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Weather on the other side of the world

Apr 9, 2013
Figure 1

Figure 1

Sometimes our weather picture can get very localized. We can become a little too focused on our immediate surroundings. I decided to take a wider look around the world to see what was going on. One way to do this is to look at some of the “full disk” satellite images, which are photos that show a nearly full hemispheric view of the earth. There are several such images available. Two are produced by U.S. satellites, one covering the central and eastern U.S. and the western Atlantic as well as South America, and another covering the central, eastern and southern Pacific and the western U.S. One is produced by the European Space Agency which covers the central, eastern and southern Atlantic, Europe, then middle east and Africa, and the Japanese Meteorological Agency produces two images, one for the western Pacific, eastern Asia and Australia, and another which covers central Asia, the Indian Ocean and much of Africa. These images are all available at the following link: http://www.goes.noaa.gov/ataglance.html

Figure 2

The last of these images caught my attention as showing something interesting, although not terribly unusual. In Figure 1, almost right in the middle of the image, a tropical cyclone is quite evident. There is another system which doesn’t look quite as well organized farther to the east, just to the south of the Indonesian island of Sumatra. Also of interest on the photo is the clear view of the Himalayan Mountains. While there are some clouds over portions of Pakistan, Iran and Afghanistan, there are no clouds north of India. All the white that shows up on the photo in this region is snow on the tops of the mountains, and this clearly defines the mountain chain.

I then looked to find more information about the tropical systems, and my first stop was the Joint Typhoon Warning Center based in Guam (www.usno.navy.mil/JTWC/), which has responsibility for tropical systems in this part of the world. By visiting this website, we find that the tropical cyclone in the middle of the satellite photos is named Imelda, and at the time I visited the website, it had top sustained winds of 40 knots, making it a tropical storm. It is forecast to reach hurricane strength at the 36-hour forecast time. Looking at the tropical cyclone graphic (Figure 2) we can see that Imelda is forecast to move generally west, and then turn south later in the forecast period while becoming stronger.

Keep in mind that this is a southern hemisphere system, so it has a clockwise circulation (opposite of the northern hemisphere) and a typical path for a tropical cyclone in this part of the world will carry the system westward to the north of a subtropical high, and often a turn poleward, or toward the south occurs at some point (a poleward turn for a northern hemisphere system would be to the north). Indeed, that is what the forecast shows for Imelda.

Looking into the system farther to the east near Indonesia, there are no advisories being issued for this system at the time of the satellite photo, but by clicking on the links under the Indian Ocean header, we find that the meteorologists at the Joint Typhoon Warning Center have assessed this system as having a medium chance to develop into a tropical cyclone. It is currently early autumn in the southern hemisphere, so the presence of these tropical systems is not at all unusual.

Figure 3

Back to Imelda, I next examined the region of the forecast track of the system to see about any impacts on land areas. Diego Garcia and the small islands of the Chagos Archipelago are located northeast of the initial position of Imelda, and with the system moving west, it does not appear that there is any threat for those islands. However, the Republic of Mauritius and La Reunion Island could be threatened. La Reunion (technically part of France) is shown on the tropical cyclone graphic (Figure 2) and Mauritius is part of the same island group and is located east of La Reunion. Notice that both of these locations fall inside the shaded area on the graphic, which indicates the “area of uncertainty,” and is determined by adding average forecast error statistics at the forecast times to the corresponding forecast of 34-knot wind radius.

As it turns out, Mauritius has a national meteorological service (http://metservice.intnet.mu) so I went there to see what information was available. By clicking on the various links on the website, I could determine that at the time of the satellite photo and the warning graphic from the Joint Typhoon Warning Center, the Mauritius Meteorological Service had not issued any warnings for Imelda. Given that any potential impact is many days away for this area, this is not unreasonable. Other resources are available on this website, including a higher resolution color satellite photo of the region (Figure 3) and a surface synoptic chart (Figure 4).

The synoptic chart shows a large subtropical high center near about 37S/70E with its circulation extending well north into the tropical latitudes, and Imelda is shown on the chart as well, referred to as “MTS Imelda” which stands for “Moderate Tropical Storm.” The turn of the system to the south which is forecast to occur will carry the system along the western end of the subtropical high. Remember that the circulation around highs in the southern hemisphere is counter-clockwise, so the surface windflow in this region would be from the north.

Figure 4

This is simply an example of how much weather information is available to us from all around the world. Anyone who is contemplating an ocean voyage in far reaching areas of the globe would do well to spend some time looking around on the Internet to see what is available in the region(s) where passages are planned. And perhaps some will be spurred on to follow these tropical systems through the next several days to see how they evolve.

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