Seasonal Climate Forecast

MAURITIUS METEOROLOGICAL SERVICES
Seasonal Outlook for Winter 2025

1.0 Introduction
The Winter 2025 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
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 the South Indian Ocean from
west to east. Temperatures are cooler, especially during the months of June to September. May and October are generally considered as transition months. The behavior of meteorological and oceanic parameters such as El Nino Southern Oscillation (ENSO), Indian Ocean Dipole (IOD) and the behaviour of meteorological and oceanic parameters in analogous years are the key factors used to generate the most likely scenario for the season. Global, regional and local predictors are analysed in the process of the preparation of this outlook.

3.0 The Past Summer 2024-2025
Weak La Nina conditions prevailed mostly throughout Summer 2024-2025, transiting to neutral ENSO condition by the first week of April 2025. A neutral Indian Ocean Dipole was observed in the Equatorial Indian Ocean for Summer 2024-2025.

Summer 2024-2025 began with a very wet November that was ranked as the seventh wettest November over the last 30 years with 174% of Long-Term Mean (LTM) 1991-2020. December 2024 recorded slightly below normal rainfall with 82% of the LTM. Over the last 25 years, January 2025 was the second driest January with only 30% of the LTM and February 2025 ranked as the sixth driest February with 59% of LTM. The onset of summer rain delayed and it occurred by the end of February 2025. March 2025 was the seventh driest March since the last 30 years with 57 % of the LTM. It is to be noted that April 2025 had 122% of the LTM. The cumulative rainfall for last summer (November 2024 to April 2025) was below normal with 958 mm (71% of the LTM). The mean temperature was slightly above normal during the summer months. The highest maximum temperature recorded was 34.2 degrees Celsius at Le Morne on 21 February 2025. The cyclone season 2024-2025 started early and the first storm was named in the first week of October 2024
in the South-West Indian Ocean cyclone basin. It is to be noted that there were fourteen named storms over our basin, which is above the mean (10 on average). These include Taliah, Vince and Courtney which were named by the Bureau of Meteorology in the Australian area of responsibility and later moved in the South West Indian Ocean. Out of these fourteen named systems, two reached very intense tropical cyclones, four intense tropical cyclone, three tropical cyclones, one severe tropical storm, two moderate tropical storms and two were subtropical storms. Intense tropical cyclone Bheki warranted the issuance of a cyclone warning Class IV at Rodrigues and then a cyclone warning Class I for Mauritius. The Intense Tropical Cyclone Chido directly hit Agalega with cyclonic winds, devastating most of its infrastructure. Moderate tropical storm Faida warranted an issuance of a cyclone warning class II at Rodrigues and cyclone warning class I for Mauritius. A cyclone warning class III was issued for Mauritius during the passage of Intense tropical cyclone Garance near the island.

4.0 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 2025 is as follows:
i. Observed trends of meteorological parameters in the region indicate that the onset of Winter 2025 will be timely by mid-May 2025.
ii. Winter 2025 rainfall over Mauritius is expected to be near normal with a cumulative rainfall of around 600 mm, representing 90 % of the LTM. Most of the rains will be concentrated mainly over the Central Plateau, to the East and the South.
iii. The cumulative rainfall for winter 2025 for Rodrigues is expected to be near normal with around 490 mm, representing 90% of the LTM.
iv. The day mean maximum and night mean minimum temperature will be slightly above normal in Mauritius, temperature during the day will be around 24 degrees Celsius over the central plateau and 29 degrees Celsius along the coastal regions. The night temperature will be around 17 degrees Celsius over the central plateau and will be around 19 degrees Celsius along coastal regions.
v. In Rodrigues, temperature during the day will be around 25 degrees Celsius over the high grounds and 28 degrees Celsius along the coastal regions. The night temperature will be around 18 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 condition 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.
vi. Inference to other parameters

   a. Wind will blow mainly from the East South East at a 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 exceed 90 km/h in the exposed areas;

   b. 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   high        energy waves are likely to reach the southern and western shores of Mauritius and Rodrigues and may at times cause tidal surge leading to temporary inundation of low-lying coastal areas; and
   c. Published by the World Meteorological Organisation (WMO) in March 2025, The State of the Global Climate 2024 provides “clear signs of human-induced climate change reached new heights in 2024, which was likely the first calendar year to be more than 1.5°C above the pre- industrial era, with a global mean near-surface temperature of 1.55 ± 0.13 °C above the 1850- 1900 average”. It further underlines “the massive economic and social upheavals from extreme weather and the long-term impacts of record ocean heat and sea-level rise”. This alarming milestone underscores how the changing climate is fueling a surge in extreme weather events. Additionally, the rising sea levels are increasingly threatening densely populated coastal areas with flooding and wave damage. In this context, Mauritius and Rodrigues are also likely to experience extremes weather events during Winter 2025 that include moderate to heavy rainfall episodes, significant temperature variations, strong winds and heavy swells.

This report will be updated upon availability of fresh information.

Mauritius Meteorological Services
St Paul Road,
Vacoas
Date: 23 May 2025