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Author: Weatherman

The Week’s Weather up to Friday 24 February Five-day outlook to Wednesday 01 March

Precipitation forecast from Friday 24 February to Saturday 04 March Source: wxmaps.org, GrADS/COLA The Inter-Tropical Convergence Zone is by definition an extensive low pressure band that runs around the globe straddling the equator. This band lies between 10°N and 10°S latitidues, thus just over 2000km wide. It tends to be better defined in the northern hemisphere than in the southern because there is more land in the northern hemisphere at that latitude. However, in the austral summer, it wanders far to the south from its usual containment. Then it appears in Africa, South America and Australasia, sometimes as much...

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The Week’s Weather up to Friday 17 February Five-day outlook to Wednesday 22 February

Precipitation forecast from Friday 17 February to Saturday 25 February 2017. Source: wxmaps.org, GrADS/COLA Meteorologists are not known for their humour, their subject matter is far too serious but the South African Weather Bureau drew chuckles from old weather dogs when, on Monday, they described the precursor of Dineo as a “Tropical Disturbance.” It appears, one of the young understudies has never been explained to that TD stand for Tropical Depression. Nevertheless, all the eyes were on the tropical depression in the Mozambican Channel at the beginning of the week. This system developed, almost overnight into a Tropical Storm,...

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The Week’s Weather up to Friday 10 February Five-day outlook to Wednesday 15 February

Precipitation forecast from Friday 10 February to Saturday 18 February 2017. Source: wxmaps.org, GrADS/COLA Tropical storm Carlos east of Madagascar has produced the expected results. Described by meteorologists as a severe storm, its windspeed was recorded at 55 knots about 100km away from the eye. A tropical storm is an intense depression, creating a vortex that may reach as high as 24,000 feet. This mechanism acts like a suction pump or a vacuum cleaner on a massive scale. It carries immeasureable amounts of water vapour aloft leading to a very high so-called vapour load. This is a condition where...

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The Week’s Weather up to Friday 03 February Five-day outlook to Wednesday 08 February

Precipitation forecast from Friday 03 February to Saturday 11 February 2017. Source: wxmaps.org, GrADS/COLA   The South Atlantic high pressure cell remains offshore. The core, measuring a moderate 1024 mB is more than 2000 km away from the continent. It has been in this vicinity since November last year. The only noticeable shift has been southward, first by some 600 km from the Walvis Bay latitude to the Port Nolloth latitude. During January, it made a further transition to the south, with its core now straddling the 40°S latitude. Longitude-wise, it has remained on the same meridian at about 20°W....

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The Week’s Weather 27 January 2017

The week began with a typical mid-summer stance on the synopitc map. Both the South Atlantic high pressure cell and the southern Indian high were in their customary positions, the former offshore the west coast and the latter south-east of Madagascar. Most of the subcontinent experienced low pressure conditions over the interior. The only exception was the mild high pressure intrusion over Namibia from the Atlantic leading to clear and hot conditions in the Hardap and Karas regions. The feauture that demanded attention was the moderately strong trough from western Zambia, across Botswana into the South African interior. A...

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The Week’s Weather

[email protected] A strong divergence between surface conditions and upper level movement, continued into this week. As the week progressed, the impact of the South Atlantic high pressure cell on the surface caused clear skies for most of southern Africa south of the 20° latitude. This is more or less the line running from west to east through Etosha, northern Botswana, southern Zimbabwe and Beira in central Mozambique. The only exception was a weak mid-level trough at the interface between ground and upper levels at the so-called 500 mB surface, around 18,000 feet ASL. The synoptic may at Friday morning,...

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The Week’s Weather

[email protected] The divergence between surface and mid-level conditions east of the convergence zone is the most noticeable feature of this week’s weather development. A weak cyclonic surface circulation was present over Botswana between Ganzi and Mohembo on the southern boundary of Babwatwa National Park. This rotation resulted from the opposing wind flows. One stream of air came form the south, following more or less the Namibia Botswana border while the other came from Zambia in the north, crossing Babwatwa into Botswana. Where the two met, the difference in densities caused a rotation, much like a whirlwind, but only on...

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The Week’s Weather 06 January 2017

[email protected] The first major intrusion from Angola deep into the Namibian interior happened over the past six days. A well-developed low level trough ran from the Kunene river across the North, north-east, the central high ground, and into the Kalahari along the Botswana and South African borders. But the South Atlantic high pressure cell continued to dominate surface conditions as evidenced by the deep inland penetration of the fog belt on at least three occasions. However, the cell was relatively weak with a core reading of 1020 mB so the on-land impact was limited to the western half of Namibia. Where the high’s outer rim encountered the low-level trough, a very wide convergence zone formed with a well-demarcated convergence line running more or less from Okongo in the north, past Windhoek on the eastern side, and down into the Hardap and Karas regions. It was also noticeable that where the cloud base west of the convergence line was around 18,000 feet, east of the convergence line, the lower cloud surface rolled in at about 10,000 feet elevation. The daily rainfall figures published by the Namibia Meteorological Service illustrate best the importance of surface locale relative to the convergence line. Several places from Owambo, through the interior into the Kalahari registered daily falls in excess of 50mm. Most araes east of the convergence line registered a comfortable 25mm or more....

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