Central Coast 12-month Rainfall Forecast

10 5 0
No forecast available for this district.
Rainfall deciles
10 Well above normal
8-9 Above normal
4-7 Near normal
2-3 Below normal
1 Well below normal

Issue Notes

ENSO status: El Niņo, reduced atmospheric effect.
IOD status: Neutral, Positive IOD ended.
SAM status: Positive, trending neutral.

The El Niņo Southern Oscillation (ENSO) is in an El Niņo, with all international models indicating this event will continue until about April 2024. Ocean warming has peaked over the central Pacific. The Southern Oscillation Index (SOI) is close to zero over the last 30-60 days, showing that the atmosphere is not reflecting the ocean components. Therefore, Australia is feeling reduced effects from this El Niņo event. El Niņo only has a limited effect on rainfall during summer, typically drying Far North Qld, increasing rainfall over the Nullarbor, and having little effect elsewhere. El Niņo events can make southern Australia slightly drier than normal during Autumn.

The Indian Ocean Dipole (IOD) is now back into a neutral phase, after a much later than normal finish to 2023's positive event. Oceans are remaining high near the Horn of Africa, put warming has also occurred near Jakarta. The IOD will likely stay neutral during Autumn, with low confidence of either a positive or negative phase.

The Southern Annular Mode (SAM) is currently weakly positive but will be mostly neutral in February and early March. A positive SAM increases easterly winds more likely, increasing rainfall and thunderstorm activity in the east, but reducing it in southern and Western Australia.

Rainfall outlooks are predicting mostly drier than normal conditions across Australia during February, likely due to a monsoon retreat. Conditions are forecast to be similiar in March (although another monsoon onset would lead to wetter conditons in the north) while average conditions throughout are expected in April and May.

Issued Feb 6

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.

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