Annular Solar Eclipse – 2016 September 1

 

Figure 1: Path of the central eclipse across southern Afruca,
Figure 1: Path of the central eclipse across south and central Africa. Eclipse track: Xavier Jubier.
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Weather Resources for Eclipse Day

 

Africa Eclipse

The eclipse track enters the African continent just south of the equator, passing across the low-lying Congo River Basin as it traverses Gabon, The Congo, and the Democratic Republic of the Congo (DRC). The climate in this part of the continent is marked by two rainy seasons, separated by intervening dry spells. The rainy seasons are tied to the overhead passage of the Sun, and so locations at low latitudes tend to receive their maximum rainfall in the months following the equinoxes. In Gabon, the “big wet” peaks in October; in Brazzaville (The Congo), it is in November. Dry weather comes in June, July, and August. Since this eclipse comes on the first day of September, the wet season is underway, but has hardly begun.

Unfortunately, dry weather does not translate into sunny weather, at least over the Congo Basin, and September skies are not very promising, as can be seen in the statistics in Table 1. The percent of possible sunshine averages around 40 percent in both Gabon and The Congo (no climate statistics are available for the DRC).

As the track moves southward into Tanzania, there is an almost magical change in weather prospects. By this time, the track is far enough to the south that the double wet season has all but disappeared. Across Tanzania, Mozambique, and Madagascar, the dry season expands across the months from May through October, placing the eclipse at the driest time of the year. The clouds cooperate too, with station observations reporting up to 85% of the maximum possible sunshine in the month. These numbers are comparable to the best that can be found anywhere for an eclipse. Part of explanation for the sudden change in weather lies in the topography of the region, particularly the Mitumba Mountains along the DRC-Tanzania that block the flow of moisture from the Congo Basin and the altitude of the East African Plateau border in Tanzania.

Figure 2: Average fractional September cloud cover based on satellite observations 1989-2009. data: Patmos-x/CIMMS/University of Madison-Wisconsin.
Figure 2: Average fractional September cloud cover based on satellite observations 1989-2009. data: Patmos-x/CIMMS/University of Madison-Wisconsin.

 

To single out the very best sites to watch the lunar shadow, we can  turn to the maps of satellite cloud cover observations (Figure 2), which display two areas of very favourable eclipse-viewing cloudiness. In Tanzania, it is the region between the Mlala Hills on the east side of Lake Tanganyika and the Kipenrege Range to the north of Lake Nyasa (Lake Malawi). Eclipse watchers may wish to settle on Katavi National Park or on the centre line north of Mbaya.

Table 1: Cloud and sunshine climate statistics for sites along the eclipse track. The "Percent of Possible Sunshine" is the most reliable indication of the probability of seeing the eclipse.
Table 1: Cloud and sunshine climate statistics for sites along the eclipse track. The “Percent of Possible Sunshine” is the most reliable indication of the probability of seeing the eclipse.

Madagascar

The second exceptional eclipse-viewing area is on the island of Madagascar. On Madagascar, we see the dramatic effects of the prevailing easterly trade winds, which bring Indian Ocean moisture and a cloudy climatology against the windward eastern slopes. The air is compelled to rise, cooling until saturated and forming clouds. Once the moist air flow crosses the high terrain that forms the backbone of the island, it descends toward the coast along the Mozambique Channel, warming and drying as it returns to sea level. At Mahajanga, on the Africa side of the island, the percent of possible sunshine is over 85% (Table 1), among the highest anywhere along the eclipse track. At Toamasina, on the Indian Ocean side, the percent of possible sunshine falls to 59%. Travel is difficult in coastal regions of Madagascar, as numerous river deltas carve the terrain into impassable sections, and so a slightly inland location is probably preferable, perhaps where the track passes south of the Ankarafantsika Nature Reserve.

Table 2: Temperature and precipitation data for sites along the eclipse track.
Table 2: Temperature and precipitation data for sites along the eclipse track.

 

Even though the most favourable sites are identified as being in Tanzania and Madagascar, the conditions in coastal Mozambique cannot be entirely ignored. Surface observations at Pemba, on the Mozambique coast, show a percent of possible sunshine that slightly exceeds 85%, a value bested only by Mahahanga, and even then, by only a tiny amount.

Reunion

On Reunion, the observed cloud statistics in Table 1 gives the nod to the airport at Pierrefonds and the Saint-Pierre neighbourhood, which lie on the south side of the island.  This more favourable cloud is caused by the drying flow of the prevailing northeasterly trade winds as they descend from the volcanic calderas of Piton des Neiges and Piton de la Fournaise into la Plaine des Cafres. The best weather conditions will be found just about anywhere within the Plaine des Cafres, but the south coast, from Saint-Pierre to Saint-Joseph will place you closest to the central axis. Because of the low altitude atcentral eclipse, some attractive photographic possibilities might be had within the calderas and the inland reaches of the Plaine.

Those eclipse seekers who travelled to southern Africa and Madagascar in June 2001 will find the weather at this eclipse to be very similar though slightly later in the season. Most eclipse parties enjoyed spectacular success in 2001 and there is every reason to expect that a similar experience will reward travellers in 2016.

 

Updated August 2016

Climatology and weather for celestial events