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VISIBILITY
The visibility in Sydney varies dramatically, from site to site and from day to day and month to month. It has always been common knowledge that the better visibility was generally in the colder months and the worst in Summer.
In May 2009 I analysed my dive log for the past 20 plus years and can report that based on the 1,758 dives I had done in Sydney at that time, the following is what I found:
The visibility does not seem to follow any real pattern apart from what I have stated above. I know that after some periods of huge seas when you would think the visibility would be poor it can be excellent. The opposite also applies, in that after a period of no rain and calm seas it can be terrible. The visibility (at least outside the harbours and bays) is more dependent on the ocean currents.
One thing that I have noticed, is that after a period of southerly winds we can get very good visibility. This is related to the Coriolis Effect. This is explained in detail at < http://en.wikipedia.org/wiki/Coriolis_effect>. Simply put, one of the effects of the Coriolis Effect is to causes cyclones to rotate clockwise in the southern hemisphere and anti-clockwise in the northern hemisphere.
In relation to oceans, a part of this phenomenon is the Coriolis acceleration (Coriolis force) which states that the actual flow of water is perpendicular to the flow of wind. Thus, off Sydney (and New South Wales), a southerly wind tends to push the surface water out to the east (towards the centre of the Pacific Ocean). In turn, the displaced water is replaced by cleaner water from deeper in the ocean.
In Winter, when westerly and north-westerly winds are prevalent in Sydney, the water is pushed south and warmer and cleaner water from the northern tropical areas is pushed closer to shore.
A summary of the visibility I have recorded is as below. For the purposes of this comparison, the following table relates the terms I use in my log book to actual visibility in metres.
Shithouse - less than 2 m
Very Poor - 2 to 4 m
Poor - 4 to 6 m
Fair - 7 to 10 m
Good - 10 to 15 m
Very Good - 15 to 24 m
Excellent - 25 to 30 m
Very Excellent - 30 m+
| Month | Very good
or better | Fair to Good | Poor or less | Good or better | % Waves less
than 1 m | % Waves less
than 1.5 m | % Waves more
than 2 m |
| January | 19% | 54% | 22% | 22% | 11.8% | 53.7% | 17.5% |
| February | 18% | 58% | 20% | 47% | 10.0% | 49.8% | 17.5% |
| March | 18% | 55% | 21% | 43% | 9.2% | 48.4% | 21.9% |
| April | 16% | 66% | 15% | 53% | 14.0% | 51.5% | 25.1% |
| May | 23% | 59% | 14% | 60% | 19.4% | 48.8% | 28.8% |
| June | 29% | 60% | 9% | 61% | 21.6% | 49.8% | 28.9% |
| July | 23% | 67% | 8% | 60% | 20.6% | 52.8% | 26.3% |
| August | 23% | 64% | 13% | 61% | 23.8% | 58.6% | 20.6% |
| September | 16% | 68% | 10% | 57% | 19.5% | 57.8% | 19.3% |
| October | 8% | 56% | 28% | 34% | 14.8% | 54.3% | 19.3% |
| November | 7% | 67% | 24% | 31% | 14.4% | 54.9% | 20.1% |
| December | 21% | 52% | 20% | 46% | 16.5% | 55.6% | 18.5% |
Notes:
As you can see, the period from April to September has better than average visibility, with May to August almost constantly the same percentage of 60% of dives having visibility better than 10 metres. The best month is easily June with 29% of dives having visibility of better than 15 metres. Close behind are May, July and August with 23%. June and July have only about 8% of dives with visibility of less than 7 metres. The months with the highest percentage of dives with visibility over 25 metres are July and August with over 6%.
April and September have a lower percentage of dives with visibility over 15 metres but a very high percentage of dives in the 7 to 15 metre range.
Poor visibility is definitely more common in October and November, with 24 to 28% of dives having less than 7 metres. These months also have virtually no visibility better than 25 metres (0.8% or 1 solitary dive). Opposing this, June and July have less than 10% of dives with this sort of visibility and April, May, August and September having about 10 to 15%.
As you can see from the above records of my dives over the past 20 plus years, the visibility in Sydney is by far better in the Winter period, with the June to August period being exceptional and May and September close behind. December, February and March are not too bad but October, November and January are a lot worse.
WAVE HEIGHTS
Also included in the above table is some information about wave heights in Sydney. This comes from data recorded over almost 20 years till October 2012 by the Manly Hydraulics Laboratory's wave recording bouy. This is located off the northern beaches. The statistics seem to be calculated on data capture once an hour over this period, with almost 90% of the waves recorded.
Form this, you can see that October to April has the least calm seas, with January to March being the worst for this. Conversely, May to September has the best chance of days with waves udner a metre. August appears to have the overall flattest seas, with almost 60% being under 1.5 metres.
Even though winter (and either side of winter) has the flattest seas, it also contains the roughest seas. May and June have by far the largest percentage of seas over 2 metres at almost 30%.
WATER TEMPERATURES
Since I started diving in 1988 I have kept accurate records of the water (and air) temperature for all my dives. Before 1994 the temperature was recorded on an analogue gauge (shown without decimals) but since then it is from my various dive computers (with decimal point). In June 2013 I analysed the data and found the following which comes from over 2,200 dives.
| Month | Min ÂșC | Max ÂșC | Av ÂșC | Standard deviation
Min ÂșC | Standard deviation
Max ÂșC |
| January | 11.7 | 24 | 18.7 | 16.4 | 21.1 |
| February | 13 | 24.4 | 19.3 | 16.8 | 21.8 |
| March | 14 | 24 | 19.7 | 17.7 | 21.7 |
| April | 14.5 | 22.7 | 19.7 | 18.4 | 21.0 |
| May | 15.2 | 23.6 | 18.8 | 17.5 | 20.1 |
| June | 12.7 | 20 | 17.0 | 15.7 | 18.2 |
| July | 12 | 19 | 16.0 | 14.9 | 17.0 |
| August | 13 | 18 | 15.7 | 14.6 | 16.7 |
| September | 13.5 | 18 | 15.7 | 14.8 | 16.7 |
| October | 11.5 | 19.2 | 16.0 | 14.6 | 17.3 |
| November | 13.5 | 24 | 16.9 | 15.2 | 18.6 |
| December | 13.2 | 22.5 | 18.1 | 16.0 | 20.2 |
| Overall | 11.5 | 24.4 | 17.8 | 15.5 | 20.0 |
As can be seen from this table, based on averages, the warmest water in Sydney is in March and April and the coldest in August and September. In some cases, the minimum temperatures were recorded on deep dives (over 40 metres) and was only at depth. However, in a lot of cases we have had very cold water even when doing shore dives.
However, when standard deviations are taken into account (basically dropping off some of the lowest and highest temperatures), the coldest months are August and October with September not far behind. The warmest is February with March close behind. This probably gives a better idea of the sort of temperatures that are experienced on most dives.
Summary:
Based on both visibility and sea conditions, winter is a great time to dive in Sydney. In order, I would say that August, July and June are the best months for conditions. This tallies with my gut feelings over the years.
Get out there and experience winter.
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