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29 November 2013

What happened?
For the last couple of weeks we have entered the time range where the number of sunshine hours per day, far exceeds the night hours. This leads to hot conditions over the central plateau covering two thirds of Namibia, basically the whole Botswana, a large chunks of western Zimbabwe, western Zambia and southern Angola. This heat creates a marked low pressure area which draw in airflow from the adjacent high pressure areas over the south Atlantic and south of Madagascar.

It remains with Namibia until April by which time some 90% plus of our expected rain will have been measured. Over the next 120 days, we will be expecting the bulk of the rain for the entire season, and indeed for the whole year.
The “season” 2014 has got itself quite promisingly into activity. Across much of Namibia, clouds have formed within a favourable air-mass and showers have been recorded.
Taking the text book example of how the weather pattern builds, we have seen a typical example of the early season development. The positioning of the various influential synoptic patterns, influence of their air-flows and the forthcoming results have matched this the expected pattern. This may be indicative of a more positive season later on, but it is too early to tell.
Perhaps as a bonus, the climate change aspect has brought the Congo Air-mass presence and its activity potential somewhat more into focus. Not all the necessary features have formed to make their mark, it is still early in the “season” range, but developments bode well.
On every day of this past week, some or other part of the country has enjoyed rain. The spread has varied with the various synoptics, but the ability has persisted.
The various synoptics have seen the consistent anticyclonic presence hold sway from the 35 to 45oS latitudes, pushing cold fronts with a limited northward extension, building the succeeding ridge into a new core on the southwest Indian Ocean. This pattern maintained a consistent moist inflow across the eastern sub-continent: again a textbook sample for the time of year.
Such a pattern has brought widespread but light rain within the variable band from our northern borders down to the southern interior. Occasional heavier falls have been reported, quite typical for this developing pattern.

What’s coming?
For yet another week, the overall pattern keeps the daytime heat-low hovering above our south with some eastward extension. To the north and east a moist presence will allow quite widespread cloud presence. Convective activity continues on a daily basis, but marked convergence appears limited. The very limited level of synoptic intrusion from whatever cause or source, will allow local  convective activity to vary in response to local activity. The overall synoptic pattern indicates positive rainfall expectations for most of the country, for most of next week, but the actual showers will be sporadic.

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