Hunter 12-month Rainfall Forecast

10 5 0
Oct 17
Nov 17
Dec 17
Jan 18
Feb 18
Mar 18
Apr 18
May 18
Jun 18
Jul 18
Aug 18
Sep 18
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 ENSO boundaries.

The Nino3.4 value decreased to -0.3 in August. The Southern Oscillation Index (SOI) recorded a value of 6.9 during the same month.

Current consensus continues to suggests La Nina side of neutral is likely during the remainder of the year. All eight international models are now indicating a cooler side of neutral (La Nina) by throughout the Austral summer, with four models reaching La Nina thresholds in December.

Sea Surface Temperatures (SSTs) across the far eastern Indian Ocean remain cooler than average,however, water over the NW Shelf have experienced some warming and are within their normal parameters for this time of the year. The current SST pattern in the Indian Ocean suggest a Positive Indian Ocean Dipole (IOD) event, which tends to bring below average rainfall to central and southeastern Australia during the tail end of winter and first half of spring. However, this pattern is gradually easing.

Climate forecasts are favouring average-to-above average rainfall for most of central and eastern Australia during October. Below average rainfall is however, favoured for eastern and southern Australia towards the end of spring. Further ahead, odds continue to favour average-to-wetter than average rainfall for parts of eastern Australia during summer, more so if we do end up experiencing a weak La Nina.

Warmer than average sea surface temperatures across northern and eastern Australia continue to increase the risk of an earlier onset of the wet season across Australia‚??s tropical north coast. Along the eastern seaboard, warmer than average SSTs could lead to intense but localised rainfall events later in spring and early summer. During neutral ENSO years, SE Qld and NE NSW tend to see above average thunderstorm activity during the warmer months.

Issued Oct 18

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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Rain on the way for NSW

14:59 AEDT A band of rain and thunderstorms will sweep across NSW at the end of this week, delivering the best falls in 4-5 months for some areas.

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