Weekly Hydro-meteorological Report, 5 September, 2013

Highlights

Monitoring and Prediction
Puttalam to Kalutara districts are likely to receive heavy rainfall on coming two days (6th & 7th September). However, Jaffna, Batticaloa, Northern Ampara and Badulla districts shall receive high amount of predicted rainfall during 2nd-7th. Ongoing rainfall is likely to increase gradually during 29th August-1st September. Thereafter rainfall shall decrease till 7th. For the entire country, ongoing rainfall is likely to increase gradually till 10th September and shall remain more or less constant (4-6 mm/day) during 10th-13th. No significant rainfall events are predicted for the entire country, except for the western coasts and eastern slopes during 12th-14th and 9th-11th September, respectively.

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Summary

Monitoring


Weekly Monitoring:Weekly monitoring of rainfall for previous week (28th August-5th September) was not available. However, during 21st-27th August 2013, rainfall ranged between 5-80 mm. Entire country received rainfall during 27th August, except for coastal districts of Northern, Northeastern, Eastern, Southeastern and South of the island, which was dry.


Monthly Monitoring:Southwestern regions of Sri Lanka received an above average rainfall during the month of July. The entire country received less than 15 mm of daily rainfall, with Colombo and Gampaha districts receiving the highest rainfall during the month (14 mm/day).

Predictions

7-day prediction:Southern 2/3rd of the island shall receive 5-55 mm of rainfall and remaining parts of the island shall receive 55-85 mm of rainfall during 4th-10th September 2013.

IMD WRF Model Forecast & IRI forecast:For 6th of September, IMD WRF model predicts less than 36 mm of rainfall for the coastal regions of Puttalam-Kalutara districts and shall spread to nearby regions (including Jaffna peninsula) in a reducing manner. For 7th of September, same model predicts less than 65 mm of rainfall for the coastal regions of Puttalam-Colombo districts and shall spread to nearby regions in a reducing manner. NOAA model predicts high rainfall (25-50 mm/week) for Jaffna, Batticaloa, Northern Ampara and Badulla districts during 2nd-7th September.

1 Month Prediction:Overall- Ongoing rainfall is likely to increase gradually till 10th September and shall remain more or less constant (4-6 mm/day) during 10th-13th September. No significant rainfall events are expected. Western Slopes –Rainfall is likely to increase gradually till 13th September and no significant rainfall events are expected. Western Coast – The rainfall pattern persisting in western slopes shall be observed in this region and significant event is likely to observe during 12th-14th September. Eastern Slopes– Rainfall shall increase drastically till 10th September and shall decrease in same rate thereafter. However, significant rainfall event is likely to experience during 9th-11th September. Eastern Coast – The rainfall pattern persisting in western slopes shall be observed in this region, with low amount of rainfall. Northern region- The rainfall pattern persisting in western slopes shall be observed in this region, with low amount of rainfall. Southern Region- Rainfall is likely to increase after 8th and shall persist till 13th. Comparatively low amount of rainfall shall observe in this region.

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

PACIFIC SEAS STATE August 15, 2013 :During July through early August the observed ENSO conditions remained neutral. Most of the ENSO prediction models indicate a continuation of neutral ENSO through the remainder of 2013 & into early 2014. However, a few (mainly statistical) models call for cooling towards borderline or weak La-Nina conditions for northern autumn into winter. While a few others (mainly dynamical) forecast some warming towards borderline or weak El-Nino conditions for this same time frame.

INDIAN OCEAN STATE :The sea surface temperature around Sri Lanka was neutral during 25th-31st August 2013.
MJO STATE :MJO is at phase 1 and it is likely to enter phase 2 in next few days which influences Sri Lanka rainfall.