Weekly Hydro-meteorological Report, 23, June 2016

Highlights: The entire country received below average rainfall during the previous week except the south-western region of the country. During the previous week maximum temperature of 35-40⁰C was seen along the eastern coastal belt while the minimum temperature of 20⁰ C was recorded in NuwaraEliya.NOAA NCEP models predict up to 55mm total rainfall in the western province in the next week while other regions shall have up to 45mm rainfall. NOAA CPC GFS model predicts 35- 40 ⁰C maximum temperature along the coastal region in the eastern side of the island.Higher wind speed (up to 20 m/s) is expected throughout the country and the surrounding sea. MJO shall enhance rainfall conditions up to 10 days ahead and thereafter shall suppress. ENSO is neutral and therefore the impact on the rainfall is minimal. La Nina conditions are expected to develop by late June which shall slightly enhance rainfall in the country during July and August.

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Monitoring
Rainfall

Weekly Monitoring:No rainfall received on the 15^th and on the 16^thin the country except up to 10 mm rain in Kurunegala District. Up to 30mm of rainfall was received on the 17^thby Matara, Galle and adjacent sea. No rainfall was received by the entire island on the 18^thexcept up to 30 mm of rainfall seen in Ampara district and the north eastern sea. The entire country did not receive any rain on the 19^th.The south-western and central regions of the country received up to 50 mm of rainfall on the 20^th. On the 21^st, no rainfall was received by the entire island. Based on the CPC Unified Precipitation Analysis,a total precipitation of up to 45mm was seen in south western region of the country where as the total precipitation of western and central regions of the country went only up to about 25mm.According to the RFE2.0 model, Galle, Matara and Ratnapura districts receivedup to 75 mm total rain, which was above average, while western, south-eastern and central region received up to 25 mm total rainfall. The models show25 mm of total rainfall anomaly in Matara district and the Southern sea close to it.

Monthly Monitoring:Entire country received more rainfall than the historical average during May 2016. The districts in western, north western and north central provinces received up to ~450mm monthly excess rainfall than the historical average. CPC Unified Precipitation Analysisand RFE2.0 model (during 23^rd May- 21^st June)recorded up to 500 mm total rainfall in Kalutara and Colombo Districts while 150-300 mm total rainfall was recorded in the rest of western region. A total precipitation of 75-100mm was recorded in the central region of the country while the total precipitation adds up to 25mm in the rest of the country. Western and north western provinces received 2 times more rainfall than the normal level. However the northern and the eastern regions received only about 5% of the normal rainfall.During 23^rd May- 21^st June, highest precipitation was received on 27^th of May.

Temperature

During the week from 12^th to 18^th highest maximum temperature was seen as 35-40⁰C along the eastern and north eastern coastal band of the island. NuwaraEliyaregion experienced low maximum temperature as 20 ⁰C while the maximum temperature in the rest of the country was between 30- 35 ⁰C during the week. The minimum temperature of 20 ⁰C was recorded in NuwaraEliya.The mean temperature during this week was 1- 3 ⁰C above average in the entire southern half as well as the north-western region of the country.

Wind

Entire country experienced 15 m/s total westerly windat the 850 mb levelduring the previous week while northernregion received up to 10 m/s wind innorth westerlydirection at the 700mb level and 6-10 m/s in the rest of the country. 

Ocean State

Pacific seas state: May 19, 2016

During mid-June 2016 the tropical Pacific SST anomaly was near zero, indicating ENSO-neutral conditions. The key atmospheric variables also indicate neutral ENSO condition. This includes near-average upper and lower level tropical Pacific winds, as well as near-normal cloudiness and rainfall patterns in the central and eastern equatorial Pacific. Most ENSO prediction models indicate neutral ENSO conditions during June, with likely development of La Niña (of unknown strength, but likely weak) by late July or August, lasting through fall and into winter. (Text Courtesy IRI)

Indian Ocean State

0.5⁰C above average sea surface temperature was observed around Sri Lanka.

Predictions

14-day prediction:NOAA NCEP models predict up to 65mm total rainfall in the western province while the north western and central provinces may experience between 35-45mm total rainfall during 22^nd – 28^thJune. There will be less than 25 mm rainfall in the Jaffna region. The total rainfall shall continue to remain the same over the course of next seven days starting from the 28^thexcept for the Jaffna region.

Weekly prediction: IMD GFS model predicts up to 40mm rainfall in the western region of the country on the24^thand up to 20 mm during 25^th-26^th June.The rest of country would not be experiencing considerable amount of rainfall during that period.On 27^th and 28^thless than 10 mm rain is expected in the south- western region of the country.Up to 40mm rainfall is expected around Kalutara and Colombo districts during 29^th- 30^th June.

IMD WRF Model Forecast & IRI forecast:According to theIMD WRF model, there shall be up to 65mm rainfall near Ratnapura and Kegalle districts while western, north central and central regions shall receive up to 35 mm rainfallon25^th&26^th of June. No extreme rainfall conditions are experienced over the next week. Colombo district will receive a total precipitation of 50mm along with the Jaffna region during the coming week. Up to 200 mm of total rainfall shall experience in the north eastern sea region during 22^nd- 27^th June.

 Seasonal Prediction:As per IRI Multi Model Probability Forecast for July to September, the total 3-month precipitation shall be climatological. The 3-month temperature has more than 70-80% likelihood in the entire country of being in the above-normal tercile during this period.

Temperature

NOAA CPC GFS model predicts 35- 40 ⁰C maximum temperature along the coastal belt in the Eastern side of the country as well as in Ampara and MonaragalaDistricts.The remaining northern part of the country will experience a maximum temperature of between 30- 35 ⁰C. Maximum temperature in the hill country and the Western province shall be between 20- 25 ⁰C. During the same week, minimum temperature is expected around NuwaraEliyaand Badulla to be 15- 20 ⁰C while in Batticaloa and Hambantota it shall be 25-30⁰C. The minimum temperature in the rest of the country shall be 20-25⁰C.

Wind

The wind speed shall increase up 20 m/s in the entire country as well as the surrounding sea during 22^nd – 29thJunein both 850 mb and 700 mb levels.

MJO based OLR predictions

MJO shall be in the Indian ocean in the next 10 days. There shall be a strong enhancement of rainfall conditionsdue to the MJO in the next 5 days and the enhancement shall be less during day 6- 10 in the future. Thereafter the MJO shall move to the Maritime Continent after the 10^th day and therefore there shall be slight suppression in rainfall conditions.