Weekly Hydro-meteorological Report, 09, June 2016

Highlights: Previous week was dry except rainfall on the 3rd and 7th of June. The highest rainfall up to 70 mm was seen around Balangoda on the 3rd. The Temperature was highest (35- 40 0C) in the eastern coastal area and was lowest in the hill country (15- 20 0C) in the previous week. NOAA NCEP models predict up to 125mm total rainfall in south western region in the next week while other regions shall have up to 85mm rainfall. NOAA CPC GFS model predicts 35- 40 0C maximum temperature near Ampara town and surrounding regions during next week. The wind shall be easterly with speed around 15 m/s. MJO is expected to remain weak in the next two weeks but shall be in the Indian Ocean. Therefore, a slight enhancement is expected in rainfall due to this factor.

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Monitoring
Rainfall
Weekly Monitoring:1^st- 7^th June was a dry week except slight rain on the 3^rd and 7^th. No rainfall was seen during 1^st-2^nd and 4^th-6^th June, while on the 3^rd, up to 70 mm rainfall was seen near Balangoda. Nittambuwa and surrounding cities. The western sea region received up to 60 mm rainfall while Western region of Colombo, northern region of Ratnapura and eastern region of Kalutara experienced up to 30 mm rainfall on the 7^th. Based on the CPC Unified Precipitation Analysis, up to 75 mm total rainfall was seen around Puttalam and surrounding regions. According to the RFE 2.0 model, up to 100 mm total rainfall was received in Kegalle and up to 75 mm total rainfall was seen in surrounding regions in the same week. It recorded up to 100 mm of total rainfall anomaly in central Kegalle and 100 mm in nearby cities.

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 ~600mm monthly excess rainfall than the historical average. CPC Unified Precipitation Analysis also recorded up to 750 mm total rainfall in the same regions. According to RFE2, up to 750 mm of total monthly rainfall was received in Kegalle and Gampaha while the surrounding regions experienced up to 500 mm total rainfall during the month. Northern region of the country received 6 times more rainfall than the historical average and north western province and Matale received 4 times more rainfall. Nearly 400mm of accumulated average monthly precipitation was recorded as above normal historical average in May. During 1^st -19^th May, above average rainfall was received while the highest daily average precipitation in the entire country was recorded as 120 mm on the 15^th. 

Temperature
The highest maximum temperature was seen along northern and eastern sea as 35- 40 ⁰C during 29^th May- 4^th June.  Kandy and Nuwara Eliya region experienced low maximum temperature as 20 ⁰C while the maximum temperature in the rest of the country was between 30- 35 ⁰C. Entire country has experienced 25- 30 ⁰C of minimum temperature except Kandy, Nuwara Eliya, Ratnapura and surrounding districts. The mean temperature in South western, northern and central regions of the country was between 1⁰C- 3 ⁰C during this week

Wind

During the week, southern most region of the country experienced 15 m/s total Easterly wind while northern region received up to 10 m/s wind with the same direction in 850 mb level. At to the 700mb level, bottom part of the country received 10 m/s wind while northern most region received up to 5 m/s wind.  

Ocean State

Pacific seas state: May 19, 2016

During mid-May 2016 the positive tropical Pacific SST anomaly was quickly weakening, now indicating only a weak El Niño. The atmospheric variables continue to support the El Niño pattern, but at much reduced strength. This includes only a mildly weakened Walker circulation and excess rainfall in the central tropical Pacific, failing to extend eastward as it did in previous months. Most ENSO prediction models indicate a return to neutral by the end of May, with likely development of La Niña (of unknown strength) by fall. (Text Courtesy IRI)

Indian Ocean State

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

Predictions

14-day prediction:NOAA NCEP models predict up to 125mm total rainfall in south western region while up to 55 mm total rainfall is expected in northern, southern and eastern regions of the country during 8^th– 14^th June. Again rainfall shall increase during 15^th – 21^st June. More than 135 mm total rainfall is expected in Colombo, Gampaha, Kegalle and nearby regions during this week while the other regions shall receive up to 85 mm rainfall.

Numerical weather prediction: NWP model predicts up to 80mm rainfall around Ratnapura on the 10^th while surrounding regions shall have up to 40 mm of rainfall. Up to 40m rainfall is expected around Ratnapura, Gampaha, Colombo and Kalutara during 11^th- 12^th June. On the 13^th, up to 40 mm of rainfall is expected in Western province districts and around Ratnapura. 

 

IMD WRF Model Forecast & IRI forecast:According to the IMD WRF model, there shall be up to 35mm total rainfall along the coastal stretch between Puttalam and Galle during 10^th – 11^th. The IRI CFS model predicts up to 75 mm total rainfall in the sea near Galle while the nearby regions shall have up to 50 mm total rainfall for 8^th- 13^th June.
 Seasonal Prediction:As per IRI Multi Model Probability Forecast for June to August, 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 near Ampara town and surrounding regions during 10th- 16th June and 30- 35 ⁰C maximum temperature along north, east and south of the country. Maximum temperature in the hill country shall be bet ween 20- 25 ⁰C. During the same week, minimum temperature is expected around Nuwara Eliya and Ratnapura to be 15- 20 ⁰C while in Uva, Central, Sabaragamuwa and Western provinces it shall be 20- 25 ⁰C.

Wind

There shall not be a big change in the wind pattern in the next week compared to this week. NOAA CPC GFS models at 850 mb and 700 mb levels forecast 15 m/s of wind during 10th – 16th June which is easterly.   

MJO based OLR predictions

On the 7^th, MJO is in phase 8, therefore it shall suppress rainfall in Sri Lanka. MJO prediction models predict that the MJO shall be in the Indian Ocean in next 15 days. The MJO is expected to remain weak in the next two weeks. Therefore, the impact of MJO on the rainfall in Sri Lanka shall be minimal. During first 5 next days, MJO shall suppress rainfall in the country. During 13^th-17^th June, it shall not have a significant impact on the rainfall while it shall slightly enhance rainfall in Sri Lanka during 18^th-22^nd June.