Weekly Hydro-meteorological Report, 29 August, 2013

Highlights

Monitoring and Prediction
During past week (20th-26th August) rainfall was quite low compared to the month of July. Ratnapura and Nuwara Eliya districts are likely to receive heavy rainfall on today (29th August) compared to rest of the regions of Sri Lanka. However, Matara-Batticaloa and Puttalam-Jaffna districts shall receive lowest amount of predicted rainfall during 29th-30th August. Ongoing rainfall is likely to increase gradually during 29th August-1st September. Thereafter rainfall shall decrease till 7th September. No significant rainfall events are predicted for the entire country, except for the Eastern slopes and coasts during 1st August-3rd September.

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Summary

Monitoring


Weekly Monitoring:Rainfall ranged between 5-10 mm during 20th-26th August 2013. Maximum rainfall observed in Northern half of the island on 26th August. However, entire Sri Lanka showed dry condition during this period compared to month July.


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:Southwestern regions of Sri Lanka shall receive 5-45 mm of rainfall and shall spread northeastward in a reducing manner during 27thAugust-2nd September 2013.

IMD WRF Model Forecast & IRI forecast:For 29th of August, IMD WRF model predicts less than 65 mm of rainfall for the border between Ratnapura and Nuwara Eliya districts and it shall spread island wide in a reducing manner, except for Matara, Puttalam, Kurunegala, Mannar, Kilinochchi, Jaffna (less than 1mm/day). For 30th of August, same model predicts less than 36 mm of rainfall for the entire country, except for Matara-Batticaloa and Puttalam-Jaffna districts (less than 1 mm/day). NOAA model predicts high rainfall (75-100 mm/week) for Kandy, Badulla and Nuwara Eliya districts and shall spread in a reducing manner towards Trincomalee district during 27th August-1st September.

1 Month Prediction:Overall- Ongoing rainfall is likely to increase gradually during 29th August-1st September. Thereafter rainfall shall decrease till 7th September. No significant rainfall events are expected. Western Slopes – The rainfall pattern persisting in entire country shall be observed in this region. Western Coast – Ongoing rainfall is likely to increase gradually during 29th August-5st September with a dropdown during 1st-3rd September. Eastern Slopes– Rainfall shall increase drastically during 29th August-1st September and significant rainfall event is likely to experience during 31st August-2nd September. Thereafter rainfall shall reduce till 4th and remain constant. Eastern Coast – The rainfall pattern persisting in entire country shall be observed in this region. However, significant rainfall event is likely to experience during 1st-3rd September. Northern region- The rainfall shall increase drastically during 29th August-2nd September and thereafter shall decrease in a same rate. Southern Region- The rainfall shall increase gradually till 5th September and thereafter shall decrease till 7th September.

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 18th-24th August 2013.
MJO STATE :MJO is at phase 1 and 8 and shall not influence the rainfall of Sri Lanka.