Mid North 12-month Rainfall Forecast

10 5 0
Jul 18
4
Aug 18
5
Sep 18
5
Oct 18
7
Nov 18
5
Dec 18
9
Jan 19
8
Feb 19
7
Mar 19
8
Apr 19
6
May 19
4
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: Neutral
Indian Ocean Dipole (IOD): Neutral

Sea surface temperatures (SSTs) and atmospheric indicators across the equatorial Pacific Ocean remain within neutral values.

The Nino3.4 index dropped to 0 in May for the first time since August 2017. On the other hand, the Southern Oscillation Index (SOI) recorded a value of 2.1 in May.

Current consensus suggest neutral ENSO conditions through the southern hemisphere winter. Long range forecasts continue to hint at the possibility of an El Nino event towards the end of 2018, though only three out of eight international models reach El Nino thresholds by the end of the year.

Warmer than average sea surface temperatures (SST) remain across the eastern seaboard as well off South Australia and Tasmania. These, however, have experienced some cooling since the end of summer.

Climate forecasts favour average-to-below average rainfall for most of Australia's southern half in June, with below average rainfall likely to persist across the eastern states through to August. Warm SSTs off the eastern seaboard could bring some relief rainfall east of the ranges across NSW and eastern Victoria, most likely through intense weather events.

Due to the lack of rainfall through the first half of 2018 most of NSW, far north western Victoria and southeastern SA, 5-month rainfall deficiencies remain at serious-to-severe deficiency levels.

In the longer term, there risk for a possible El Nino-like conditions during the second half of 2018, could favour a drier than average outlook for the eastern half of the country through spring.

Issued Jun 12

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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