Author: Weatherman

Bar Chart: ENSO Outlook as at 14 September 2017 showing highest probability for La Nina conditions from November 2017 to March 2018. Source: ENSO update prepared by the Climate Prediction Centre in the National Oceanic and Atmospheric Administration of the US Government.   The second Ice Angel passed through the land this week and the third will be here on Monday. This piece of German folklore best illustrates that repetitive cold intrusions in October are not the exception and have been recorded for about 150 years. Namibian weather is always determined by the interplay between the cold, high pressure...

Synoptic Map: Barometric pressure and surface conditions as at 06:00 Thursday morning. Source: South African Weather Service Thursday’s early morning synoptic compilation gives a good view of how local weather developed during the course of the week. On Monday, the remnants of the previous continental high was still lingering over the eastern half of southern Africa. This quickly departed to the east and early summer conditions resumed. In the wake of the departing high and amplified by the so-called heat-low that always forms over the central ground of the sub-continent, a weak trough developed, as usual, from Angola through...

Map: 12-hour precipitation forecast for Sunday 01 October 2017. The map indicates expected conditions for the 12-hour period preceding the date at the bottom of the map. Source GrADS/COLA, George Mason University. As the season passes the equinox, the sunshine hours per day exceeds the 50/50 split meaning the period of energy infusion is longer than energy depletion. In short, the southern hemisphere slowly gets warmer as it receives more energy during the day than what it radiates at night. Of course, the weather is not so simple. The sun’s angle also changes every day and the amount of...

Map: Accummulated precipitation forecast for the nine days from Friday 22 September to Saturday 30 September. Source. GrADS/COLA, George Mason University. Except for the southern-most strip of the Karas Region along the Orange River, the whole country continued to be under high pressure control in the upper air. The clouds that appeared from Lüderitz to Ariamsvlei on Thursday and Friday formed the northern limit of a very wide convergence zone running from the Western Cape to the Orange River Valley. For the duration of the week, the weather followed a regular transition pattern except for the persistent and widespread...

Map: Accummulated precipitation forecast for the nine days from Friday 15 September to Saturday 23 September. Source. GrADS/COLA, George Mason University. Two prominent features stand out in this week’s weather development. The first is the almost total collapse of the southern Indian high pressure cell and the second is the powerful anti-cyclonic alto circulation over the sub-continent. The cut-off low that developed last week ahead of the South Atlantic high pressure cell did not dissipate as easily as expected. It did not move into the southern seas either but remained more or less on the same longtitudinal track on...

Map: Sea Level Pressure on Saturday 09 September and the height of the 500 mB surface indicated by the coloured areas. The forecast map is relevant to the 12-hour period preceding the date at the bottom. Source: GrADS/COLA. The surface pressure map, although based on data collected 48 hours ealier and relevant only to Saturday, offers a good interpretational framework to understand what transpired during the week. The week started with a typical late winter stance. The South Atlantic high pressure cell lay some distance offshore the west coast while the southern Indian high sat just south-east of Madagascar....

Map: Mean Surface Temperature Anomalies for Southern Africa from 01 Sept to 09 Sept 2017. Source: Temperature Forecasts from the National Centers for Environmental Prediction. GrAds/COLA. This was another week where the two high pressure cells on either side of the sub-continent failed to have a significant impact on land while the low pressure system south of Cape Agulhas, and between the two highs, had a much bigger impact to the north. Since the low pressure system developed behind the trailing rim of the southern Indian high, it was characterised by a pronounced north to south airflow, leading to...

Graph: El Nino Southern Oscillation forecast ensemble to May 2018 Source: Update as at 21 August 2017 prepared by:NOAA, Climate Prediction Center / NCEP Over the past two weeks, the sea surface temperatures in the eastern and central Pacific have moved into a well-defined La Nina stance. This has prompted the Climate Prediction Centre in the USA, in their latest update to forecast below-average Pacific temperatures up to May next year. Lower temperatures in the Pacific have in the past always translated into above-average rainfall for Namibia. The Pacific stance is corroborated by the 30-day Moving Southern Oscilation Index...