Tropical Storm EMILY, the fifth-named cyclone of the 2011 Atlantic hurricane season, appears to have stalled on its track in the eastern Caribbean earlier today. Whenever a tropical cyclone ceases to move it becomes increasingly difficult for the various predictive models to produce a reliable forecast. This illustrates some of the difficulties forecasters at the National Hurricane Center – Tropical Prediction Center have to deal with as they strive to provide accurate forecast that will be of help in protecting life and property in vulnerable communities.
The track that Emily followed, over several days, from the eastern Atlantic along ‘Hurricane Alley’ until it coalesced out of a grouping of disorganized tropical waves into an elongated conglomerate of storms cells that began to get organized as it neared the Lesser Antilles just a few days ago, is typical of the type of tropical activity that we see every year as the so-called hurricane season develops and matures over the course of several months.
However it is important to stress there is no such a thing as a “typical” hurricane. In reality what we must deal with is a collection of “typical” components that are contributors to cyclogenesis, but which must be considered on a case by case basis as cyclones in the making, together with several other factors that are part of the coupled atmosphere-ocean environment that influence the development of each of those potential cyclones.
In the case of EMILY, there are already several potential contributors active in the atmosphere-ocean environment surrounding the current location of the cyclone and also ahead of it. One way in which the various potential contributors to cyclogenesis can be visualized is by looking at satellite images using filters to detect water vapor in the atmosphere, as this helps illustrate the main forces that will be guiding or steering the progress of the cyclone. Take a look of a resent water-vapor satellite image of the Caribbean basin taken on 2 August 2011, below:
In viewing the satellite image above, the presence of water-vapor in the atmosphere helps us actually see large regions of dry air both to the north and west of Emily’s current location, which would act as deterrents to precipitation as the system moves forward. Also easy to visualize is a weather front progressing along the coastal USA toward the south-southeast, which could act as a barrier to northward movement by the cyclone helping steer it toward the northeast as the two systems start to interact in the next couple of days.
The satellite image also shows the Antilles and other land masses ahead of the predicted track for Emily. At this point it is important to try and visualize what may happen as the cyclones comes over land and interacts with topography, which in some cases includes 3,000 meter-high mountains.
From the above rather summarized discussion it is clear that forecasting where EMILY will eventually go over the next 2 – 5 days, requires constant attention to a wide range of potential contributors all acting simultaneously to influence not only the actual track followed, but also the size and intensity of the cyclone itself. In summary, nothing short of continuous monitoring and analysis will do to provide as accurate as possible a forecast.
Let us all pay attention, be prepared and practice MITIGATION!!
After I had originally posted the above piece EMILY started moving forward again while also moving in a new direction, toward the west-northwest, which will take it in the direction of Santo Domingo, in the Dominican Republic. This new track and movement has allowed the model to provide a new forecast, which is shown below:as of 2 August 2011 at 17:00″]This latest track forecast clarifies some of the uncertainty that was present earlier today. For starters it appears to bring the cyclone on a track that will traverse Hispaniola along the mid-section of the Dominican Republic with a higher chance for interaction with mountainous terrain, which should contribute to a much weaker system as it emerges over the waters of the Atlantic, if indeed it manages to maintain enough momentum and organization to survive and remain as a tropical cyclone after its transit over the island. It also appears that this new track will take the storm over the western Bahamas rather than the Florida Straits, which would be good news for South Florida as this would mean a weaker storm, farther away from Florida’s coasts than originally projected.
It is important though, in assessing above analysis, to keep in mind the uncertainties that are inherent with this type of forecast and also the margin of error associated with a projected track, which grows larger the farther you go into the future.
Below is an infrared satellite image [courtesy of NASA] showing a much better organized tropical storm EMILY as of 18:45 on 2 August 2011: