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Seasonal Climate Forecast

 

 

MAURITIUS METEOROLOGICAL SERVICES

 

Winter 2019 - Seasonal Outlook

 

1.0 Introduction

 

The Winter 2019 Seasonal Outlook prepared by the Mauritius Meteorological Services, gives an insight of the expected evolution of the climate during the winter months in the Republic of Mauritius. The contents of this outlook are meant to be used as general guidelines for planning purposes by stakeholders in various socio-economic sectors.  Winter starts around mid-May and ends in 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 is often characterized by persistent trade winds emanating from anticyclones in the South Indian Ocean. Temperatures are cooler, especially during the months of June to September. May and October are usually known as transition months with alternate relatively warm and cold episodes.

The behaviour of various meteorological parameters in analogue years as well as El Nino Southern Oscillation (ENSO) and sea surface temperature in the Indian Ocean are analysed to generate objective scenarios for the winter months. Global, regional and local predictors are analyzed during the preparation of this outlook.

 

3.0 The Past Summer

A weak El Nino prevail over the central equatorial Pacific Ocean during last summer, though in the months of January and February 2019, sea surface temperature was near neutral ENSO conditions.

Cumulative summer rainfall over Mauritius was close to the seasonal mean with 1433 mm, representing 108% of the normal. The rainfall, however, was not evenly distributed both spatially and temporally.

The mean summer temperature was slightly above the seasonal mean. The highest departure from the long term mean was recorded during the month of January 2019 (+2odeg Celsius). Extreme maximum of 36.3oC was recorded at Riviere Noire and followed by 35.4oC at Choisy Estate in January.

Summer 2018-2019 had an abnormally high cyclonic activity with 15 tropical storm/cyclone formations, equal to the 1993-1994 cyclone season. Out of the 15 formations 10 reached the intense tropical cyclone stage which is an all-time record.

 

4.0 Conclusions - Outlook for winter 2019

Based on both linear regression models and probabilistic climate forecast from various climate models, the most likely outcome for Winter 2019 is as follows:

(1) Wintry type weather is gradually setting in as from the first fortnight of May 2019.

(2) Cumulative rainfall over Mauritius is likely to be near normal to slightly above normal with a mean amount of about 700 mm. Slightly wetter conditions may prevail from May to July.  Rainfall is likely to be slightly below normal in September and October. The rainy periods will be mainly concentrated over the Central Plateau, to the East and the South.

Normal rainfall is expected over Rodrigues with a mean of 350 mm over the island.

(3) Day temperature is likely to be close to the seasonal mean, both at Mauritius and Rodrigues. Night temperature will be slightly above normal. The mean temperature (mean of maximum and minimum) will be slightly above normal over both islands.   

However, there will be intra-seasonal variation, when on certain occasions the Mascarenes will be under the influence of strong anticyclones and the Islands may experience relatively cold surge resulting in slightly below normal day temperature during that period

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 12 degrees Celsius especially during the months of July to September.

At Rodrigues, minimum temperature may drop to near 14 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 (Pointe Canon).

 

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

EAST

27

20

26

19

24

18

24

18

26

18

27

19

WEST

29

20

27

19

26

17

27

17

28

18

29

19

NORTH

29

19

27

19

26

17

26

17

27

18

28

19

SOUTH

27

21

26

20

25

19

25

18

26

19

27

20

CENTRE

25

19

24

18

23

16

23

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

29

23

28

23

27

22

26

21

26

21

27

21

Plaine Corail

29

24

28

24

27

23

26

22

26

22

27

22

 

 

 

 

 

 

 

 

(4) Inference to other winter weather

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 80-90 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 cause temporary inundation of low-lying areas at times, especially in the southern and western sectors.

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.

 

Meteorological Services

St Paul Road, Vacoas

Date: 10 May 2019