- Friday, 04 November 2011 12:54
- Published Date
- John Olszewski
- Hits: 3802
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
- WeatherEl Nino and its driving force, the Southern Oscillation, are back in the news. Not because of their presence, but because of a possible resurgence....WeatherWhat happened? When applying such words as “normal” to weather and climate in our context, the essence of our arid environment must be...WeatherWhat Happened? The presence of a weak lower pressure area over the western half at midweek, both the beginning and the end of the week were...WeatherWhat happened? The gradual approach of the fringes of the tropical airmass has proceeded despite an unfavourable upper air pattern dominating the...25 April 2014 (941 hits)WeatherWhat Happened? After some weeks of zonal airflow indicated on the local synoptic map, the latter part of this week saw a return to the typical...rainfall 06 December 2013 (992 hits)WeatherWeatherWhat happened? That complexity is a part of weathers’ pattern is endemic; not always apparent but is shown on today’s charts with complex vortex...Weekly Rainfall - 30 March 2012 (802 hits)Weather28 March 2014 (564 hits)WeatherWhat Happened? Conditions this week were somewhat anomalous. A prominent high pressure cell developed south-east of South Africa with its core some...08 August 2014 (522 hits)WeatherWhat Happened? Low pressure control of both the surface and the upper air remained the dominant feature of the week. Earlier in the week, the South...
- 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
- HeadlinesAt the dawn of Independence in 1990, the Peace Corps Volunteer relationship between Namibia and the United States started. More than 1500 volunteers...Impending doom for Witvlei (33 hits)HeadlinesWitvlei Meat Managing Director Sydney Martin said this week that the government has not kept its promise of allocating a sufficient quota to its...Paladin’s revenue spikes 79% (40 hits)HeadlinesA downturn in the spot price of uranium has not deterred production at Paladin Energy’s Langer Heinrich operation. Langer Heinrich produced 27%...Weather 23 January 2015 (26 hits)WeatherWhat Happened With the Kaiser’s birthday on Tuesday, folklore has it the rain season only starts now. There may be more truth in this...Editors DeskThroughout this year, the verdict on the Eurozone cardhouse will remain in the balance. If the European Central Bank’s copycat experiment work,...