Weekly Hydro-meteorological Report, 19, May 2016

Highlights:


Most of the regions received high rainfall during 11th – 17th May while up to 200mm highest rainfall was seen in Colombo, Gampaha, Kalutara northern region of Anuradhapura on 15th May. Extreme rainfall conditions were seen in the entire country during the previous week. The rainfall is expected to decrease in the next week with heavy rainfall in south western region of the country. MJO phase is in 3 and shall slightly enhance rainfall.
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Summary

Monitoring


Weekly Monitoring:On the 11th, eastern region of Gampaha, western region of Kegalle and the south eastern sea near Hambantota received up to 90 mm rainfall while surrounding districts and eastern, southern, western sea regions received up to 30 mm rainfall. Up to 40 mm rainfall was seen only in south eastern sea are near Hambantota while the north east and eastern sea regions also received up to 30 mm rainfall. Eastern region of Kurunegala near Maho received up to 170 mm high rainfall while central region of Kurunegala, Dehiattakandiya and the sea east to Pottuvil received up to 90 mm rainfall on the 13th. The districts around Kurunegala received up to 40 mm rainfall on the same day. Up to 170 mm rainfall was seen in the sea near Pottuvil while Dehiattakandiya, Ampara and Batticaloa districts received up to 140 mm rainfall on the 14th. Up to 70 mm rainfall was seen in the entire country except northern region on the same day. On 15th May, Heavy rainfall was seen almost in the entire country. All the districts of northern province, Northern region of Anuradhapura, Trincomalee, all western region districts, Puttalam and sea west to western province received up to 200 mm rainfall while Kurunegala, Kegalle, Anuradhapura, Puttalam received up to 140 mm rainfall. Up to 90 mm rainfall was seen in other districts also on the 15th. Anuradhapura and surrounding districts and the northern sea region received up to 180 mm rainfall on 16th May while other districts also received up to 30 mm rainfall except southern region of the country. On 17th May, a significant reduction of the rainfall was seen in the entire country. Only Kurunegala town and Katana regions received high rainfall up to 90 mm, while central & western districts and the western sea of the country received up to 40 mm rainfall.


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

Predictions

14-day prediction:NOAA NCEP models predict up to 115mm total rainfall in south western region while up to 55 mm total rainfall shall receive in northern and eastern regions of the country during 18th – 24th and 25th- 31st May. Central regions of the country shall receive up to 65mm total rainfall during these two weeks.

IMD WRF Model Forecast & IRI forecast:According to the IMD WRF model, more than 125mm total rainfall shall have around Ratnapura while up to 65mm rainfall is expected in Colombo, Kalutara, Gampaha and Puttalam districts on the 19th. There shall be up to 125mm rainfall in Ratnapura and Kegalle districts while up to 65mm rainfall is expected in western region of the country on the 20th.The IRI CFS model predicts heavy rainfall around Galle while up to 200 mm total rainfall in Galle, Kalutara and up to 150 mm total rainfall in Colombo and Gampaha during 18th-23rd May.

Seasonal Prediction:As per IRI Multi Model Probability Forecast for June to August, 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 May 12, 2016 :During early 2016 the positive tropical Pacific SST anomaly was quickly weakening, now indicating only a weak El Niño. The atmospheric variables continue to support the El Niño pattern, but at much reduced strength. This includes just mildly weakened trade winds and excess rainfall in the central tropical Pacific, failing to extend eastward as it did in previous months. Most ENSO prediction models indicate a return to neutral by the end of May, with likely development of La Niña (of unknown strength) by fall.
INDIAN OCEAN STATE :1 degrees C above average sea surface temperature was observed around Sri Lanka.
MJO STATE :MJO phase is in 3 therefore shall slightly enhance rainfall in Sri Lanka.