Weekly Hydro-meteorological Report, 06 December 2012

Highlights

Monitoring and Prediction
Monitoring: Heavy rains have persisted in Sri Lanka since the start of October – this as expected during 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 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: 5-165 mm of rainfall was observed during previous week (28th November-3rd December). On 29th of November Southern half of the Sri Lanka received 5-70 mm of rainfall. On 3rd December Northern and North-central regions received higher rainfall compared to rest of the days. However, maximum rainfall of 165 mm was observed for the belt in between Puttalam and Gampaha districts on 3rd December.

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 around 5-95 mm is predicted for entire country except for the North-western regions of Sri Lanka.

IMD WRF Model Forecast & IRI forecast: On the 8th of December South-eastern regions shall experience rainfall of 36 mm of rainfall and rainfall shall decrease towards the center of the island. For the same day 36 mm of rainfall is predicted for the Colombo district. On 9th of December 8 mm and 36 mm of rainfall is predicted for the Eastern and Western, South-western regions, respectively. For this week IRI forecast is not available.

1 Month Prediction: Overall- Rainfall shall decrease gradually during 6th-13th December with minor fluctuation during 8th-9th. Rainfall shall increase during 13th-17th & it shall decrease drastically till 20th. Western Slopes- Rainfall shall decrease gradually during 6th-13th December. Rainfall shall increase during 13th-17th & it shall decrease drastically till 20th. Eastern slopes & Northern- For the eastern slopes rainfall shall decrease drastically during 6-12th and during 12th-15th rainfall shall remain constant. Rainfall shall increase gradually till 18th and shall decrease during 18th-22nd. For the wester slopes rainfall shall increase gradually during 6th-9th and it shall decrease gradually till 13th. Therafter rainfall shall increase till 17th and it shall decrease drastically during 17th-20th December.

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.