Weekly Hydro-meteorological Report, 17 December, 2015

Highlights:


High rainfall continued in the entire country during 8th- 14th December week as well but there was a slight decrease in rainfall compared to previous weeks. Heaviest rainfall was recorded on the 14th this week where Gampaha and Badulla districts received very heavy rainfall. NOAA and IRI CFS models predict a significant decrease in the rainfall in the fortnight starting from the 16th. However the MJO is in phase 4 which shall slightly enhance rainfall conditions. IRI further predicts that there shall be below average rainfall during the first quarter of 2016 with 50% probability.
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Summary

Monitoring


Weekly Monitoring:During 8th – 14th December the entire country received rainfall. On 8th December, rainfall up to 90 mm was observed in ocean west of Colombo while Kurunegala district and ocean east of Kalkudah received rainfall up to 80 mm. Western, Central and Sabaragamuwa provinces received up to 40 mm rainfall on the same day. On 9thonly light rainfall was observed in the country. Rainfall up to 130 mm was observed around ocean near Pottuvil on 10th December while Vavuniya and Trincomalee districts received rainfall up to 60 mm. On 11th December, the north-eastern sea received heavy rainfall up to 160 mm. Ocean near Pottuvil received rainfall up to 70 mm on 12th December while Kalutara district received rainfall up to 50 mm. On 13th December Pothuhera received rainfall up to 80 mm and the surrounding area received rainfall up to 50 mm. On 14th December, Bibile region received heavy rainfall up to 200 mm while Gampaha and Kurunegala districts received rainfall up to 140 mm.


Monthly Monitoring::In November 2015, almost entire country received above average rainfall while the ocean near eastern and southern provinces, southern region of Galle and Matara received below average rainfall. Higher above average rainfall was observed in northern region compared to southern region of the country.

Predictions

14-day prediction: NOAA NCEP models predict decrease of the rainfall during 16th – 22nd December compared to past weeks where heavy rainfall was observed. Total rainfall up to 55 mm is expected during the week in eastern and south western regions and total rainfall up to 45 mm is expected in rest of the country. These models predict the rainfall to decrease furthermore during 23rd – 29th December and total rainfall up to 65 mm is expected in northern and eastern regions and total rainfall up to 35 mm is expected in rest of the country.

IMD WRF Model Forecast & IRI forecast: According to the IMD WRF model rainfall up to 125 mm is expected in the coastal region from Trincomalee to Pottuvil on 18th December while the rest of eastern regions shall receive up to 35 mm rain. On 19th December, ocean near Hambantota shall receive rainfall up to 125 mm while south-eastern region of the country shall receive up to 35 mm rain. IRI CFS models predict total rainfall up to 50 mm in central and southern regions of the country during 16th - 21st December. Heavy rainfall is expected in the south-eastern sea during this period.

Seasonal Prediction:As per IRI Multi Model Probability Forecast for January to March, the total 3 month precipitation has 50% likelihood of being below average. The 3 month temperature has more than 70-80% likelihood in the entire country of being in the above-normal tercile during this period.

PACIFIC SEAS STATE December 10, 2015 :During early December 2015 the tropical Pacific SST was at a strong El Niño level. All atmospheric variables strongly support the El Niño pattern, including weakened trade winds and excess rainfall in the east central tropical Pacific. The consensus of ENSO prediction models indicate continuation of strong El Niño conditions during the December-February 2015-16 season in progress. Further strengthening is possible, but not likely, into mid-winter 2015-16, with the event slowly weakening during spring 2016.
INDIAN OCEAN STATE : Neutral sea surface temperature was observed around Sri Lanka.
MJO STATE :MJO phase is in 4 therefore shall slightly enhance rainfall in Sri Lanka.