Weekly Hydro-meteorological Report, 20 September 2012

Summary

Monitoring

Weekly Monitoring: During the last week (12^th- 17^th September) rainfall ranged between 0 mm- 30 mm. Maximum rainfall of 30 mm observed on 14^th & 15^th for sactterd places of Southern, Western & Southwestern regions of Sri Lanka. Southern half of the island received heavy rainfall on 15^th & 16^th. Scattered rainfall observed during 15^th- 17^th for Jaffna peninsula & North-Eastern regions of the country.

Monthly Monitoring: During August South Western, Western and Some regions of Badulla and Ampara districts experienced an above average rainfall with quite high positive anomaly in the South Western region. The rest of the country experienced below average rainfall during this period.

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Predictions

7-day prediction: During this week, an accumulated rainfall of 25 mm – 95 mm is predicted for the South, Western and Southwestern regions of the island.

IMD WRF Model Forecast & IRI forecast: On the 20^th IMD WRF model predicts less than 65 mm rainfall for Colombo, 2.5-36 mm rainfall for South-Western regions, 2.5- 8 mm rainfall for the South coast and 2.5- 36 mm rainfall for the West. Rainfall shall have the same pattern on the following day (21^st) with increased (35- 65 mm) rainfall for South-Western regions of the country. NOAA models forecast Predicts 20- 50 mm rainfall for Northern, North-Central and North Eastern parts of the country. Rst of the parts shall receive less than 20 mm of rainfall.

1 Month Prediction:  Overall- During 22^nd-24^th rainfall shall show slight increase & shall decrease with same rate. For 24^th-26^th rainfall is not predicted. Thereon it shall increase gradually but it shall show falls during 28^th-29^th September, 5^th-7^th & 13^th-18^th October. Western Slopes- Rainfall shall increase with different rates during 22^nd-28^th. Until 13^th of October, rainfall shall remain around 5 mm with some fluctuations. Rainfall shall further decrease till 15^th & shall increase thereafter. Eastern slopes- Until 1^st of October, rainfall is only expected on 22^nd- 25^th. Rainfall shall increase during 30^th September-3^rd October & it shall decrease till 7^th October with same rate. Thereafter it shall increase till 13^th & shall gradually decrease thereon. Northern- During 22^nd-24^th rainfall shall show slight increase & shall decrease with same rate. Rainfall is not predicted for the period of 29^th September-1^st October. Thereon it shall increase with minor fluctuations till 13^th October. Thereafter rainfall shall decrease gradually.

Seasonal Prediction: As per IRI Multi Model Probability Forecast for September 2012 to November 2012, issued in August 2012, there is a 50%-60% probability for temperature to be above normal in the country while the rainfall is to be climatological.