METEOROLOGY DIVISION MINISTRY OF CLIMATE CHANGE, ENERGY, DISASTER MANAGEMENT, METEOROLOGY, INFORMATION & COMMUNICATIONS. KINGDOM OF TONGA Climate Update for Tonga August Climate Summary Rainfall Outlook and Drought Update for October - December P.O. Box 845, Domestic Terminal, Fua amotu Airport, TONGA, Tel: (676) 35355/38 Fax: (676) 35123 Email: metstaff@met.gov.to Issued 11 th September August Climate in Brief CONSERVE WATER! Water conservation measures is recommended to be taken as much as possible across the country. The rainfall for August was very low in Tongatapu and below normal in Vavaú, Haápai and Niuafoou The rainfall outlook for the October to December period is for normal to below normal across the country. El Niño development remains possible during the coming months. Temperature Mean air temperatures were Above normal in the Niuafo ou and below normal for the rest of the country. The mean air temperature for the month recorded in Fua amotu was 21. o C which was. Daytime maximum and Night time minimum temperature were cooler than normal across the country. Cooler than normal night time temperatures are indicative features of El Niño. Table 1: Temperature August Mean Max Mean Min Mean Departure from Normal Highest Max Temp ( o C) Lowest Min Temp ( o C) Niuafo ou 29. 22.2 25.6.1 31.2 on Fri 2.4 on Tue 26th Above normal Niuatoputapu 28.1 22.8 25.5 -.3 29.9 on Mon 4th 2.5 on Tue 5th Vava u 25. 18.2 21.7-1.1 27. on Fri 12.5 on Sun 31st Ha apai 24.9 2. 22.4 -.7 26. on Fri 17. on Mon 18th Nuku alofa 25. 17.7 21.4-1.6 27.3 on Wed 6 th 13.6 on Thur 14th Fua amotu 24.1 18. 21. -.4 26.4 on Thu 21st 12.5 on Thur 14th
Page 2 METEOROLOGY DIVISION August Rainfall Rainfall for the month of August was below normal throughout the country except Niuatoputapu which was above normal. Table 2. Rainfall Totals for August Station (data period) Niuafo ou 1971-21 Niuatoputapu Vava u Ha apai Nuku alofa 1945-21 Fua amotu 198-21 Jun Jul Total August Highest daily Total Total Rainfall 33.4 11.7 37.1 6.1 on Mon 18th 28.3 125.2 148. 97. on Fri 8th 41.9 54.9 42.4 19.4 on Sun 1th 3.1 47.2 34.6 11. on Sat 144.3 157.7 15.3 8.8 on Sat 134.7 121.3 13.9 6.8 on Sat Rainfall >=.2 Rainfall >=1 mm Rainfall >=5 mm (mm 19 day Nil Nil 17 days 2 days 1 day Above normal 11 days 2 days Nil Below Normal 15 days 1 day Nil 8 days Nil Nil Extremely low 6 days Nil Nil Extremely low Forecast Verification for the last 3 months, June August. Table 3. June August The Rainfall prediction June to August was bias towards Above Normal for Tongatapu, Vavaú and Haápai and normal for the Niuas. The observed rainfall for the last three months was normal in Niuatoputapu and Nuku alofa and for the rest of the group. June - August 33%tile Rainfall Forecast Range 67%tile Rainfall June Aug Observed Data Niuafo ou 277.3 419. 88.2 Niuatoputapu 231. 352.1 31.5 Normal Vava u 254. 353. 139.2 Ha apai 191. 314. 111.9 Nuku alofa 24. 362.3 317.3 Normal Fua amotu 271.1 41. 269.9 Below Normal
Current Conditions Drought Update Rainfall in Haápai, Vavaú and Niua foóu have been below normal for the last three months (June to August). Rainfall recorded in Tongatapu in August was extremely low. The forecast for the next 3 months (October-December) is for normal to below normal across the country. With the current situation, and the Pacific Ocean showing remaining neutral levels, models suggest signs of El Nino development remains at 5% chance of occurring in the next few months, It is recommended that water conservation measures be taken as much as possible to the whole of Tonga. El Niño Southern Oscillation (ENSO) UPDATE Despite tropical Pacific Ocean temperatures remaining at neutral levels with little change in the last Seasonal Predictions for Tonga (October December ) Northern Tonga : There is little indication of bias towards either above normal, normal or below normal rainfall. Central Tonga: Southern Tonga: Normal to below normal. Normal to Above normal. The confidence level in the outlook is related to how consistently the Pacific Ocean affects the rainfall in Tonga. Therefore the outlook confidence level for the October to December period according to climatological historical data shows this effect to be good especially for Southern Tonga and central Tonga and low to northern Tonga. Table 4. Seasonal Rainfall Outlook for October to December. probability (%) 33%tile Rainfall Normal Probability % 66%tile Rainfall Above normal Probability (%) Niuafo ou 34 639 33 855 33 Niuatoutapu 34 533 35 747 31 Vava u 35 383 39 618 26 Ha apai 36 257 38 421 26 Nuku alofa 29 294 42 421 29 Fua amotu 17 39 44 435 39 :Note the rainfall values are for the three month period (Oct Dec ).
Monthly rainf all totals Temperature (deg C) Monthly Rainfall Totals Temperature ( o C) Monthly Rainfall Totals Temperature (oc) Rainfall Recorded over the last 13 months, August 213 to August Page 4 Fua'amotu Airport 35 3 25 2 15 1 5 Average Rainfall (1971-) Monthly Total Rainfall Monthly avg Max Temp Monthly avg Min Temp Lupepau'u Airport 35. 3. 25. 2. 15. 1. 5.. Average Rainfall (1971-) Monthly Total Rainfall Monthly avg Max Temp Monthly avg MinTemp Pilolevu Airport 35 3 25 2 15 1 5 Average Rainfall (1971-) Monthly Total Rainfall Monthly avg Max Tem Monthly avg Min Tem
Page 5 Note: Drought Update The Tonga Meteorological Service currently uses the Seasonal Climate Outlook for Pacific Island Countries (SCOPIC) Model for its seasonal rainfall prediction, validation and drought analysis. The system analyses current sea surface temperature patterns across the Pacific Ocean and then matches the most similar patterns experienced through the available historical period. The terms refers to rainfall in the lowest 33%, Normal refers to rainfall between the 33% and 67%, Above normal refers to rainfall in the highest 67%. Table 4 shows the percentage chance of receiving rainfall in each category from meteorological stations in Tonga. If conditions are Climatology then it means that we are forecasting an equal chance of rainfall to be in any tercile. Average day time and night time temperature is the average daily maximum and minimum temperature recorded throughout Tonga. The drought analysis summary is based on the ENSO phases on a 4 month aggregate drought index using the Decile method. The decile method (sometimes called the percentile method) is one of many types of drought indices used to help indicate and predict drought. SCOPIC uses the decile method to generate drought indices in its drought analyses. SCOPIC focuses mainly on meteorological drought as it uses only rainfall for analysis. Drought is a weatherrelated natural disaster that occurs when there is not enough water for users' normal needs. As people use water in many different ways, there is no universal definition. In this analysis we refer to drought as a prolonged period of below-normal rainfall (4-month rainfall that is below the 4th percentile. In this issue the use of Southern Tonga refers to Tongatapu and Eua, Central Tonga refers to Ha apai and Vava u, Northern Tonga is referred to Niuatoputapu and Niuafo ou. Disclaimer This summary is prepared as soon as possible following the end of the month, once climate data is received from recording stations around Tonga so the values may change on receipt of later information and the ENSO information is received from various Meteorological Agencies. Delays in data collection, communication and processing occasionally arise. While every effort is made to verify observational data, the Tonga Meteorological Service does not guarantee the accuracy and reliability of the analysis and rainfall predictions presented, and accepts no liability for any losses incurred through the use of this summary and its contents. This information should be used as for guidance only. All requests for data and for further information about this forecast should be directed to the Director of the Tonga Meteorological Service, at P.O. Box 845, Nuku alofa. Or email at metstaff@met.gov.to