12-Month Rainfall Forecast
North Coast & Tableland 12-month Rainfall Forecast
Rainfall deciles10Well above normal8 - 9Above normal4 - 7Near normal2 - 3Below normal1Well below normal
Issue NotesIssued 5 Feb 2021
ENSO status: La Niña IOD status: Neutral SAM status: Positive La Niña is likely at its peak which has brought long periods of cloud and rain to eastern and northern Australia.The majority of models predict that La Niña will continue through February, with 3 of 8 predicting to March and most of the models indicating a return to neutral conditions (neither El Niño nor La Niña) in April. Neutral conditions are predicted to continue into the Australian winter. La Nina typically brings above normal rainfall across much of Australia. While La Niña is expected to weaken, above normal rainfall and typical La Niña impacts are still expected. La Niña typically favours periods of positive SAM, which can increase the amount of precipitation along the eastern half of the country, due to prevailing onshore winds. During summer, much of the country is likely to remain wetter than normal, however normal rainfall is expected for western TAS. La Niña typically increases the number of cyclones and brought anearly start to the wet season. During Autumn, many parts of Australia are likely to be wetter than normal, due to warmer waters off the northeast coast of Australia. Southern parts of SA, VIC and most of TAS are likely to observe normal precipitation for the time of year.Forecast Explanation
Notes on the concept of deciles
If all the data in a record are ranked from lowest to highest they can then be divided into 100 equal blocks. These blocks are known as percentiles. The values that fall into the lowest 10% range (from 0 to 10%) are said to be in the first decile, those in the group 10+% to 20% are in the second decile, and so on. Those in the group 90+% to the maximum value recorded are in the 10th decile. The 50% value is a special one known as the 'median'. It is noteworthy since there is the same number of records above and below its value.
Deciles have been found to be very useful for analysing rainfall in particular as its distribution is not the normal bell-shape distribution but is skewed towards many low values with only a few high values. The deciles can be described in qualitative terms. A table is provided in the accompanying results.