MAURITIUS METEOROLOGICAL SERVICES

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1 MAURITIUS METEOROLOGICAL SERVICES CLIMATE JUNE 2018 Introduction The first half of June 2018 was warmer than usual with the day time maximum of more than 2 C lingering over most regions over Mauritius. However by the end of the month, the typical June weather systems, that is the Mascerenes High, began to influence the region. It brought cooler air as well as a strengthening in the wind regime over our region, thus putting an end to the warm spell. Since the end of summer and start of winter in Mauritius, neutral condition of both ENSO and Indian Ocean Dipole (IOD) persisted. 1. Rainfall Fig. 1: (a) Observed rainfall (b) rainfall anomaly (mm) Fig. 2: Regional rainfall distribution (based on 23 stations) June 2018 rainfall was normal over the island. Perturbation in the trades contributed to most of the rainfall, though occasionally afternoon convective cloud built-up brought some localised showers. Most regions had normal rainfall except to the Southeast and overthe Central Plateau where deficient rainfall between mm was observed. Rainfall in excess of up to 70 mm was recorded in some localities to the south.. The highest 24 hour-rainfall recorded was 73 mm at Pradier on the 21

2 Surface Temperature (a) Perturbed weather on 04 (b) Perturbed weather on 21 Fig 3: Weather systems during June 2018 (c) Perturbed weather on Surface Temperature June 2018 is amongst the fifth warmest June on record since 1969 (based on temperature recorded at Plaisance) Fig. 4: Maximum temperature trend for June from

3 There were two well marked warm spells during the first three weeks of June 2018 (Fig 7). The first warm spell was during the first week with most stations recording temperature anomalies of more than 2 C (Fig 6(b)). There were records of the day maximum temperature by more than 3 C for three consecutive days from the 05 to 08 in the region of Belle Mare, Mon Desert Alma, Arnaud, Bois Cheri and Mon Desert Mon Tresor. Moreover, new records of the extreme maximum temperature were set up during that period, on the 5 at Reduit 30.5 C (previous 29.0 C), on the 7 at Mon Desert Mon Tresor 30.5 C and at Gros Cailloux 29.3 C (both previously 28.5 C. The second warm spell prevailed between the 17 to 20 with again most places recording day maximum anomaly of more than 2 C. Also, new records of the extreme maximum temperature were set up, on the 18 at Port Louis 31.9 C (previously 31.8 C) and on the 20 at Domaine Les Pailles 31.9 C (previously 31.3 C). The number of cold days for the winter month of June 2018 was less than 5 days in most regions. On the other hand, at Providence and Mon Desert Alma during more than half of the month warm conditions prevailed. Similar ly the night-time temperatures recorded at most places during the first warm spell had an anomalies of more than 2 to 4 C (Fig 6(a)). These observation showed a dominantly warmer air mass than the typical June weather pattern. During the second warm spell the minimum temperature occasionally plummeted to values below the seasonal mean, mostly due to clear sky and calm wind conditions. The warm day time temperatures during this second spell was mostly due to above average daily as shown in Fig. 10. The number of cold nights were less than 5 days in most places. (a) Eventually, with influx of cold air by the end of the month, both the maximum and minimum temperature dropped. This led to new records of the extreme minimum temperature, notably on the 28 at Mon Loisir Sugar Estate 15.6 C (previously 17.7 C) and on the 29 at Bagatelle 13.3 C (previously 15.2 C). (a) Fig. 5: (a) Maximum (b) Minimum temperature distribution

4 Some stations had up to 17 warm days (maximum temperature anomaly (anomax) >2 C). Stations Highest anomax ( C) Number of warm days. Alma Arnaud Belle Mare Bois Cheri D Les Pailles M Desert Alma M. D. MTresor ML Roullard Mon Bois Port Louis Providence Quatre BOrnes Riche En Eau Sauveterre U. Park MSIRI (a) Fig. 6: (a) Maximum (b) Minimum temperature anomaly (b) Fig. 7: Daily maximum temperature anomalies at Vacoas and Plaisance Fig. 8: Daily minimum temperature anomalies at Vacoas and Plaisance

5 3. Sunshine and Humidity 4. Winds Fig. 9: Daily Relative Humidity: Vacoas (blue) and Plaisance (red) Fig. 10: Daily sunshine hours: Vacoas (blue) and Plaisance (red) Overall for June 2018, the mean monthly relative humidity was close to the mean at Vacoas and slightly below at Plaisance as shown in Fig 9. During the first warm spell, the relative humidity was near the long term mean whereas during the third week for the second warm spell, the relative humidity was below at Plaisance and slightly below at Vacoas.By the end of the month a gradual drop in relative humidity was noted both at Vacoas and Plaisance to a change in air mass over the island. Daily mean sunshine hours were slightly below by 0.3 hours at Vacoas (6.9 hours) and at Plaisance, it was slightly below by 0.2 hours (5.6 hours). Cloud cover during the rainy episode led to nil sunshine hours for the period 25 to 26. This is in concurrence to the drop in maximum temperatures shown in Fig. 7 and Fig Winds The trade winds, a wind regime from the South East wind is the striking feature taking into consideration the wind distribution at Plaisance (Fig. 11). However it must be noted that for a winter month, it was quite abnormal to observe the frequency of winds from north-westward to north-eastward. These northerly winds were an indication of a warm air mass, originating equatorward, which influenced our region. Fig. 11: Wind frequency at Plaisance

6 5. Sea Fig. 13: Waveheight distribution in the region of Blue Bay Fig 13 shows that 60% of the wave height recorded were on average 2m to 3m and 30% of the events were 3m to 4m. On rare occasions, wave heights of the order of 4m to 5m.were recorded Fig. 12: Waverose in the region of Blue Bay The state of the sea was dominated by waves from mainly the south, indicating the influence of the anticyclone, Fig 12. On several occasions, south westerly swells affect the state of the sea causing an increase in the wave-height. The sea surface temperature was near 25.9 C at the start of the month and slowly decrease to reach 24.8 C by the end of the month Fig 14. The two warm spells contributed to increase the SST between the 7 to 10 and more significantly between 16 to 21. There decrease in the SST was more pronounced by nearly 1 C from 21 to 26. The right of publication in print, electronic and any other form is reserved by the Meteorological Services. Any part of this document may be reproduced provided complete source is acknowledged or after authorization from: Director, Meteorological Services, St Paul; Road Vacoas, Tel: /32, Fax: , meteo@intnet.mu Fig. 14: Sea surface temperature in the region of Blue Bay