One On One

Q & A – SA Weather Service Rejoyce Mohlamme

The world continues to experience rapidly changing weather patterns and last week, warnings were issued that parts of southern Africa would be hit by yet another tropical cyclone, just about a month since Cyclone Idai ravaged parts of Mozambique, Malawi and Zimbabwe. Tropical cyclones, which are fast rotating storm systems with low-pressure centres accompanied by strong winds and a spiral arrangement of thunderstorms that produce heavy rains, claimed thousands of lives in the region and destroyed billions on rands in infrastructure. The Weekly’s Martin Makoni spoke to SA Weather Service forecaster Rejoyce Mohlamme about the changing weather patterns, the causes and how they could affect the future. Excerpts:

The southern African region has been experiencing extreme weather conditions in the form of heatwaves and heavy rains in recent years, what could be the reason for that?

Climate change is expected to affect or alter the frequency and also the severity of extreme weather conditions, however, it is very challenging to link or view short-term weather event in an ‘eye’ of climate change. Some of the reasons being that climate is mainly a hindsight of long-term data analysis of about 30 years at minimum. For example, when climatologists talk about global warming, it is a comparison of current temperatures to the averages of the past decade. Moreover, in a short-term, we also experience the so called ‘record’ weather phenomenon when one or two short-term occurrences way exceed averages. Change in weather pattern is broad it can be researched at a bigger scale using a lot of historical data. Do one or two swallows declare summer? That’s the challenge.

Several countries in the region, including South Africa have been experiencing floods, does that mean more rains are being received now than in the past? 

Well, a simple comparison of current rainfall figures with climate data for the central and eastern Free State since February 2019 up to now have come above normal; which could be attributed to two well developed rain producing weather systems during that period. On the other hand, early summer and mid-summer rainfall comparison came way below normal, and this has been the trend for the past five years or so over the areas dependent to summer rainfall, which therefore take us back the debate of climate change. Furthermore, the western half of South Africa was so dry that dams went empty.

There are reports that another strong tropical storm is heading for the south-east coast of Africa, can you explain what happens in such a situation?

A tropical cyclone is a rapidly rotating storm system characterised by a low-pressure center, a closed low-level atmospheric circulation, strong winds, and a spiral arrangement of thunderstorms that produce heavy rain. As we speak, Tropical cyclone Kenneth is expected to hit northern Mozambique as well as southern Malawi.  

Tropical cyclone Idai recently hit the same region, is it normal for such a weather phenomenon to occur at such a frequency, what will be happening in the weather system?

To be frank, the frequency is becoming a concern given that people are just starting to pick-up the pieces from the previous event. It’s very difficult.

How strong is Tropical Storm Kenneth likely to be in terms of wind speeds and the amount of rains it is likely to bring? 

The weather office responsible for forecasting and monitoring Tropical cyclone in our region is La Reunion. Therefore, Tropical cyclone is expected to make landfall on the 25th of April 2019 in the afternoon at Cabo Delgado on the northern Mozambique coast. The Tropical cyclone Kenneth is bringing heavy rains, above 100 mm per day, and hurricane winds, over 215 km/h to western Comoros, northeast of Mozambique and the extreme southeast of Tanzania. Kenneth will also be associated with a storm surge of one to three meter sea level rise and very high seas waves above nine meters m along the coast. On Friday, Tropical Cyclone Kenneth will become an overland depression bringing heavy rains and storm winds to the northeast of Mozambique and the extreme southeast of Tanzania.

Why is Mozambique now in the path of these extreme tropical storms, in the past, it was part of Madagascar experiencing them, what has changed?

Not really, what happens is that storms will weakens as they enter Madagascar due to unfavourable inland conditions and sometimes die before existing. But if they survive the inland conditions of Madagascar, of which they do at times, storms will pick-up or re-gain strength in the sea. That was the case with Cyclone Elena in 2000… Moreover, there are few number of storms that occurred this year in the southern hemisphere but we do not hear about them because they were not intense enough and/or deviate southwards and become tropical depressions towards Durban.

Overall, what sort of weather conditions is the region likely to experience over the winter period? 

The seasonal weather forecast has indicated mostly below normal rainfall in the summer rainfall areas but normal to above normal rainfall over winter rainfall areas of the south-western half of the country, which means a number of frontal systems moving through.

How are these tropical storms named, they all seem to have people’s names?

In our region tropical low pressure systems receive names as soon as they reach the moderate tropical storm stage meaning when the average wind exceeds 33 knots every 10min. The names are chosen on pre-defined alphabetical lists. Until the 1999-2000 season, they were previously named after females due to destructions they cause BUT women protested this culture and therefore are also named after man. The is a team dedicated on naming storms around the world. I do not know exactly the procedures. Here is food for thought; the destruction comparison of storms named after man to those named after women. According to La Reunion since the 2000-2001 season, the first names on the lists include first names from the different member countries of the South West Indian Ocean Cyclone Committee (which includes 15 member countries, the majority from southern Africa), being chosen consensually at the Tropical Cyclones Committee (which is usually held every two years) and this balancing the first names from different countries. Currently the storm that are active in our region is Kenneth and Lorna.