Seasonal Climate Forecast

Winter 2020 - Seasonal Outlook

 

1.0 Introduction

The Winter 2020 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 guidelines for planning purposes by stakeholders in various socio-economic sectors. Winter in Mauritius and Rodrigues has been defined as the period from May to October.

 

2.0 Background

A seasonal climate forecast aims to estimate the change in the likelihood of a climatic event happening in the coming months. A seasonal forecast can provide information on how likely it is that the coming season will be wetter, drier, warmer or colder than normal. A seasonal climate forecast is not an attempt to forecast the detailed day-to-day evolution of weather.

Winter weather in Mauritius is often characterized 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) and analogue years are the key factors used to generate the most likely scenario for the winter months. Global, regional and local predictors are analyzed in the process of the preparation of this outlook.

 

3.0 The Past Summer

During summer 2019-2020, neutral ENSO persisted in the Pacific Ocean. The Indian Ocean Dipole was positive till December 2019 and migrated towards neutral conditions as from January 2020.

Onset of summer rainfall was on time. With the exception of February whereby cumulative rainfall was below the monthly mean, the rest of the summer months received normal to slightly above normal rainfall. Consequently, accumulated rainfall for Summer 2019-2020 resulted in slightly above long term mean rainfall.

The mean temperature was above average during the first half of summer and close to normal during the second half of summer.

The cyclone season 2019-2020 was slightly late with the first formation occurring in the first week of December 2019. In all 10 tropical storms were named during the season; of which 1 became very intense tropical cyclone, 2 intense tropical cyclones, 3 tropical cyclones, 1 severe tropical storm and 3 moderate tropical storms.

4.0 Conclusions - Outlook for winter 2020

 

Wintry type weather has been observed as from the second week of April. Based on both linear regression models and probabilistic climate forecast from various climate models, the most likely outcome for winter 2020 is as follows:

 

(i) Observed trends of meteorological parameters in the region indicate that the onset of winter will be earlier and will settle down as from the end of April 2020.

(ii) Rainfall over Mauritius is likely to be near normal during the first half of the season and slightly below normal for the second half. The cumulative rainfall is expected to be around 600 mm. The rainfall will be concentrated mainly over the Central Plateau, to the East and the South.

Normal rainfall is expected over Rodrigues with a mean of 400 mm over the island.

(iii) Day maximum temperature will be close to the normal during first half of winter and slightly above normal during the second half both at Mauritius and Rodrigues. Night temperature is expected to be slightly above normal.

However, there will be intra-seasonal variation, when on certain occasions the Mascarenes will be under the influence of strong anticyclones and the Islands are likely to experience relatively cooler surge resulting in below normal temperature.

On a few rare occasions, especially due to clear sky and calm wind condition, it is likely that the minimum temperature at Mauritius may drop to near 10 degrees Celsius.

At Rodrigues, minimum temperature may drop to near 13 degrees Celsius over the high grounds.

Table 1 below shows the forecast monthly average maximum and minimum temperatures in degrees Celsius for the different region of Mauritius and Table 2 gives the expected maximum and minimum temperature for Rodrigues.

Table 1: Expected monthly average maximum and minimum temperatures over Mauritius.

	May		Jun		Jul		Aug		Sept		Oct
	Max	Min	Max	Min	Max	Min	Max	Min	Max	Min	Max	Min
WEST	29	20	27	19	26	17	26	17	28	18	29	19
NORTH	29	19	27	19	26	17	26	17	28	18	29	19
EAST	27	20	26	19	24	18	24	18	26	18	27	19
SOUTH	27	21	26	20	25	19	25	18	26	19	27	20
CENTRE	25	19	24	17	22	16	22	16	24	17	25	17

 

 

Table 2: Expected monthly average maximum and minimum temperatures over Rodrigues.

	May		Jun		Jul		Aug		Sept		Oct
	Max	Min	Max	Min	Max	Min	Max	Min	Max	Min	Max	Min
Pte-Canon	28	23	27	22	26	21	26	21	27	21	28	22
Plaine Corail	28	23	27	22	26	21	27	21	28	22	29	22

 

(iv) Inference to other parameters 

a) It is likely that the trade wind, mainly from the East South East, will blow at an average speed of 25 to 35 km/h.

Occasionally, particularly during the peak winter months i.e. 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 to reach 90 km/h in the exposed areas.

b) On some occasions, the sea is likely to become very rough with heavy swells generated by the combined effect of deep travelling lows and strong anticyclones to the south of the Mascarenes. The breaking waves are likely to reach the southern and western shores of Mauritius and Rodrigues and may at times cause temporary inundation of low-lying areas.

c) In line with the findings of IPCC Fifth Assessment Report and the Special Report on Global Warming of 1.5^oC (SR15), extreme weather events including short duration high intensity rainfall, large variation in temperatures and windy conditions are very likely to occur occasionally over Mauritius and Rodrigues.

This report will be updated upon availability of fresh information.

 

 

Mauritius Meteorological Services

St Paul Road, Vacoas

Date: 30 April 2020