Weekly Hydro-meteorological Report, 03 September, 2015

Highlights:


Up to 40 m rainfall was observed in various parts of the country during the previous week. Rainfall was mostly observed in the south western region of the country and also in the northern region. Every prediction model predict an increase in rainfall during the next week. Heavy rainfall events are also predicted in Polonnaruwa district during the next week.
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Summary

Monitoring


Weekly Monitoring:During 26th- 28th of August rainfall was observed in south western region of Sri Lanka. On the 26th up to 20 mm rainfall was observed in the southern province and up to 30 mm rainfall was observed in Gampaha and Kegalle districts. Then on the 27th rainfall decreased in these areas and only up to 10 mm rainfall was observed. Rainfall continued on the 28th as well. Ratnapura and Kandy districts received up to 40 mm rainfall on this day while the rest of south western region received up to 10 mm rainfall. Only light rainfall was observed on 29th and 30th. On 31st August and 1st September up to 40 mm rainfall was observed in Vavuniya and Mullaitivu districts while the rest of the country only received light rainfall.


Monthly Monitoring::In August 2015 most of south western and north western as well as north central regions received above average rainfall. Colombo district as well as central and eastern provinces received below average rainfall. Highest rainfall was observed in Ratnapura district. Southern sea of the country also received above average rainfall during this month.

Predictions

14-day prediction: NOAA NCEP models predict relatively high rainfall in the south western region of the country compared to the rest of the country during 3rd- 9th September. There shall be about 45 mm total rainfall during this week. These models predict a further increment in rainfall during the following week (10th- 16th) where up to 55 mm total rainfall is expected in the entire country.

IMD WRF Model Forecast & IRI forecast: According to the IMD WRF model high rainfall (up to 65 mm) is expected in Mullaitivu and Trincomalee districts on 5th of September. Surrounding regions as well as the south western region shall receive up to 35 mm rainfall on the same day. Light rainfall is expected in other regions. Rainfall shall decrease on the 6th but still Mullaitivu district shall receive up to 35 mm rainfall. No rainfall is expected in other regions of the country except in surrounding areas of Mullaitivu where light rainfall is possible. IRI CFS models predict rainfall up to 150 mm in Badulla region and up to 100 mm in Polonnaruwa, Ampara, Batticaloa and Trincomalee districts during 1st- 6th September. These amounts are totals for given 6 days. Furthermore heavy rainfall events are predicted in Polonnaruwa district during this period.

Seasonal Prediction:As per IRI Multi Model Probability Forecast for September to November, the total 3 month precipitation shall be climatological. 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 August 20, 2015 :During late July through early-August 2015 the SST was at a strong El Niño level. All atmospheric variables 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 August-October 2015 season in progress. Some further strengthening into fall is likely, with the event lasting into spring 2016.
INDIAN OCEAN STATE : 1 0C above average temperature was observed around Sri Lanka.Indian Ocean Dipole is also active.
MJO STATE :MJO is weak and therefore shall not influence the rainfall in Sri Lanka.