- Friday, 04 November 2011 12:54
- Published Date
- John Olszewski
- Hits: 4073
This past week an unusual synoptic pattern has held sway across the southern hemisphere. A major anticyclone with core pressures well above 1030hPa straddled the Date Line (180o) in the south Pacific while on our side, a complex low pressure pattern covered most of southern Africa and the southern oceans.
Both high and low pressure systems have been static for this period. Static in position but active within themselves: anticyclonic strength ensured a consistent flow to maintain La Nina’s, positive oscillation, and dominance of global weather.
The complexities of the vortex areas see one core deepen, drift somewhat eastward while in the cold, unstable polar air behind it a secondary vortex quickly forms, weakening the older core, then the same cycle is repeated. The effect of this pattern maintained a zonal flow throughout the troposphere (surface to 40000 feet) above southern Africa.
The unusual feature is that these differing systems have held their geographical placing while whatever else may be on the weather map either by-passes or collapses while these two major systems remain.
The other unusual feature is the global situation on either side of globe: the high and the low. Again, the effect saw a limited, if not absent, eastern Atlantic anticyclone, and similarly an absence of the western Indian Ocean anticyclone.
This departure from the norm means there is no lower level moisture input from the Indian Ocean, so with no push from the east, the heat-low pressure belt across southern Africa remains static ensuring that over Namibia there has been an advection of bone dry southerly air. This limits daytime temperatures but with no anticyclonic thrust it cannot undercut the heat-low. Without convergence, there is no cumulus cloud and no rain!
The thin layer of cloud visible has too little moisture but its presence offers hope for improvement as November wears on.
The vortex pattern persists. The weak South Atlantic anticyclone remains limited throughout the period and because there is little ability to ridge round the continent, any development of a cell away to the east is restricted. Any prospect of late Spring showers depends on the persistent heat-low generating an upward convective extension to tap the adjacent moister air mass gathering above much of Zambia, linking with the equally adjacent Congo air mass then to advect this combination into our Kavango area or further west.
Current outlooks show a mixed set of patterns across the northern mid-subcontinent. Much of the data available is based on satellite images showing cloud coverage and direction of movement. Other observational sources in that area are, largely, non-existent. This data provides the grist from which computer models are built. Otherwise, it is up to a weather observer to assess what is seen to be present and offer an outlook regarding what the current situation will be able to evolve. The heat factor is seen to be increasing and its effects, as outlined earlier, offer a prospect of showers into the new week. n the south west, temperatures will be considerably cooler with a fresh southwesterly wind as a result of the high ridging in from the south Atlantic.
- Articles In This Category
- WeatherWhat happened? What do we believe: our eyes or our charts? For long years, centuries in fact, mankind’s navigators only had eyes, then came...28 August 2014 (229 hits)WeatherWhat Happened? Three cold fronts passed the Cape in quick succession on Tuesday, Wednesday and Friday this week. None of the three was particularly...07 February 2014 (481 hits)WeatherWhat Happened? Generally a drier week than last week as seen in the recorded rainfall for the seven northern regions, but Omaheke is the glaring...Weekly Rainfall - 17 January 2013 (478 hits)Weather31 Oct 2014 (175 hits)WeatherWhat Happened? Conditions this week were fairly conventional for this transitional period between the seasons. At the beginning of the week, the...Weekly Rainfall - 22 June 2012 (1281 hits)WeatherWeekly Rainfall - 23November 2012 (416 hits)WeatherRainfall 09 May 2014 (995 hits)WeatherWeekly Rainfall - 22 February 2013 (387 hits)WeatherRainfall 04 April 2014 (478 hits)Weather
- Related Articles
- WeatherWhat happened? At an unusual time of the year we have seen, one way or the other, a departure from synoptic patterns prevalent across the southern...WeatherWhat happened? That the world’s weather patterns are at odds with themselves seems to be a common consensus. Primarily the cause is to be...WeatherWhat happened? We have seen an interesting hiatus in the development of weather patterns variously around the world as year 2011 progressed. Seasons...WeatherWhat happened? Summer begins with December. From one aspect at least, a start is made to summer as pressure patterns move toward a summery stance....WeatherWhat happened? This week was marked by a cut-off low over the Orange River in the south and a broad trough of tropical moisture moving in from Angola...
- Latest Articles
- HeadlinesThe Economist Businesswomen Projects officially launched the Namibian Businesswoman of the Year Award 2015 this week announcing that nominations are...Xaris MD hits back at allegations (32 hits)HeadlinesSince the announcement that energy company, Xaris won the tender for the construction of a 250mW power plant in the Erongo Region, Nampower and in...Editors DeskThe Chamber of Mines 2015 Mining Expo and Conference took place this week at the Safari Hotel conference centre in Windhoek. The expo attracted just...Weather 22 May 2015 (19 hits)WeatherWhat Happened The synoptic map was dominated this week by an array of high pressure cells covering the southern Indian Ocean, the ocean south of...Xaris to meet deadline (81 hits)Mining & EnergyThe Xaris power plant which is curently in the planning phase will meet its June 2016 deadline according to Xaris Managing Director Hennis Steyn who...