Weekly Hydro-meteorological Report, 29 November 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: On the 21st of November, rainfall was observed in south western region in Sri Lanka. Then on the 22nd rainfall in this region increased upto 40 mm. Light rainfall was observed in Jaffna peninsula and north central regions while heavy rainfall was observed in western regions on the same day. On the 23rd and 24th, the entire country received rainfall with the exception of south eastern region. On the 25th heavy rainfall was observed throughout the country with upto 120 mm rainfall observed in Batticaloa and Moneragala regions. Heavy rainfall continued on the 26th of November with maximum rainfall observed in the northern Sri Lanka.

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 85 mm is predicted for south western regions and upto 55 mm for the rest of the country.

IMD WRF Model Forecast & IRI forecast: On the 30th of November Southern regions of Sri Lanka shall receive rainfall upto 35 mm while on the 1st of October rainfall (upto 7.5 mm) is only predicted in South Eastern regions of the country.

1 Month Prediction: Overall- Rainfall shall increase until the 1st of December and then shall fluctuate with a decreasing trend afterwards. Western Slopes- Rainfall shall increase until 1st December and shall remain almost constant until 18th Dec. with minor fluctuations. Thereafter shall decrease until the 25th. Eastern slopes & Northern- Rainfall shall follow a similar pattern to the overall rainfall for the island.

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.