Weekly Hydro-meteorological Report, 20 November 2012

Highlights

Monitoring and Prediction
Monitoring: Heavy rains have persisted in Sri Lanka since the start of October – this as expected during an El Nino phase and a positive Indian Ocean Dipole mode phase (with warmer sea surfaces in the Arabian seas). Prediction: Rainfall shall be higher than normal for the rest of November. During December, since the El Nino state tends toward neutral and the IOD influence is minimal, the rainfall is likely to be near normal. Warmer than normal temperatures persist due to the warm Arabian sea surface anomalies.

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Summary

Monitoring


Weekly Monitoring: During 13th- 16th of November rainfall was observed on the entire island, with maximum rainfall within this period observed on the 15th. On the 17th, no rainfall was observed on the Northern half of Sri Lanka while heavy rains continued on the Southern half of the country. By the 18th rainfall desisted completely with the exception of some areas in the south which received light rainfall. Maximum rainfall (around 90 mm) for the week was observed on the 17th in Uda-Walawe region.

Monthly Monitoring: In October, a high positive rainfall anomaly was observed on the entire country. Surplus rainfall upto 150 mm was observed in all parts of the country with the exception of Uva region which received less rainfall than the rest of the country.


Predictions

7-day prediction: During this week, an accumulated rainfall over 65 mm is predicted on the South western region of the island. The rest of the country shall receive rainfall upto 65 mm.

IMD WRF Model Forecast & IRI forecast: No updates available for WRF model forecasts. NOAA models forecast 20 mm rainfall for the entire country.

1 Month Prediction: Overall- Rainfall shall increase until the 3rd of December and then shall decrease thereafter. Western Slopes- Rainfall shall increase until 24th November and then shall decrease during the next 3 days. Then once again an increase of rainfall is expected until the 10th of December. Thereafter rainfall shall decrease. Eastern slopes &Northern- Rainfall shall follow a similar pattern to the overall rainfall on the island. In these regions peak amounts of rainfall are observed on the 15th and 2nd December respectively.

Seasonal Prediction: As per IRI Multi Model Probability Forecast for December 2012 to February 2013, issued in November 2012, there is a 60%-70% probability for temperature to be above normal in the country while the rainfall is to be climatological.