Weekly Hydro-meteorological Report, 5, May 2016

Highlights:


Up to 40 mm high rainfall was received by Colombo, Gampaha, Kegalle, Kurunrgala and Anuradhapura districts during the previous week. Galle and Matara districts also received up to 30 mm rainfall and apart from that more than 10 mm rainfall was not seen in the country. In April 2016 the entire country received below average rainfall except for Colombo, Gampaha and Ratnapura districts. The rainfall is expected to increase in the next two weeks. The high temperature shall continue in the country as the probability of having above average temperature remains high.
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Summary

Monitoring


Weekly Monitoring:On 27th of April 2016 only up to 10 mm light rainfall was seen in various parts of the country. On the 28th eastern regions of Gampaha and the Kandy/ Kurunegala/Matale districts border received up to 30 mm rainfall while the surrounding regions received up to 15 mm rainfall. Once again slight rainfall was seen on the 29th. Kegalle, Colombo, Gampaha and Kurunegala districts received heavy rainfall up to 40 mm on the 30th while Kalutara, Ratnapura, Kandy and Puttalam districts received up to 30 mm rain along with the sea close to Colombo/ Gampaha. Galle and Matara districts received up to 20 mm rainfall on the 1st of May. Anuradhapura district received up to 40 mm rainfall on the 2nd. Eastern region of Matara district and Kuruwita region received up to 30 mm rain on the same day. Gampaha and Colombo districts received up to 30 mm rainfall on the 3rd.


Monthly Monitoring:During April 2016 the entire country received below average rainfall except Ratnapura, Colombo and Gampaha districts. These districts received up to ~120 mm excess rainfall than the historical average.

Predictions

14-day prediction:NOAA NCEP models predict up to 45 mm total rainfall during 4th – 10th May in the south western region of the country while the rest of the country may not receive significant rainfall during this period. Rainfall shall increase during the following week (11th- 17th May) and during this period up to 85 mm total rainfall is expected in the same region.

IMD WRF Model Forecast & IRI forecast:According to the IMD WRF model, up to 125 mm rainfall is expected in Ginigathhena area while Kegalle and Ratnapura areas shall have up to 65 mm rain on the 7th. The south western, central and north western region shall receive up to 35 mm rain on this day. Rainfall shall reduce on the 8th. There shall be up to 65 mm rainfall Ginigathhena, Ratnapura and Kegalle areas, but the rainfall shall be more localized. Surrounding region shall receive up to 35 mm rain. The IRI CFS model predict up to 100 mm total rainfall in the central to south eastern region of the country.

Seasonal Prediction:As per IRI Multi Model Probability Forecast for May to July, 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 April 21, 2016 :During mid-April 2016 the positive tropical Pacific SST anomaly was weakening, now indicating only a moderate strength El Niño. All atmospheric variables continue to support the El Niño pattern, but at reduced strength. This includes weakened trade winds and excess rainfall in the east-central tropical Pacific, extending eastward to a lesser extent than last month. Most ENSO prediction models indicate continued weakening El Niño conditions during the rest of the northern spring season, returning to neutral by late spring or early summer 2016, with La Niña development likely by fall.
INDIAN OCEAN STATE :1 degrees C above average sea surface temperature was observed around Sri Lanka.
MJO STATE :MJO is weak and therefore it shall not affect the rainfall.