Bulletin de la Météo.

Un hiver au dessus de la normale

L’hiver 2019 sera un peu plus chaud de la normale de la saisnon selon la station météo de Vacoas avec temperature qui pourrait descendre jusqu’à 12 degrés dans les hauteurs en cas de ciel clair pendant les mois de Juillet à Septembre.

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

nference 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

SOurce: MMS

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