by Roger Smith, Yachtmaster

PREFACE

The following  is not intended to be a detailed thesis on what causes “weather”,  nor on how to forecast it. Firstly I am not a meteorologist, and secondly there are very many excellent books available on the subject aimed specifically at mariners, written by Australian meteorologists for Australian conditions.

Weather-1Every cruising yacht should have one on board, and every skipper should at least be familiar with the basics. This will make a big difference in interpreting weather charts and forecasts and generally understanding the weather patterns. The Australian Government Bureau of Meteorology Marine Weather web site alone has a massive amount of information and relevant links, and well worth studying. In addition, most cruising guides (eg Alan Lucas's Cruising the NSW and Coral Coast) have a section on weather, and most yachting magazines from time to time run articles written by eminent meteorologists. Plus of course there is plenty of information available on the Internet.

Certainly the structure of the atmosphere and the movements of global weather systems are extremely complex and even today forecasting remains an inexact science. This article is based on experience gained over a period of more than 30 years of racing and cruising on the east coast, including 8 years spent delivering yachts, and describes the weather conditions likely to be encountered by yachts cruising between southern NSW waters and far north Queensland.


GENERAL

A cruising skipper looks at weather from a very different viewpoint to a racing skipper. The latter has no choice about when to put to sea – race starts are only rarely delayed for reasons of weather. The cruising skipper however has the luxury of deciding when to leave port and that decision will nearly always be dependent on the weather forecast. It is therefore important to know where and when the latest forecasts, both short term and longer term, can be obtained. Naturally, a skipper about to cross the Tasman, will be much more interested in the long term forecast than the skipper heading for a destination 50 miles away. Forecasts are usually obtained by the following means:

  • VHF Radio from Volunteer Marine Radio Stations (VMR's)
  • HF Radio from VMC in Charleville and VMR in Wiluna  (including weatherfax), or by email (ie Sailmail).
  • Mobile phone (subject to coverge) from any number of sources
  • Satellite phone from any number of sources
  • From the Internet, using a wireless or mobile phone connection (subject to coverage).

 


EAST COAST WEATHER PATTERNS

“Normal” Summer and Winter Patterns

Firstly, keep in mind that the weather frequently does not follow the “normal” patterns. Always be prepared for conditions which differ considerably from what “should” be happening.

In simplicity, east coast weather systems are a series of highs moving from west to east with fronts or troughs in between. In summer the centres of the highs are further south, usually around the latitude of Tasmania, and in winter they usually cross the continent on a latitude between Sydney and Brisbane. Cold fronts spin off from lows in the Southern Ocean and move up the east coast, more frequent and more severe in the winter, and usually petering out as they reach the NSW north coast, only occasionally reaching far into Queensland. Occasionally stronger fronts move up the east coast, known as “southerly busters”, particularly in summer. Troughs are shown on weather maps as dotted lines and are areas of low pressure, which can produce widely varied weather, ranging from cloud, rain and little wind, to violent thunderstorms and damaging winds. Treat them with caution.

Summer weather on the NSW coast is typified by several days of NE, with re-inforced seabreeezes, the wind then shifting to N and NW, often quite fresh, ahead of a southerly change (cold front), after which a gradual shift to SE and back to NE as the high moves into the Tasman. Further north, in the tropics the summer seabreeze is usually less strong with a E - SE tendency further north. In winter however, with the highs further north and the seabreeze effect diminished, NSW usually experiences varied winds, with the SE trade establishing itself as we move north into Queensland, and blowing consistently and often strongly for many days on end. The winter highs have a higher central pressure than in summer, sometimes as high as 1040  hPa.

From October onwards, the SE trades on the Queensland coast tend to ease, with an increased frequency of easterlies and northerlies, making October and November the months when most cruisers head south from north Queensland, thereby avoiding the approach of the wet season and risk of cyclones. However the weather doesn’t always follow the rules, and it is not uncommon to experience strong SE’s continuing to blow for a week at a time, making it difficult to progress southwards.

East Coast Lows

Apart from a cyclone, these can generate the most potentially dangerous weather the yachtsman can encounter. Remember the grounding of the bulk carrier “Pasha Bulka” at Newcastle in June 2007. East Coast Lows can occur at any time of the year, but are most prevalent during the winter months, with June and July statistically showing the highest frequencies. Some years there are only 3 or 4 in 12 months, other times there have been 3 or 4 in a month. The Bureau has become more skilled at forecasting them in recent years, and usually 2 or 3 days warning is given. These intense low pressure systems are usually associated with a trough which forms between two highs, and are often accompanied by an east coast kink in the isobars on the surface charts, with a high in the Tasman and another south or southwest of the kink. They often form off the north NSW coast and move slowly south before moving off towards NZ as they dissipate. They commonly produce winds in the order of 50 to 80 knots and seas of 5 metres or more.  In September 1995 a wave height of 13 metres was measured at Bondi, and at Sydney Heads average conditions were 5 metre waves and 50 knots.

To avoid confrontation with an East Coast Low the best advice is to check forecasts and weather charts regularly, and keep a watch on your barometer (make sure it is correctly calibrated). BE PATIENT! Another day or two in port can make the difference between a delightful passage and one fraught with discomfort or even danger. There are many sad, lonely sailors around who have turned off their womenfolk by leaving in or into poor conditions because of impatience or bravado.


HEADING NORTH, NSW NORTH COAST

There are different views on the best time to leave the southern/central NSW coast for a passage north, but really anytime from the end of March onwards is reasonable, when the Summer nor’easters have eased, are blowing less regularly and are replaced by an increasing  predominance of winds from the southerly sector. Weather-2In autumn, with a high sitting over the east of NSW, the winds are usually light sea breezes with calms or light land breezes at night.  It is considered by many that the best time to leave is the day after a front has gone through.  This has the advantage that you know how strong the change is and you have a tailwind to go north, with the likelihood of several days of settled weather before the next change. The forecasts will give you at least a couple of days warning of the next front and the preceding northerlies, so you can arrange to be safely in port, before repeating the cycle (it is not unusual for strong northerlies to blow before the front arrives). 

When sailing north, the effect of the southerly flowing East Australian Current will be felt. It is at its strongest well offshore, so it pays to hug the coast, where some positive benefit can sometimes be felt from eddies. Even so, it is hard to escape adverse current of up to 2-3 kts when passing major headlands like Smoky Cape and Cape Byron.


HEADING NORTH, QUEENSLAND COAST

Once north of about Mooloolaba or even Moreton Bay on the way up, from May through to September, it is not so much a matter of where the wind is from but how strong the SE breeze is.  This strength depends on the central pressure and position of the high pressure system down south. Typically, in the Whitsundays a high of 1020 hPa gives almost no wind or light sea breezes, 1030 will yield 15 to 20 knots and a 1038 high can give 30 to 35 knots.  The winds are generally a bit stronger to the north and less to the south.  In between the highs the wind eases, so in these areas a slowly falling barometer means nicer weather, often with light winds from the northerly sector.  It is relatively easy to pick what is happening and to time your passages to miss the worst strong winds.

A common feature of the trip north is a series of rain squalls that will overtake you from the south.  These will usually increase the wind strength by 5 to 15 knots as they pass, even if they are well out to sea.  They can be identified easily by eye or on radar. 

Once you get north of Port Bundaberg, until reaching the Shoalwater Bay area, you will be able to receive weather forecasts on VHF relayed from the Rockhampton Weather Office, known to all as Rockymet. These are the best forecasts on the coast, comprising the normal Bureau forcasts, a detailed local interpretation, reports from weather stations and the opportunity for vessels to provide feedback and ask questions of the forecaster.


HEADING SOUTH, QUEENSLAND COAST

In a “normal” year, northerlies traditionally begin to appear in the Whitsundays about the beginning of October although it can be earlier or later.  These come about as heat lows form inland and troughs develop between the highs.  The leading side of these troughs generates northerlies; ideal for heading south.  You need to plan to get into a nice all round anchorage before the axis of the trough passes the coast, in anticipation of a shift back to the south. In a normal year you could expect to experience about 50%/50% north winds/south winds from October onwards, however this can vary considerably from maybe 25%/75% to 75%/25% so there is no guarantee.

As summer approaches there is a tendency for the weather to become less settled, with increasing temperatures, humidity and thunderstorm activity. In particular the area south from about Hervey Bay is prone to significant and frequent thunderstorms, mostly in the late afternoons. These often produce heavy rain, lightning and winds up to 45 knots, and are not always accurately forecast. Fortunately the majority tend to follow the shoreline but they need watching, particularly when closing the coast or entering a port or anchorage in the late afternoon. 


HEADING SOUTH, NSW COAST

In the winter months the weather in NSW is a very mixed bag, with unpleasant weather and strong winds interspersed with quite long periods of fine, often calm weather. Occasional strong westerlies are also a feature of this period. Changeable weather continues through spring, with a predominance of winds between S and NE as the summer cycle of NE seabreeze, followed by southerly change, shifting SE, then back to NE gradually becomes more frequent.

For yachts heading south from October onwards, it is a question of making maximum use of favourable winds when they occur and at the same time watching out for troughs approaching from the west, cold fronts moving up the coast from the south and the increasing likelihood of thunderstorms. A good scheme is to set out on the back edge of a high with a wide trough behind it.  It is then important to make port before the axis of the trough passes the coast or before the next front comes up from the south.  As in Queensland, there is an increase in the frequency of thunderstorms, continuing right through the summer months.

Heading south down the NSW coast, the East Australian Current is usually a reliable means of adding up to 2-3 kts to your speed over the ground. (See article elsewhere on this site). It is strongest out towards the 200 metre depth contour near the edge of the continental shelf, but it is not always necessary to go that far. In practise, having cleared the reefs off Danger Point on the NSW/Qld border, if a course is maintained to pass about 10 miles off Cape Byron, the current will usually be found. Staying that distance offshore will normally keep you in the current until at least Crowdy Head, south of Camden Haven. From there the current usually moves offshore and if your destination is Sydney it seldom pays to go further offshore searching for the current, and a direct course to your destination is best. If heading for the NSW South coast, the current moves closer to the coast south of Sydney, and it will usually pay to go in search of it (it often plays a key role in Sydney to Hobart race strategies).


Useful Weather links:

Australian Government Bureau of Metoerology Marine Weather

Alan Lucas's Cruising the NSW and Coral Coast

SeaBreeze Live Weather and Forecasts

Elders Weather Forecasts

This web site - Links Page

Buoyweather


Prepared by Roger Smith, Yachtmaster, CCCA member and Port Officer for Forster-Tuncurry December, 2008

See Also Members Only Feature Article "Experiences of a Yacht Delivery Skipper" by Roger Smith

See Also  "Where to Get Weather Forecasts" by Roger Smith