Weekly Hydro-meteorological Report, 24 December, 2014

Highlights

Monitoring and Prediction

A significant increase in rainfall was observed during the previous week with Anuradhapura, Polonnaruwa, Batticaloa and Wilpattu areas receiving rainfall around 200 mm. High rainfall is expected to persist in the eastern regions of Sri Lanka until around 29th of December, and thereafter a significant decrease in rainfall is expected throughout the country. Extremely heavy rainfall is expected on the 27th in the sea about 300 km east of Sri Lanka.
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Summary

Monitoring


Weekly Monitoring::On the 15th of December significant rainfall was only observed in Ratnapura & Kaluthara districts. Thereafter rainfall increased significantly throughout the country. Extremely heavy rainfall was observed during 16th-21st December in eastern and north central regions. Anuradhapura, Polonnaruwa and Batticaloa regions received highest rainfall during this week with amounts received exceeding 200 mm on the 19th. Rainfall decreased slightly on the 20th but still coastal areas of Batticaloa received rainfall up to 140 mm. Again on the 21st rainfall increased with highest rainfall of about 180 mm observed in Wilpattu area.


Monthly Monitoring:An average rainfall of 16 mm-18 mm was observed throughout the country with higher precipitation observed in the north-eastern regions of Sri Lanka during November. Highest rainfall during this month was observed in Northern and Eastern provinces. Also the decadal rainfall average was increased from 18 mm to 9 mm within a week.

Predictions

14-day prediction:NOAA NCEP models predict further very heavy rainfall in the eastern regions of Sri Lanka exceeding 135 mm during 23rd- 29th December. The rest of the country shall receive up to 135 mm of rainfall. However during the week 30th December- 5th January, rainfall is expected to decrease significantly with only rainfall up to 55 mm expected throughout the country.

IMD WRF Model Forecast & IRI forecast:According to the IMD WRF model, Region from the east coast to west coast across the central mountains shall receive rainfall up to 125 mm during 26th of December. Ampara area shall receive more than 125 mm rain on the same day and the rest of the country shall receive rainfall up to 35 mm. On the 27th December rainfall is expected to cease throughout the country except in eastern coastal areas where light rainfall is expected. But extremely high rainfall is expected in the sea about 300 km off the eastern coast of Sri Lanka

Seasonal Prediction:As per IRI Multi Model Probability Forecast for December to February, the total 3 month precipitation shall be climatological. The 3 month average temperature has more than 70% likelihood of being in the above-normal tercile during this period.

PACIFIC SEAS STATE December 18, 2014 :During November through early December the SST exceeded thresholds for weak Niño conditions, although only some of the atmospheric variables indicate an El Niño pattern. Most of the ENSO prediction models indicate weak El Niño conditions during the December-February season in progress, continuing through most or all of northern spring 2015.
INDIAN OCEAN STATE :Around 0.5 degrees C above average SST was observed in the south-eastern sea of Sri Lanka.
MJO STATE :MJO is in Phase 3- Indian Ocean and therefore shall enhance the rainfall in Sri Lanka.