Weekly Hydro-meteorological Report, 11 September, 2014

Highlights

Monitoring and Prediction

Rainfall was observed in the southern half of Sri Lanka as well as Jaffna peninsula during 2nd – 8th September. No rainfall was observed in north-central region of the country during this period. Highest rainfall was observed in the area surrounding Ampara. Rainfall expected in the coming week is predicted to be below than the historical average.
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Summary

Monitoring


Weekly Monitoring:: During 2nd- 8th of September rainfall was mostly observed in the southern half of the country. On the 2nd rainfall was observed (up to 40 mm) in a band from Colombo to Ampara across the central mountain with higher rainfall observed in the eastern side. Similar rainfall pattern was observed on the 3rd and 4th with a decrease in rainfall in the western side and central mountains. On the 5th up to 40 mm rainfall was observed concentrated in areas around Chilaw, Ampara and the Jaffna peninsula. Southern regions received rainfall on the 6th with up to 30 mm rainfall observed in Ratnapura. On the 7th light rainfall was observed in western parts of the country. Rainfall was observed in the same regions on the 8th with increased amounts up to 50 mm.


Monthly Monitoring:An above average rainfall was observed throughout the country with higher precipitation observed in the south-western regions of Sri Lanka during August. Highest rainfall during this month was observed in Ratnapura district.

Predictions

14-day prediction:Up to 75 mm rainfall is expected in South-Western and southern Sri Lanka during the fortnight from 10th – 23rd September.

IMD WRF Model Forecast & IRI forecast: According to the IMD WRF model western and south western regions of the country shall receive up to 35 mm rainfall and eastern side of the country shall receive rainfall up to 7.5 mm on the 12th and 13th. IRI models predict up to 50 mm total rainfall for 6 days from 10th- 15th in south western region and up to 75 mm total rainfall in south-western coastal regions and the adjacent sea. But heavy rainfall events are not expected during these six days.

Seasonal Prediction:As per IRI Multi Model Probability Forecast issued in August for the season September to November 2014, Rainfall shall remain climatological while the temperature shall be above normal with 60- 70% probability.

PACIFIC SEAS STATE September 4, 2014 :During July through August the observed ENSO conditions were neutral. Most of the ENSO prediction models indicate warming to El Niño levels coming around early northern fall, peaking at weak strength during winter 2014-15 and lasting into the first few months of 2015.
INDIAN OCEAN STATE :Around 1 degree Celcius above average sea surface temperature was observed around Sri Lanka.
MJO STATE :MJO is weak and therefore shall not influence the rainfall in Sri Lanka.