verde Islands to the Lesser Antilles and the eastern Caribbean.

GOES satellite image showing large sectors of high atmospheric pressure and dry air and the absence of tropical waves or any other cells that might qualify as seeds for tropical cyclone development

A very large bubble of high atmospheric pressure and dry air has prevailed over the Gulf of Mexico and most of the Caribbean sub-basins, as well as along most of the USA Atlantic seaboard and adjacent Atlantic coastal waters., which has prevented any sort of tropical weather from developing or penetrating the region.

Composite of satellite images creating a global view of the northern tropics from the eastern Pacific to the Indian Ocean on 3 December 2011

The composite global mosaic of satellite images shows a large swath of the northern tropics from the eastern Pacific to the northern Indian Ocean that on 3 December 2011 was basically clear of any disturbed weather, or tropical waves. Likewise a full-disk composite satellite image of Earth’s Western Hemisphere shows a disrupted belt of tropical activity from the coast of western Africa, north of the equator, pretty much all the way to Hawaii except for some stormy weather over the Andes and other mountains in northern South America.

Composite of satellite image give a full-disk view of Earth's western hemisphere on 3 December 2011; notice the absence of the belt of tropical activity that regularly girdles the planet near the equator

In fact the only potential for tropical cyclonic activity worldwide is in the southern Indian Ocean where two tropical waves, one south of the Indian subcontinent and the other to the northeast of Madagascar, are showing some organization and plenty of stormy weather over warm waters that may lead to future tropical cyclone generation. Other than these specific cells all remains quite on the tropical front.

Color-enhanced infrared satellite image of the Indian Ocean on 3 December 2011 showing the only two cells of disturbed weather with some potential for cyclonic activity on a worldwide basis

What kind of a season was it in 2011 in the Atlantic basin? With a total of 18 named storms the season qualifies as quite an active season, certainly a continuation of the multidecadal period of increased activity that started in 1995. However only 6 storms reached hurricane strength and of these, only 3 became major hurricanes [ category 3 or higher in the Saffir-Simpson scale] and in this sense it was a below-average season. But if we assess the death toll, injury and damage caused by land-falling storms or hurricanes that otherwise affected land, the 2011 Atlantic season clearly ranks way above average based on a death toll that included at least eleven in New Jersey and six in Vermont, more than $7.0 billion in damages  and the worst flooding seen in the USA Northeast in more than 80 years. The negative consequences of the 2011 Atlantic hurricane season were made even worse when tropical storm Lee followed in hurricane Irene’s footsteps contributing additional intense rain from Virginia to Vermont where already saturated soils could not keep up with the pace of precipitation exacerbating flood conditions throughout the region.

The above reinforces the point that it only takes one impact by a tropical cyclone to cause plenty of damage and human suffering. Also, in terms of damage, it does not have to be “the big one” meaning a monstrous category 5 with extreme winds pounding a region; a lot of damage can be caused by what could be classified as a minor hurricane, but one that carries a lot of water in it as was the case with Irene.

If we assess the 2011 Atlantic hurricane season in the context of tropical cyclone activity on a worldwide basis so far in 2011, it is interesting to note that we are seeing a repeat of  what happened in 2010 when the total number of named storms worldwide was close to 17% below average. So far in 2011 there have been a total of 65 named tropical cyclones  worldwide, including the 18 that generated over the Atlantic. With  only a few days left before the end of the year and little potential for cyclogenesis in the near future, based on current atmospheric conditions worldwide, it appears we will end the year with another below-average global season.

While two consecutive years of below-average tropical cyclone activity on a global basis do not signify a trend one can not, but ask if this might not be a signal from Nature telling us that the threshold for cyclogenesis has shifted to a higher level, in response to global warming? In my opinion the multidecadal cycle of increased cyclogenesis in the Atlantic is masking this possible shift in the threshold for tropical cyclone generation in this basin, while elsewhere in the world we continue to see fewer storms. Certainly food for thought and an important area for research exists relative to tropical cyclone activity on a global basis, and how this is being affected by global warming or others aspects of global climate change.

Relative to this topic it is critical to keep in mind that what really matters is our own relative vulnerability to tropical cyclones in the community where each of us lives, because it is the impact at the local level that can bring death, injury, damage and human suffering, regardless of whats happens during a season in a given basin or of what may be happening on a global basis in response to global warming. All it takes is one impact. We must pay attention, be prepared, and above all we must practice mitigation!

Could it be #13 over the horizon?

View of the southeastern USA and adjacent Atlantic waters from the GOES satellite, on 5 September 2011, showing tropical cyclones KATIA and LEE

An active month of August, in tropical cyclone terms, is over and now as we move forward into September the  most active month of the season, based on the historical record, a few things are happening in the Atlantic basin.   Tropical storm LEE continues its rather slow march toward the northeast dumping copious rain over Louisiana, Mississippi, Alabama, Tennessee, the Florida panhandle, Georgia and the Gulf of Mexico. KATIA is once again a hurricane as it moves northwest and begins a slow turn to the north and eventually the northeast.

Color-enhanced infrared satellite view of most of the tropical Atlantic basin where in addition to active tropical cyclones KATIA and LEE we also see a large tropical wave moving westward along hurricane alley

Looking east toward the far-away eastern Atlantic, there is a large tropical wave some 500 kilometers southwest of the Cape Verde Islands moving westward over hurricane alley, which appears to be getting stronger and better organized as it progresses toward a favorable environment of warm waters and low wind shear ahead. Will this be the 13th named tropical cyclone of the 2011 Atlantic hurricane season? Where will it be two or three days from now? How intense will it be then? Does it pose any threat to the USA? These are all valid questions, which meteorologists and scientists at NOAA will be trying to answer as they monitor and track this system in order to issue three and five-day forecasts once, and if, this system becomes a tropical cyclone. For now suffice it to say that the National Hurricane Center and other divisions of NOAA are already watching this specific tropical wave closely, and so will we.

Atlantic-wide water-vapor satellite view showing tropical cyclone activity on 5 September 2011

In fact, we will continue monitoring this specific tropical wave so that we can report any development that could be of interest to vulnerable communities in the Caribbean and Gulf sub-basins, and in the coastal USA along the Atlantic. Toward that end we will also continue to keep an eye on the rest  of the tropics in the Atlantic and on a worldwide basis to share any knowledge gained from our observations.

Composite full-disk satellite view of Earth's western hemisphere, on 5 September 2011, showing a disconitnuity in the so-called 'belt of tropical activity' that normally circles the planet this time of the year

Speaking of sharing knowledge, I believe it is interesting to share that today there appears to be a “break” in what I have named the belt of tropical activity that usually circles the entire planet during the northern hemisphere summer. We had seen a branching of the belt earlier this year, with a secondary branch going off toward the northwest and then north over the central Atlantic. Today, 5 September 2011, we see that same “branch” chasing after Hurricane Katia, but there is also a cut-off of the belt in the middle of hurricane alley leaving a discontinuity all the way to northern South America where the belt starts again and continues around the Pacific and beyond. I believe this specific condition is a reflection of how active the tropics have been this year, while it also highlights the difficulties associated with forecasting where one specific storm will go or how strong it might be five days from now, which in turn makes us all admire how accurate most predictions of Atlantic tropical cyclones’ center tracks have been in 2011 as well as how much track predictions have improved in accuracy over the past ten years.

Relative to how much NOAA’s hurricane center-track forecasting has improved in recent years, and how such improvement contributes to much more effective decision-making by the emergency management community in hurricane-vulnerable communities along the coastal USA, I found it somewhat disheartening that some media chose to highlight the somewhat inaccurate forecast of the intensity of Hurricane IRENE as it approached the northeastern USA rather than the quite accurate track forecast that allowed many communities to avoid evacuations of the coastal region and many more to prepare with plenty of time for the upcoming impact. This only shows how much there is still to learn about what an impact of a hurricane really means, and how the fixation on a number in a scale can be so misleading with respect to what damage to expect from the impact of a hurricane. We certainly have seen our share of “minor” hurricanes or “just a category 1”, so-called by the media, which have caused enormous damage and unheard of human suffering. In fact hurricane IRENE is one such example; as of today damages have reached more than $13.0 billion, the death toll is nearing 50, and close to 1.0 million residents along 13 states still remain without electrical power on this 2011 Labor Day. I would argue the media would do well in learning more about what we all need to do to improve how to inform a vulnerable public about what the impact of an approaching hurricane could bring to a given community, something that the Saffir-Simpson scale was not designed to do, rather than on the difficulties that remain in hurricane-intensity forecasting. NOAA is the first to acknowledge that much work remains to improve intensity forecasting, and it is working hard in continuing to improve in this regard.