[Vidéo News] Présentation du Winter 2024 Outlook

Seasonal Outlook for Winter 2024

1.0 Introduction

he Winter 2024 Seasonal Outlook gives an insight of the expected evolution of the climate during the winter months in Mauritius and Rodrigues. The content of this outlook is meant to be used as general guidance for planning purposes by stakeholders in various socio-economic sectors.

2.0 Background

In general, a seasonal forecast provides information on how likely the state of the climate in coming season, whether it will be wetter, drier, warmer, or colder than normal.  It is not an attempt to forecast the detailed day-to-day evolution of weather.

The winter season in Mauritius and Rodrigues occurs from May to October. The weather during Winter is often characterised by persistent trade winds emanating from anticyclones transiting from west to the east in the Southern Indian Ocean. Temperatures are cooler, especially during the months of June to September. May and October are generally considered as transition months.

The key factors used to generate the most likely scenario for the winter are the behaviour of meteorological and oceanic parameters such as El Niño Southern Oscillation (ENSO) and the behaviour during analogue years. In addition, other global, regional, and local predictors are analysed in the process of the preparation of this outlook.

3.0 Conclusions

Based on analysis of linear regression models of the meteorological and oceanic parameters that drive our climate in the southwest Indian Ocean and climate forecast from various model products from Global Producers of Long-Range Forecast, the most likely outlook for winter 2024 is as follows:

1. Observed trends of meteorological parameters in the region indicate that the onset of Winter 2024 will be during the first fortnight of May.
2. Winter 2024 rainfall over Mauritius is expected to be normal. Initially rainfall will be close to normal and is expected to be slightly below by the end of winter. The cumulative rainfall will be around 600 mm which represent 90% of the Long Term Mean. Most of the rains will be concentrated mainly over the Central Plateau, to the East and the South.
3. Rainfall over Rodrigues is expected to be below normal. The cumulative rainfall for Winter 2024 will  be around 290 mm which represent 70% of  the Long Term Mean.
4. The day mean maximum and night mean minimum temperature will be close to the normal. In Mauritius, temperature during the day will be around 23 degrees Celsius over the central plateau and 28 degrees Celsius along the coastal regions. The night temperature will be around 16 degrees Celsius over the central plateau and will be around 19 degrees Celsius along coastal regions.
5. In Rodrigues, temperature during the day will be around 24 degrees Celsius over the high grounds and 27 degrees Celsius along the coastal regions. The night temperature will be around 16 degrees Celsius over the high grounds and will be around 20 degrees Celsius along coastal regions.

However, due to intra-seasonal variations, on certain occasions when the Mascarenes will be under the influence of strong anticyclones, the Islands may experience day temperatures below normal by 2 degrees Celsius or more.

On few occasions, especially due to clear sky and calm wind conditions at night, it is likely that the minimum temperature may drop to 9 degrees Celsius in certain places in Mauritius. Over Rodrigues, minimum temperature may drop to 13 degrees Celsius over the high grounds. Table 1 and Table 2 show the forecast of monthly average maximum and average minimum temperatures over different regions in Mauritius and Rodrigues respectively.

Table 1: Expected monthly average maximum and average minimum temperatures (in degrees Celsius) over Mauritius.

Table 2: Expected monthly average maximum and average minimum temperatures (in degrees Celsius) over Rodrigues.

1. Inference to other parameters
   1. Wind will blow mainly from the East South East with an average speed varying between 25 and 35 km/h. During the peak winter months mainly in July and August, the passage of strong anticyclones to the south of the Indian Ocean may cause strong pressure gradient over the Mascarenes, resulting in wind gusts that may peak to above 90 km/h in the exposed areas;
   2. On certain occasions, the sea will become very rough with heavy swells generated by the combined effect of travelling extratropical deep lows and strong anticyclones to the south of the Mascarenes. The breaking waves are likely to reach the western, southern and eastern shores of Mauritius and Rodrigues and may at times cause tidal surge leading to temporary inundation of low-lying coastal areas; and
   3. The Sixth Assessment Report from Intergovernmental Panel on Climate Change (IPCC AR6 WGI) states the following: it is an “established fact” that human-caused greenhouse gas emissions have “led to an increased frequency and/or intensity of some weather and climate extremes since pre-industrial times”. In this regard, extreme weather events including moderate to heavy showers, significant variation in temperatures and strong wind conditions are very likely to occur over Mauritius and Rodrigues during winter 2024.

This report will be updated upon availability of fresh information.