Guest Contributor | Aug 30, 2019 | 0
Weather overview up to 24 June and short-term outlook to Friday 28 June 2019
Visual. Sea Surface Temperature anomalies in the combined Nino 3 and 4 regions in the equatorial Pacific.
Source: Climate Prediction Centre in the National Oceanic and Atmospheric Administration of the US Government. www.cpc.ncep.noaa.gov/products/analysis_monitoring/lanina/enso_evolution-status-fcsts-web.pdf
Overall weather conditions for the entire sub-continent and local conditions for Namibia in particular, are about as static as one can get.
During the past ten days, the daily synoptic pattern has shown a very predictable progression with the only slight anomaly, the pace at which the frontal systems migrate from west to east around Cape Agulhas.
In general, the South Atlantic high pressure cell has taken its time to approach the continent, often lingering five or six days over the sub-continent’s interior before morphing into the southern Indian high. The South African Weather Service’s synoptic map of Monday morning confirms this slow progression, showing a winter stance that only changes incrementally every day.
The lack of local activity is corroborated by the snail’s pace of the current, weak El Nino in the equatorial Pacific. The visual for this week is the so-called Oceanic Nino Index for the past almost 70 years. It is based on a particular region of the equatorial Pacific just east of Indonesia. As a benchmark it is very reliable, not only for its long duration but also because this specific region gets the most attention from the scientific community when researching El Nino La Nina cycles.
The direct link between El Nino/La Nina and wet and dry years in Namibia is not accepted by all meteorologists. In fact there are several leading academics who say this link is inferred and at most tenuous. However, the visual with the dry years marked by a red arrow and the wet years by a blue one, shows unmistakeably that there is a demonstrable connection in at least the majority of years where Namibia either flooded or parched.
Older Namibians will remember the excruciating droughts of 1958, 1966, 1973, 1983, 1998 and 2016. These all fit neatly with the index. Lesser droughts are also confirmed by the index such as 1987 and 2010.
On the wet cycle, the index is not so dependable as a mirror for local rainfall but there is still a strong correlation. The two most noticeable years are 1976 and 2011.
The current El Nino is in its waning phase and the consensus view is that it will remain in place until after the southern hemisphere winter after which is will slowly decay to a neutral stance. For instance, while the eastern Pacific winds have been anomalously weak for the past three months (a typical El Nino phenomenon), they have suddenly picked up over the past fortnight, as can be seen in the colder water moving from east to west. To a relatively certain degree, this is an early indication that in about six months from now, colder surface water will have reached Indonesia, setting the stage for the next cooler phase of the El Nino La Nina oscillation.
From this very long outlook, it does not mean (at this stage), that the end of the year will be wetter than normal and that it will continue into the main 2020 season, but it does indicate a high probability that the next rain season will at least be normal.
On the Radar
The South Atlantic high approaches the continent by Tuesday but is siphoned away at its leading edge by the strong trough ahead of it. This means that very little of the cold behind the frontal system will reach the Orange River.
For the duration of this week, conditions will carry on very much in the same subdued manner. By Wednesday, both the high and cold front have passed the southern Cape, indicating a generally warmer week for Namibia.
At the convergence line between the high’s northern rim and the anti-cyclonic circulation over the rest of the sub-continent, a weak mid-level trough forms that will be present on Tuesday and Wednesday. This will bring a steady north-westerly airflow over the Namibian interior and there may even be a surprising winter cloud or two.
It is only by Thursday evening that the next approaching South Atlantic high comes close to Cape Town, however its front is expected to decay quickly after it has made landfall and by Friday, all that will remain will be windy conditions along the southern Namib and somewhat cooler temperatures over the Karas region.