Weekly Hydro-meteorological Report, 28, April 2016

Highlights:


Rainfall was received only in south western and north central regions of the country on 20th and 21st April but there was no rainfall during 22nd -26th. Highest rainfall of 90 mm was seen near Hanwella and surrounding regions on 21st April. NOAA NCEP models predict up to 65 mm rainfall in south western region of the country during 27th– 26th April. MJO is weak so there shall be no effect on rainfall by the MJO.
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Summary

Monitoring


Weekly Monitoring:Rainfall was received in south western region and north central province of the country on 20th and 21st April but no considerable rainfall was seen during 22nd- 26th April. On the 20th, near Ratnapura town, Anuradhapura city and surrounding areas received up to 40 mm rainfall while up to 30 mm rainfall was received in south eastern sea around Kirinda. Up to 90 mm rainfall was seen in Hanwella and surrounding regions while up to 70 m rainfall received in southern region of Colombo, Avissawella, Pannipitiya and surrounding regions on the 21st. Central region of Anuradhapura and the sea west of Colombo district received up to 30 mm rainfall on the same day. No rainfall was seen on the 22nd. Up to 20 mm slight rainfall received only in Kalutara and northern region of Galle on 23rd April. 24th and 25th April were mostly dry and again up to 20 mm rainfall was seen in Maho and western region of Anuradhapura on the 26th.


Monthly Monitoring:During March 2016 most regions of the country received below average rainfall. Rainfall received by Ratnapura, Kalutara, northern regions of Colombo and Galle, western and southern regions of Puttalam was about 10 mm/day less than the historical average for this month. Above average rainfall was only seen in Kegalle, western region of Kandy, southern region of Matale and the south eastern region of Kurunegala district.

Predictions

14-day prediction:NOAA NCEP models predict up to 65 mm rainfall in the south western region of the country during 27th April- 3rd May and 4th-10th May.

IMD WRF Model Forecast & IRI forecast:According to the IMD WRF model, up to 35 mm rainfall is expected near Colombo and Kalutara and the sea west of Puttalam on 29th of April while the rest of the country shall receive a slight rainfall except northern and eastern regions. On 30th April, the models predict no rainfall in the entire country but up to 65 mm rainfall in the sea west to Puttalam. IRI CFS model predicts up to 75 mm total rainfall around Badulla during 27th April – 2nd May while up to 50 mm rainfall is expected around Kandy, Eastern region of Ratnapura and Nuwara Eliya.

Seasonal Prediction:As per IRI Multi Model Probability Forecast for May to July, 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.

PACIFIC SEAS STATE April 21, 2016 :During mid-April 2016 the positive tropical Pacific SST anomaly was weakening, now indicating only a moderate strength El Niño. All atmospheric variables continue to support the El Niño pattern, but at reduced strength. This includes weakened trade winds and excess rainfall in the east-central tropical Pacific, extending eastward to a lesser extent than last month. Most ENSO prediction models indicate continued weakening El Niño conditions during the rest of the northern spring season, returning to neutral by late spring or early summer 2016, with La Niña development likely by fall.
INDIAN OCEAN STATE :1 degrees C above average sea surface temperature was observed around Sri Lanka.
MJO STATE :MJO is weak and therefore it shall not affect the rainfall.