- Friday, 04 November 2011 12:54
- Published Date
- John Olszewski
- Hits: 3631
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
- Rainfall 24January 2014 (610 hits)Weather28 August 2014 (129 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...04 April 2014 (489 hits)WeatherWhat Happened? A seasonal anomaly, very visible on sea-surface-temperature maps, is the large variance in temperature over the south-western Indian...WeatherWhat happened? With the gradual transition from autumn to winter in the southern hemisphere, a more typcial (expected) weather pattern is slowly...Weekly Rainfall - 12 April 2013 (435 hits)WeatherWeatherWhat happened? Weather’s ability to switch patterns with little warning is its prerogative, weather watchers have the equal prerogative of hourly...WeatherWhat happened? A week ago, there was the prospect of a colder weekend coupled with an active, but mobile, vortex lying just south of the Cape. This...Rainfall 25 April 2014 (692 hits)Weather25 July 2014 (577 hits)WeatherWhat’s Happening? The US government climate agency, known best by its acronym, NOAA, still indicates current conditions over the equatorial Pacific...Weekly rainfall - 16 March 2012 (740 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 winner of the Best Business Idea competition run by the Economist Businesswomen Club after their Businesswomen Conference in Ongwediva, was...Ostriches back in vogue (38 hits)HeadlinesThe most discredited agricultural commodity, ostriches, are back on the farming radar after the Ministry of Trade and Industry, in collaboration with...Editors DeskCan one imagine how unmanageable the Namibian capital market would be if yields on government bonds came down by 11% on one day, only to jump up more...17 October 2014 (34 hits)WeatherWhat Happened? The layered atmospheric sandwich that started developing last week continued up to Wednesday this week at which point the last...Namibia commemorates World Food Day (47 hits)HeadlinesThe City of Windhoek commemorated World Food Day yesterday at Otjomuise. This is the first ever commemoration of the World Food Day in Windhoek and...