Weekly Hydro-meteorological Report, 11 July, 2013

Highlights

Monitoring and Prediction
Rainfall was quite heavy in June in the Southern half of Sri Lanka, and July is predicted to be lower although with wetter Southwestern regions in the next week. Compared to the rest of the island, the coastal belts of Puttalam to Galle is likely to receive heavier rainfall on coming two days (12th and 13th of July). Ongoing rainfall shall increase gradually till 14th July & decrease drastically thereafter till 17th. However, significant rainfall events around 14th (peak) & 17th (trough) shall be expected for many regions.

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Summary

Monitoring


Weekly Monitoring:Rainfall ranged between 5-145 mm during 3rd- 9th July 2013. Maximum rainfall observed for Ampara district on 6th July. Entire country experienced rainfall throughout the week and on 6th July North-eastern regions experienced heavy rainfall compared to other regions of Sri Lanka.


Monthly Monitoring:Southern half of the Sri Lanka received an above average rainfall during the month of June. The entire country received less than 15 mm of daily rainfall,with Ratnapura district receiving the highest rainfall during the month(14mm/day).

Predictions

7-day prediction:Southwestern and central hill regions shall receive 5-55 mm of rainfalland during 10th-16th July 2013.

IMD WRF Model Forecast & IRI forecast:For 12thof July, IMD WRF model predicts less than 35 mm of rainfall for coastal regions of Puttalam to Kalutara and it shall spread towards central hills. For the 13th of July, coastal Colombo to Galle districts shall receive 35-65 mm of rainfall and it shall spread as previous day in a reducing manner. NOAA model predicts more rainfall for the Southwestern regions during 9th-14th July compared to rest of the regions of Sri Lanka.

1 Month Prediction:Overall-Ongoing rainfall shall increase gradually till 14th July & decrease drastically thereafter till 17th. However, significant rainfall events around 14th (peak) & 17th (trough) shall be expected. Western Slopes – The rainfall pattern persisting in the entire country shall be observed in this regionwith higher amounts of rainfall. The extreme significant events expected around 14th & 17th July. Western Coast – The rainfall pattern persisting in the entire country shall be observed in this regionwith higher amounts of rainfall. Eastern Slopes– The rainfall pattern persisting in the entire country shall be observed in this regionwith higher amounts of rainfall. Eastern Coast –Ongoing rainfall shall decrease gradually till 17th and shall gradually increase till 20th. However, significant rainfall events are not expected. Northern region- The rainfall pattern persisting in the entire country shall be observed in this regionwith higher amounts of rainfall. But significant events are not expected. Southern Region- The rainfall pattern persisting in the entire country shall be observed in this regionwith higher amounts of rainfall. But amount of rainfall shall be low.

Seasonal Prediction:As per IRI Multi Model Probability Forecast issued on June 2013; for July 2013 to September 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 July 5, 2013 :During Maythrough June observed ENSO conditions remained neutral. Most of the ENSO prediction models indicate a continuation of neutral ENSO into northern autumn. However few models, mainly but not exclusively statistical models, call for cooling towards borderline or weak La-Nina conditions during the coming northern summer season into the latter part of the 2013.

INDIAN OCEAN STATE :The sea surface temperature North-West of Sri Lanka is anomalously cold during 30th June-6thJuly 2013. There is a weak negative Indian Ocean Dipole state with warmer Arabian sea and cold regions around Sumatra.
MJO STATE :MJO is entering phase 2 and is likely to enter phase 3 both of which influences Sri Lanka rainfall. However, the signal is modest at present but bears watching.