Tag Archives: tropical storm EMILY

7 August 2011: Looking East

Infrared satellite image, courtesy of NASA, showing remnants of EMILY now reorganized as a tropical depression some 180 kilometers east of Melbourne, Florida in the early morning of 7 August 2011

After a few days of suspense wondering what would become of EMILY, after wind shear and the mountains of Hispaniola disrupted its development and progress, on Sunday 7 August 2011 we now see the remnants of that storm at 150 kilometers or so off the coast of central Florida moving north by northeast on its way to nowhere. As we see what was the fifth named tropical cyclone of the 2011 Atlantic hurricane season move out of our neck-of-the-woods leaving no ill effects behind, this is a good time to reflect on the accuracy of the forecasts issued by the National Hurricane Center (NHC) from the time EMILY was just a tropical wave riding along ‘Hurricane  Alley’, through its period of stationary stagnation before it came over Hispaniola and eventual temporary demise, to its recent regeneration and send-off we are now witnessing. Despite the complexities associated with predicting what EMILY would do and where it would go, the NHC forecasters did an excellent job at interpreting the various model outputs and the complex environment surrounding the storm to actually provide what in retrospect was quite an accurate forecast. In fact in reading the NHC forecast discussions we have learned that at least one model actually predicted the dissipation of EMILY as it interacted with the terrain of Hispaniola and southwesterly winds. Short term prediction being one of the key tools at our disposal in our annual bout with cyclogenesis, it is encouraging to see such a good performance during this latest of 2011 cyclones and to know that NHC’s objective is to continue to significantly improve the accuracy of its predictions within the next few years.

So what happens next? Now that EMILY has come and gone, what can we expect from the remaining 115 days or 62.8% of the official 2011 Atlantic hurricane season?

NOAA had called for a 2011 Atlantic season that will exceed the 11-6-2 [named-storms, hurricanes, major hurricanes] averages of past years, but just yesterday this agency also increased its predictions to the upper region of the ranges based on a number of criteria including the levels of sea surface temperatures across the entire tropical Atlantic basin, and the possible re-emergence of a currently neutral La Nina event off the Pacific coast of central South America.

In a recent posting [ see 2011 Atlantic Hurricane Season: a New Level of Activity Ahead posted on 7/27/2011 in www.mitigat.com] in addition to the contributors to cyclogenesis identified by NOAA in calling for an above-average 2011 season, I also pointed toward the larger combined environment consisting of the Indian Ocean, equatorial Africa and the eastern Atlantic as an important factor to consider relative to how active the remainder of the 2011 Atlantic hurricane season might be.

Today, on 7 August 2011, I again see activity in the so-called “tropical-wave assembly line” over equatorial Africa, which could be an indication of potential cyclonic activity in the future as the 2011 hurricane season continues to develop.

Color-enhanced infrared satellite image on 7 August 2011 showing a tropical wave over the eastern Atlantic, just south of the Cape Verde Islands. moving west toward 'Hurricane Alley'

In looking east, today we see a strong tropical wave that has recently emerged over the warm surface waters of the eastern Atlantic to the south of the Cape Verde Islands, which is moving west to ride ‘hurricane alley’, while other tropical waves farther east over equatorial Africa follow right behind. Beyond Africa’s eastern coast there is plenty of activity over the northern Indian Ocean and the Arabian Sea that translates into the pulses of disturbed weather that will regularly feed into the ‘tropical-wave assembly line’ to be carried westward toward the eastern Atlantic, and ‘hurricane alley’. This regime of tropical pulses evolving into tropical waves over equatorial Africa, which may actually feed into ‘hurricane alley’ in the Atlantic, appears to have become better organized and stronger over the past couple of weeks ensuring a continuous supply of “seeds” for cyclogenesis in an area of the tropical North Atlantic that is conducive to such development. If NOAA’s forecast of a resurgent La Nina holds we will then have another external trigger to contribute to potential cyclogenesis in the Atlantic during the remainder of the 2011 season. La Nina acts as a suppressor of wind shear in the Caribbean and central tropical Atlantic resulting in more favorable conditions for tropical cyclone generation in the basin.

Satellite image for the aviation industry on 7 August 2011 showing some of te tropical wave over the eastern Atlantic, and equatorial Africa, mentioned in the text

The tropical wave over the eastern Atlantic, just south of the Cape Verde Islands appears to be well organized with strong embedded storm cells as it moves westward toward ‘hurricane alley’. In my opinion this system warrants closer monitoring in days to come for potential cyclonic development. An even larger and stronger well organized tropical wave following some 800 kilometers to the east, should also be monitored closely in days to come. The satellite image below, courtesy of NASA, shows a close-up of the tropical wave now over the eastern Atlantic.

Infrared satellite image showing a close-up of the tropical wave over the eastern Atlantic, near the Cape Verde Islands, on 7 August 2011

Elsewhere in the northern tropics we have a rapidly dissipating tropical storm EUGENE moving west by northwest over the Pacific away from the coast of Mexico, tropical storm MUIFA now in the Yellow Sea affecting China and the Korean Peninsula, and out over the west-central Pacific typhoon MERBOK some 1500 kilometers east of Japan is now recurving toward the north and northeast aiming  for the Kamchatka peninsula and the western Aleutian Islands. All of these currently active cyclonic systems are shown in the satellite images that follow:

Satellite image, courtesy of NASA, in the early hours of 7 August 2011 showing tropical storm EUGENE moving away from land over the eastern Pacific
Satellite image, courtesy of NASA, showing an infrared view of tropical storm MUIFA in the Yellow Sea on 7 August 2011
Infrared satellite image, courtesy of NASA, showing typhoon MERBOCK on 7 August 2011 moving over open waters of the Pacific as it headed toward the Kamchatka peninsula and western Aleutian Islands

2011 Atlantic Hurricane Season: Where will Tropical Storm EMILY go?

Infrared satellite image of Tropical Storm EMILY in the morning of 1 August 2011 as it moved toward the west in the eastern Caribbean

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:

Satellite image showing water-vapor in the atmosphere on 2 August 2011 showing Tropical Storm EMILY in the eastern Caribbean and the surrounding environment that will help guide the cyclone's progress in coming days

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!!

RECENT ACTIVITY

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:

Infrared satellite image of Tropical Storm EMILY on 2 August 2011 at 18:45 taken after the storm had renewed its forward motion on a new track toward the west-northwest, after it had become stationary earlier during the day