Weekly Hydro-meteorological Report, 20 December 2012

Highlights

Monitoring and Prediction
Rainfall accumulation of more than 135 mm is expected for the 19th-25thDecember in the eastern half of the island. The monthly predictions point to high rainfall for the period of 20th- 21st of December in the Western slopes and thereafter rainfall shall decrease with time in the Island but considerable amount of rainfall shall persists till 15th of January.

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Summary

Monitoring


Weekly Monitoring: During 12th-17th December, rainfall ranged between 5-210 mm with highest amount of precipitation observed in Nuwara Eliya district on the 16th December. During 15th-17th entire country received heavy rainfall compared to the rest of the days in the week.

Monthly Monitoring: In October, entire Sri Lanka received above average rainfall. Entire country received more than 100 mm of above average rainfall per month and except for South-eastern regions of the island; received 5-80 mm of above average rainfall per month.


Predictions

7-day prediction: During this week, eastern half of Sri Lanka shall receive more than 135 mm rainfall and rainfall shall spreads westward in a reducing pattern. However, entire Island shall receive rainfall of more than 95 mm.

IMD WRF Model Forecast & IRI forecast: For the 21st December, IMD WRF model predicts 36 mm-65 mm of rainfall for the coastal districts starts from Trincomalee to Ampara. For the same day rainfall shall spreads in a reducing pattern towards South-western, North and North-western regions of Sri Lanka. For the same day less than 1 mm of rainfall is predicted for the Central, South, South-western and Western regions of Sri Lanka. On 22nd, IMD WRF model predicts 65 mm-125 mm for coastal regions starts from Batticaloa and Ampara and, spreads as 21st and remaining regions shall receive less than 1 mm of rainfall. NOAA models forecast heavy rainfall for the entire country except for Jaffna Peninsula (mild rainfall) and few patch in Ampara (very heavy rainfall).

1 Month Prediction: Overall- Rainfall shall decrease during 20th-30th with an insignificant fluctuation during 23rd-24th. Thereafter rainfall shall increase gradually till 4th January 2013 and remain constant thereafter till 11th January. Western Slopes- Rainfall shall decrease drastically during 21st-23rd. There onwards rainfall shall increase gradually till 25th and remain constant during 25th-28th. Rainfall shall decrease drastically during 28th-31st. Rainfall shall increase drastically during 1st-4th and thereafter it shall reduce gradually. Eastern slopes- Rainfall shall decrease gradually during 22nd December-1st January. Rainfall is not predicted for 1st-3rd and 8th-13th. During 3rd-5th rainfall shall gradually increase and shall decrease gradually during 5th-8th. Northern- Rainfall shall decrease drastically during 20th-22nd. Rainfall shall increase drastically during 22nd-24th. Thereafter rainfall shall decrease drastically during 24th-27th. Rainfall is not predicted for 27th December 2012-6th January 2013.

Seasonal Prediction: As per IRI Multi Model Probability Forecast for November 2012 to January 2013, issued in November 2012, there is a 50%-60% probability for temperature to be above normal in the country while the rainfall is to be climatological.