The Climate Over Sri Lanka up to the Yala 2015

By: Prabodha Agalawatte, Udara Rathnayake, Zeenas Yahiya, Lareef Zubair

Summary

The rainfall from January to March leading up to the 2015 Yala season was slightly lower than normal; the rain picked up in April and May exceeding normal values. Even though the rainfall remained below normal for the rest of the season through August, the water availability was suited for irrigated cultivation such as for rice. North-central region of the country mostly received above average rainfall while south western regions which usually receive high rainfall mostly received below average rainfall. During September the entire country received above average rainfall. Heavy rainfall was observed during last two weeks of September which caused floods in several areas of the country. An El Nino event which had developed to a borderline state for many months became a fully-fledged event by July 2015. Usually during an El Nino, the rainfall is deficient from January to March and June to August. Rainfall in October to December is above normal and in May too is usually above normal. In addition, a positive Indian Ocean Dipole event took place – what this means is that the Arabian sea is warmer than normal in relation to the Bay of Bengal seas surfaces near Sumatra. In positive dipole events, usually there is a weak drop in rainfall from June to August and a significant rise from September to November.  So this years, rainfall is following close to the historical averages for a combined El Nino and positive Indian Ocean Dipole event. In addition to this the amplitude of the Madden Julian Oscillation (MJO) in 2015 has been a mixture of very high amplitude events and weak events. When the amplitude is higher than 1 the rainfall is enhanced or suppressed based on the location of the MJO wave. When it is less than 1 MJO is considered to be weak and there shall not be an impact on rainfall. During March- April and June- July the MJO was strong. During February, May, August- September the MJO was mostly weak. Severe drought conditions were not observed during the early Yala season because most parts of the country observed high rainfall in April and May. Significant below average rainfall was only observed in July 2015.

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Weekly Hydro-meteorological Report, 29 October, 2015

Highlights:


Up to 40 mm rainfall was observed in north eastern, western and southern regions of the country during 21st – 27th October. Kalkudah, Kalmunai and Kattankudy received heavy rainfall up to 220 mm on 24th October and rainfall up to 160 mm was observed in the ocean near Trincomalee while Trincomalee received rainfall up to 140 mm on 27th October. Every prediction model predict an increase of rainfall during the next week.
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Weekly Hydro-meteorological Report, 22 October, 2015

Highlights:


Up to 40 mm rainfall was observed in north western, western and southern regions of the country during the time period 14th – 20th October. Gampaha received heavy rainfall up to 160 mm on 18th October and rainfall up to 140 mm was observed in Hikkaduwa. Udawela received rainfall up to 110 mm on 20th October. Every prediction model predict increase of rainfall during the next week.
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Weekly Hydro-meteorological Report, 15 October, 2015

Highlights:


Up to 40 mm rainfall was observed in northern, north eastern, western and south western regions of the country during the time period 7th – 13th October. Nuwara Eliya received heavy rainfall up to 70 mm on 11th October and rainfall up to 90 mm was observed in Ratnapura and Anuradhapura on 13th October. Very heavy rainfall is expected in the central region of the country in the next week. Every prediction model predict an increase in the rainfall during the next week.
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Weekly Hydro-meteorological Report, 8 October, 2015

Highlights:


Up to 40 mm rainfall was observed in northern, north eastern, western, south western and southern regions of the country during the time period 29th September- 5th October. Southern region of Anuradhapura received heavy rainfall up to 110 mm on 25th September and rainfall up to 70 mm was observed in Badulla on 1st October and in Moneragala on 2nd October. Every prediction model predict increase of rainfall during the next week.
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El Nino persists in Pacific as Indian Ocean stays warm

The current El Niño Pacific Ocean warming event is producing sea surface temperatures not seen since the 1997–98 event while the Indian Ocean remains exceptionaly warm, according to the Australian Bureau of Meteorology (BoM).

Tropical Pacific sea surface temperatures are more than 2 °C above average, exceeding El Niño thresholds by well over 1 °C. Most international climate models surveyed by the BoM indicate El Niño is likely to peak towards the end of 2015 and persist into 2016, a story published by the reportingclimatescience.com yesterday.

The tropical Pacific ocean and atmosphere are reinforcing each other, maintaining a strong El Niño that is likely to persist into early 2016. Tropical Pacific sea surface temperatures are more than 2 °C above average, exceeding El Niño thresholds by well over 1 °C, and at levels not seen since the 1997–98 event. In the atmosphere, tropical cloudiness has shifted east, trade winds have been consistently weaker than normal, and the Southern Oscillation Index (SOI) is strongly negative.

Most international climate models surveyed by the Bureau of Meteorology indicate El Niño is likely to peak towards the end of 2015. Typically, El Niño is strongest during the late austral spring or early summer, and weakens during late summer to autumn.

The Indian Ocean Dipole (IOD) is in a positive phase, having exceeded the +0.4 °C threshold for the past 8 weeks. Recent values of the IOD index have been at levels not seen since the strong 2006 positive IOD event. Conversely, the Indian Ocean remains very warm on the broader scale.

Four out of five international models suggest the 2015 positive IOD event will persist until November, when it typically breaks down due to monsoon development.

El Niño is usually associated with below-average spring rainfall over eastern Australia, and increased spring and summer temperatures for southern and eastern Australia. A positive IOD typically reinforces the drying pattern, particularly in the southeast. However, sea surface temperatures across the whole Indian Ocean basin have been at record warm levels, and appear to be off-setting the influence of these two climate drivers in some areas.

Warm anomalies persist along the equator from the South American coast to the Date Line and across most of the Pacific Ocean east of the Date Line in the northern hemisphere. Compared to two weeks ago, sea surface temperature (SST) anomalies have increased slightly in the eastern equatorial Pacific and remain similar in the central and western equatorial Pacific.

Anomalies for the week ending 27 September 2015 exceed +2 °C across most of the equatorial Pacific east of 170°W. Warm anomalies are also present in areas to Australia’s west, and across the majority of the Indian Ocean.

All five NINO indices remain above +1 °C this week, and both NINO3 and NINO3.4 remain at or above +2 °C. NINO3 and NINO3.4 were last at these levels during the 1997–98 El Niño.

Source: www.island.lk

Weekly Hydro-meteorological Report, 1 October, 2015

Highlights:


Up to 40 mm rainfall was observed in south western, western and north eastern regions of the country during the time period 22nd-28th September. Ocean near Kalutara received heavy rainfall up to 160 mm on 25th September and Galle received heavy rainfall up to 120 mm on 28th September. Every prediction model predict decrease of rainfall during the next week.
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Weekly Hydro-meteorological Report, 23 September, 2015

Highlights:


Up to 30 mm rainfall was observed in southern and western regions of the country during the time period 15th-21st September. Southern region of the country received heavy rainfall on 18th September up to 80 mm. Every prediction model predict high rainfall in eastern and south western regions during the next week.
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