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Friday, September 30, 2016

Weekly Hydro-meteorological Report, 29, September 2016

Highlights: Dry weather conditions were experienced throughout the island during the previous week from 20th-26th September. Less than 10 mm rainfall was received by Ratnapura and Trincomalee regions. The minimum temperature of 20 OC was recorded from Nuwara Eliya district while the maximum temperature was recorded from the Northern and Eastern coastal areas to be between 35-40 OC. Up to 55 km/h north westerly winds were recorded in the southern regions of the country. For the period from 27th September - 11th October the NOAA NCEP model predicts dry weather conditions in the island. Up to 35 km/h north westerly wind is expected in the southern and western parts of the country. ENSO is still in the neutral phase and therefore shall not support rainfall conditions in Sri Lanka. MJO shall also suppress rainfall in the country in the next two weeks. Therefore the weather has a higher tendency to be dry over the next month.
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Weekly Monitoring:On 20th September Amarivaya of Tricomalee district and the adjacent sea region received up to 10 mm rainfall. On 21st north eastern sea near the island received rainfall up to 20 mm. No significant amount of rainfall was observed during the period 22nd - 25th in any part of the country. On 26th Pussella, Kuruwita and Kiriella regions of Ratnapura district received up to 10 mm rainfall. Rest of the Ratnapura district, Kalutara district and several regions of Galle, Colombo, Gampaha, Kandy and Nuwara Eliya districts received rainfall up to 5 mm. For the past week, the RFE 2.0 tool shows rainfall up to 25 mm for surrounding areas of Ratnapura, Kalawana, Kuruwita and Awissawella. Rainfall between 10-25 mm was received in Colombo and Kalutara districts including the adjacent sea region. The same amount of rainfall was received by neighboring regions of Pitigala and Nelluwa of Galle district, Moragoda and Balangoda of Ratnapura district and Radawana of Gampaha district. A below average rainfall of 25-50 mm is shown for Western province including districts Galle, Matara, Kegalle, Matale, Batticaloa, Badulla and several areas of Kurunegala, Kandy, Nuwara Eliya, Polonnaruwa and Monaragala districts. It also shows a below average rainfall of 10-25 mm for the rest of the island.

Monthly Monitoring: Below average rainfall conditions were experienced in the entire island in the month of August except in Jaffna. Monthly average amount to 7 mm/day in Jaffna peninsula and Ratnapura town while everywhere else the rainfall did not exceed 5 mm/day. The CPC Unified Precipitation Analysis tool shows ~75 mm of total rainfall in Jaffna, ~50 mm of rainfall in Kilinochchi, Ratnapura and Matara areas.

During the period from 18th-24th September the lowest temperature of 15-20 OC was recorded in Nuwara Eliya. The maximum temperature to be recorded was between 35-40 OC in the northern and eastern coastal belt including Monaragala and Polonnaruwa districts. The maximum temperature of Kandy, Kegalla, Ratanapura and Galle areas was 25-30 OC. The maximum temperature of rest of the country was between 30-35 OC. During this period an above average temperature of 0-3 OC was observed by the entire island except for the coastal regions of Puttalam and Mannar districts where an above average temperature of 0-1 OC was observed.
At 850 mb level 35-55 km/h north westerly wind was experienced by the southern part of the country while northern region experienced 30-35 km/h wind in the same direction. At 700 mb level entire Island experienced north westerly wind with 30-35 km/h speed.

Ocean State
Pacific seas state: September 15, 2016
During mid-September 2016 the tropical Pacific SST anomaly was close to -0.5C, the weak La Niña threshold. However, not all of the atmospheric variables support weak La Niña conditions. Although the upper level winds in the tropical Pacific are somewhat 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 are somewhat suggestive of weak La Niña conditions, but could also be interpreted as being in the cool-neutral range. The collection of ENSO prediction models indicates SSTs hovering at levels near borderline La Niña during fall, then weakening to cool-neutral in late fall and into winter.(Text Courtesy IRI)

Indian Ocean State
0.5 OC below average sea surface temperature was observed in the western and southern sea of Sri Lanka


14-day prediction: NOAA NCEP models predicts no rainfall in any part of the island during 28th September to 11th October.

Weekly predictionIMD GFS model predicts rainfall between 20 - 40 mm in western province and adjacent sea while it expects 10 - 20 mm rainfall for Kurunegala, Kegalla, Rathnapura and Elpitiya, Deniyaya of southern province and adjacent sea on 29th of September. And also North Western, central and southern provinces and adjacent sea area expects rainfall up to 10 mm. On 30th September Galle district and adjacent sea expects between 20 -40 mm rainfall while Matara, Rathnapura and western province expects between 10 -20 mm rainfall. Also up to 10mm rainfall in Kurunagala, Matale, Kandy, Kegalle, Puttalam, Tangalle, Ambalanthota and adjacent sea area. On 1st of October expects up to 10 mm rainfall in lower part of country including southern, Sabaragamuwa, Western, Uva provinces and Kurunegala, Monaragala, Mathale, Kandy. South western region of the island and the adjacent sea area is expected to revive up to 10 mm rainfall on 2nd October. On 3rd of October expected to revive up to 10 mm rainfall in Nuwara Eliya, Ampara, Monaragala, Badulla, Rathnapura and Western province. Except the north western region of the island other regions and the adjacent sea area is expected to revive up to 10 mm rainfall on 4th and 5th October.

IMD WRF Model Forecast & IRI forecast:According to the IMD WRF model up to 65 mm of rainfall is expected near Galle on 30th. while the rest of south western and western regions of the country shall receive up to 35 mm rain. On 1st south western regions shall receive rainfall up to 35 mm. IRI CFS model does not predict heavy rainfall during 28th September- 3rd October.

 Seasonal Prediction:As per IRI Multi Model Probability Forecast for October to December, the total 3-month precipitation shall be climatological in the northern half of the island. However, the southern half of the island has 30-40% likelihood of being in the below-normal tercile. 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 in the areas along the border of Eastern and Uva provinces. The maximum temperature along the coastal belt in the Northern and Eastern sides of the country and in Vavuniya, Polonnaruwa and Monaragala districts will be between 35-40 OC. The maximum temperature of Galle, Colombo, Kalutara 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 to be between 15-20 OC.

The 850 mb level predicts up to 35 km/h north westerly wind in the southern half of the country including North Eastern province. Up to 20 km/h south westerly wind is expected for the rest of the island. The 700 mb level predicts up to 28 km/h north westerly wind for the Southern province. Rest of the island is expected to receive westerly wind with speed less than 20 km/h.

MJO based OLR predictions
MJO shall not have a significant impact on the rainfall in Sri Lanka in the next 5 days and shall slightly suppress rainfall during the following 10 days.

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