Highlights: Dry conditions were mostly seen throughout the county in the previous week. The highest recorded rainfall in the week was on the 2nd which was less than 20 mm in the Northern regions of the country. As expected, the lowest temperature was recorded in Nuwara Eliya to be between 15- 20 OC while the maximum temperature was recorded from the North Eastern coastal belt to be between 35-40 OC. 0-1 OC above average temperature anomaly was experienced throughout the country. Up to 55 km/h north westerly wind was experienced in the lower half of the island. Considerably wet weather conditions are expected in the Northern province from 7th-13th September. Up to 35 mm of rainfall is expected close to Jaffna and Kilinochchi including the adjacent sea. Up to 55 km/h north westerly wind is expected in the southern part of the island.
Weekly Monitoring:On 1st of September North Western sea near the island received rainfall up to 30 mm while the South Western sea region received up to 20 mm rainfall. Up to 5 mm of rainfall was observed in Deraniyagala, Pussella and Kuruwita regions near the border of Kegalle and Ratnapura districts. On 2nd of September Pooneryn and Nallur regions received up to 20 mm of rainfall and on 3rd surrounding areas of Paranthan, Vettilakerni and Chundikulam received rainfall up to 10 mm. Rainfall less than 5 mm was observed in some parts of the Mannar district including Tantirimale and Mahawilachchiya areas in Anuradhapura district on the 4th. During the period 5th and 6th no rainfall was observed in any part of the country. For the past week, the RFE 2.0 tool shows rainfall between 10-25 mm in Pooneryn, Nallur, Paranthan, Chundikulam and Kilinochchi including Mankulam and Tantirimale areas. Similar amount of rainfall is shown in Kalutara district and some parts of the Galle, Ratnapura and Kegalle districts including Ruwnwella, Kithulgala, Madampe, Kalawana, Nelluwa and Elpitiya. It also shows below average rainfall of 25-50 mm in Gampaha and Colombo adjacent areas in the Western province and in some parts of Kegalle, Nuwara Eliya, Badulla, Galle and Matara districts. A below average rainfall of 10-25 mm is shown for all of the other central and southern regions of the island except for Embilipitiya and Hambegamuwa areas.
Monthly Monitoring: Rainfall for the month of August was considerably low compared to the month of July. Only district to receive an average rainfall exceeding 7 mm was Jaffna. The average rainfall in any of the other districts was below 4 mm. The rainfall in Jaffna was slightly above normal with a values of between 2-4 mm while that of the western and southern regions were 4-8 mm below normal. The average rainfall for the rest of the country was below 2-4 mm except for Mulaitivu and Kilinochchi.
For the period from 28th August to 3rd of September the lowest temperature was recorded in Nuwara Eliya to be between 15-20 OC. The maximum temperature was recorded in the North Eastern coastal belt to be between 35-40 OC. The maximum temperature of Kandy, Kegalle, Ratnapura, Badulla and Galle areas were 25-30 OC. During this period an above average temperature of 0-1 OC was observed in the entire country.
At 850 mb level 35-55 km/h north westerly wind was experienced by the southern half of the country while 30-35 km/h north westerly wind was experienced by the northern. At 700 mb level north westerly wind was experienced all over the country with speed less than 20 km/h.
Pacific seas state: September 8, 2016
During mid-August 2016 the tropical Pacific SST anomaly was close to -0.5C, approaching the weak La Niña threshold. However, most key atmospheric variables continue to indicate neutral ENSO conditions. Although the upper level winds in the tropical Pacific are slightly suggestive of La Niña, the lower level winds remain near average. The Southern Oscillation index and the pattern of cloudiness and rainfall in the equatorial Pacific also indicate neutral ENSO despite a mild tilt toward La Niña. The collection of ENSO prediction models indicate SSTs most likely near the borderline of cool-neutral and weak La Niña from the present through fall and into winter. (Text Courtesy IRI)
Indian Ocean State
0.5 OC above average sea surface temperature was observed in the north eastern sea of Sri Lanka.
14-day prediction: NOAA NCEP models predicts between 25-35 mm of rainfall in Jaffna and Kilinochchi and the adjacent Northern sea for the period from 7th– 13th September. For the same period up to 25 mm of rainfall are expected in Mannar, Vavuniya and Mulativu. Slightly enhanced rainfall conditions are expected in the Northern region of the island for the period from 14th-20th September. During that period up to 45 mm of rainfall is expected in the Jaffna district and the adjacent sea, up to 35 mm of rainfall is expected in Kilinochchi district and the adjacent sea and up to 25 mm of rainfall is expected in the Mullaitivu, Vavuniya and Mannar districts including surrounding regions of Ampara. For the same period between 5- 15 mm of rainfall is predicted for North Central, Central, Eastern provinces and for the Northern region of the Uva province.
Weekly prediction: IMD GFS model predicts rainfall up to 10 mm in Southern region of the Puttalam district and the adjacent sea on the 9th of September. On 10th rainfall up to 10 mm is expected in Kurunegala, Galle and Nuwara Eliya districts including the Western, Sabaragamu and Uva provinces. On 11th rainfall is expected to be increased with Batticaloa, Trincomalee and nearby regions also experiencing rainfall up to 10 mm. Also between 10-20 mm of rainfall is expected in Colombo, Kalutara and the adjacent sea regions. On 12th and 13th the Southern and Northern regions are expected receive rainfall up to 10 mm.
IMD WRF Model Forecast & IRI forecast:According to the IMD WRF model, for the period from 7th– 9th September up to 2.5 mm of total rainfall is expected in the coastal regions of Western and North Western provinces. The model predicts considerable increase in the rainfall on the 10th with Western province receiving rainfall up to 36 mm and the rest of the Western region of the island and the adjacent sea receiving up to 8 mm of rainfall. The IRI model predicts no extreme conditions for the coming week.
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.
NOAA CPC GFS model predicts 40-45 OC maximum temperature along the border of Eastern and Uva provinces. The maximum temperature of Colombo, Kalutara, Galle and Ratnapura areas will be between 25-30 OC while in Kandy, Matale, Puttalam, Kurunegala and Matara districts the maximum temperature will be between 30-35 OC. For the same period minimum temperature is expected in Nuwara Eliya, Kandy, Ratnapura and Badulla to be between 15-20 OC.
The 850 mb level predicts up to 54 km/h north westerly wind in the southern part of the country while up to 36 km/h south westerly wind is expected in the central region of the country and also in Puttalam and Anuradhapura areas. The 700 mb level predicts up to 36 km/h north westerly winds for southern regions and up to 20 km/h winds in the same direction for central regions of the country.
MJO based OLR predictions
MJO is weak and therefore shall not have an impact on rainfall in Sri Lanka.