Weekly Hydro-meteorological Report, 1, December 2016

Highlights:

•  The IMD WRF model predicts heavy rainfall (up to 125 mm) on 2nd December in the northern sea adjacent to the island.  
•  A Significant decrease in rainfall events was experienced throughout the island during 23–28 November, with the highest recorded rainfall of 60 mm on the 23rd in Mannampitiya region.
•  From 20-26 November, Minimum temperature of 15 ^OC was recorded from Nuwara Eliya district while most parts of the island recorded a maximum temperature between 30-35 ^OC.
•  From 22-28 November, up to 18 km/h north easterly winds were experienced in the northern and southern regions of the country while the central regions received up to 22 km/h wind in the same direction.

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Summary

Monitoring


Weekly Monitoring: On November 23rd surrounding areas of Mannampitiya received rainfall up to 60 mm; coastal areas of Puttalam and adjacent western sea received rainfall up to 30 mm; Talawa and Galnawa in Anuradhapura district, Siyambalanduwa in Monaragala district, Lahugala in Ampara district and Punani in Batticaloa district received rainfall up to 20 mm. No significant rainfalls were recorded on the 24th. On 25th Panadura and Kalawana regions received rainfall up to 20 mm; south eastern sea adjacent to the island received up to 120 mm rainfall. During 26th-28th no significant rainfalls were recorded in any part of the island; south eastern sea adjacent to the island received rainfall up 70 mm and 60 mm on 26th and 27th respectively. For the past week, the RFE 2.0 tool shows total rainfall up to 85 mm in Manampitiya region; up to 55 mm for Colombo, Kalutara, Galle, Matara, Monaragala, Talawa and Galnawa regions; and below average rainfall of 50-100 mm in most parts of the island.


Monthly Monitoring:Below average rainfall conditions were experienced in the entire island in the month of October except for coastal regions of Galle district, where monthly average rainfall amounted to 450 mm/month. Rainfall did not exceed 210 mm/month for the rest of the island. The CPC Unified Precipitation Analysis tool shows ~100 mm of total rainfall in Gampaha, Colombo, Ratnapura, Galle, Matara, Anuradhapura, Mannar, Vavuniya,, Matale, Kandy and Nuwara Eliya districts ; and ~25 mm of total rainfall in Ampara, Badulla, Monaragala, Kegalla and Jaffna districts.

Predictions

14-day prediction:From 30th November - 6th December, the NOAA NCEP models predicts total rainfall up to 55 mm for coastal regions of Colombo, Galle and Matara districts; 45-55 mm in Jaffna and Mullaitivu districts; 35-45 mm in Gampaha, Puttalam, Kilinochchi and Vavuniya districts. From 7th-13th December total rainfall between 85-95 mm is expected in Galle and Matara regions; 75-85 mm in Ratnapura; 45-55 mm in Colombo, Kegalla, Nuwara Eliya and Badulla regions.

IMD WRF Model Forecast & IRI forecast:: According to the IMD WRF model, more than 125 mm of rainfall is expected on the 2nd in the northern sea adjacent to the island. On the 3rd, up to 35 mm of rainfall in Gampaha, up to 7mm of rainfall in rest of the western region of the island; and a decreasing tendency of rainfall is expected throughout the country.

Seasonal Prediction:As per IRI Multi Model Probability Forecast for December to February 2017, the total 3-month precipitation shall be climatological for the whole island. 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 During mid-November 2016 the tropical Pacific SST anomaly was slightly cooler than -0.5C, the threshold for weak La Niña. Also, most of the atmospheric variables across the tropical Pacific have been consistent with weak La Niña conditions. The upper and lower atmospheric winds have been suggestive of a strengthened Walker circulation, and the cloudiness and rainfall have also been consistent with weak La Niña conditions. The collection of ENSO prediction models indicates SSTs near or slightly cooler than the threshold of La Niña during the remainder of fall, persisting through mid-winter, then weakening to cool-neutral by later winter.(Text Courtesy IRI)
INDIAN OCEAN STATE :0.5 ^OC above average sea surface temperature was observed in the southern sea of Sri Lanka.
MJO STATE :MJO shall enhance the rainfall in Sri Lanka during the next 5 days and shall suppress the rainfall for the following 10 days.