The Weather Guru, Garth Sampson, has recently emailed me some interesting articles on this flood. Even though I have previously written a blog on it, it was based upon my personal experiences and as well as that of my family instead of being a generic article about rainfall and general human interest elements. Amongst these articles was one written by JP Viviers of the SA Weather Bureau on which this blog is largely based. Instead of a wholly human-interest story, it is largely explains the meteorological aspects as well as some statistics combined with some unusual interesting consequences.

Main picture: Water flowing over Beach Road at Happy Valley

The guilty weather phenomenon
I have always been intrigued about why Port Elizabeth periodically experiences severe flooding but have never taken the time to investigate it. In his article entitled ‘n Terugblik op die groot vloed in Port Elizabeth, 1 September 1968, JP Viviers explains it as follows:

Synoptical maps of the previous day (31 August 1968) over the Port Elizabeth region gave no clear indication of the possibility of imminent heavy rainfall. However, there were some indications of a cut-off layer building in the upper air along the West Coast, and the presence of a shallow surface layer approximately 300km north-west of Cape Town.

So we have the culprit: Cut-Off Lows. If this phenomenon has played such a huge part in the life of the city, why aren’t all Port Elizabethians aware of its existence?

So what is a Cut-off Low? Apparently there are a number of weather systems prevalent in South Africa of which this is one. According to the article ‘Cut-off Lows’ a common occurrence in SA weather’ on the internet, this weather system is “It is defined by how it forms. The air in the mid-levels of the atmosphere over South Africa generally flows from west to east. When this flow is disturbed, a trough forms (in a similar way that a river meanders). The trough can then intensify and develop into a low-pressure system. If this low-pressure system gets “cut off” from the basic westerly flow, then a cut-off low has been born. If they are intense enough, Cut-off Lows invariably result in heavy rains in various parts of South Africa. However, the western and southern parts of the country appear to bear most of the brunt of the torrential rains. While Cut-off Lows are a common occurrence in South Africa, and have been observed predominantly between March and May, and from September to November, once in a while an unseasonal event hits our shores.

How severe was the downpour?
Between 07:40 and 12:00, no less than 352 mm deposited on the town. It was also the day on which the most rainfall had fallen in a 24-hour period from 1951 namely 429 mm. The total rainfall for that month was 468 mm. This total was 700% of the normal rainfall for September was the highest figure since 1926 in the vicinity of the airport. According to an automated rain gauge of the municipality in 24 hours recorded about 552 mm at the municipal reservoir in Brunswick Road, Adcockvale.

A total of 26,000,000 tons of water was dumped on Port Elizabeth.

Consequences
Of the consequences, the most distressing is the loss of life. According to Viviers, “nine people perished, eight of whom were drowned. The ninth person was electrocuted at his house in Central, when he attempted to fix a leak in his house’s roof.”

Substantial damages were caused. They amounted to almost R604m (R40m in 1968).

Unknown is the quantum of the loss of animals. One such loss that Viviers mentions is that of the Snake Park. More than one hundred snakes which were housed in an open-air pen were either drowned or died of cold when the heaters in the pen malfunctioned.

Many people were compelled to take refuge on the roofs of houses and other buildings. In some areas, the houses were more than window-high under water. In a flash, streets were transformed into bustling rivers and old tributaries that had been built over years ago, were washed open. The airport was soon unusable with water a foot deep over the runways.   Communication with the airport was disrupted and electronic equipment of the weather bureau was out of operation. As a consequence, no airline departures could be made in the afternoon.

At the time of the flood Port Elizabeth had three ambulance depots. The main depot was in Albany Road, with two smaller depots in Walmer and Sidwell. The main depot was soon cut off when the main road to Albany Road was washed away! The main fire service offices which were also stationed in Albany Road was also isolated.

There was also a lighter side of the disaster. A motorist driving in First Avenue, Newton Park, during his lunchtime was surprised when a man in a canoe paddled past him. Many fish, some weighing up to 3 kg, were washed out of the North End Lake and caught in the main street with one’s bare hands.  Goldfish were also flushed out of the goldfish pool at St. George’s Park. They found a temporary home in a pool of water under the main pavilion of Crusaders Rugby Ground.

Weather Bureau’s prognostications for September 1^st
My assumption is that as the Weather Bureau was aware of this phenomenon and assuming that they possessed the tools to detect it, then the possibility of severe rainfall should have been present in their forecasts.

 Viviers continues with the cause of the flood: Simultaneously a strong high-pressure system pushed in from the south behind a cold front trough approaching Marion Island from the west. A weak trough was present over the inland parts of the Cape Province and southern Free State associated with a cold front spanning from Pofadder in the Northern Cape in the direction of Port Elizabeth.

Port Elizabeth’s upper atmosphere also indicated a cooling off in comparison with the previous day. Southeast of Durban there was a trough with a cut-off layer about 900 km north-north-east of Marion Island. Notwithstanding the presence of the low-pressure layer along the west coast, the three-hourly pressure readings 14:00 SAST over the western parts of the country, there was no strengthening or movement of the low was indicated and in fact they were even relatively slightly rising over Southwest Cape. In this situation, it could have been predicted that the west coast layer was likely to move over the Cape interior especially with a view to the existing interior trough. Thus, colder weather with rain could be expected over large parts of the Cape Province. Heavy snowfalls, however, would not normally be predicted because there were no signs of descent of the layer and because the air over the interior was not particularly humid. Furthermore, at that stage it was not known how strong the high pressure would intensify south of the country.

So what were the actual weather bulletins?
31 August 1968: Humid air is present over the eastern portion of the country where showers and thunder storms will occur.

The low near Cape Town will result in rain across the Western and Southern Cape.

1 September 1968
A deep low-pressure system is prevalent across the eastern cape causing general rain across the Eastern and Southern Cape while intermittent showers or thunderstorms will be experienced over the O.F.S., Natal and Transvaal. It will become cooler over the northeastern areas.

If there was a mea culpa, this would be it. It is clear that the situation was underestimated. It is very likely that that such an incident will not occur again with the present forecasting models, satellite imagery and the knowledge now available to the forecasters.

Sources
‘n Terugblik op die groot vloed in Port Elizabeth, 1 September 1968 by JP Viviers from the Weerburo Nuusbrief September 1993
‘Cut-off Lows’ a common occurrence in SA weather https://www.enca.com/weather/cut-lows-common-occurrance-sa-weather
Thanks to Garth Sampson for supplying me with weather related articles
The translation is largely mine with some assistance from Johan Grobler