We thought we would include a page on the weather with a few brief explanations to help with planning the best dive for the day off the coast. When diving the wrecks or planning a trip it's important to assess the weather for both safety and conditions on the wreck sites. No two wreck sites are the same for diving conditions and each wreck is a little bit different in topography, depth and accessibility. We've kept best weather conditions for each site description brief, in almost all descriptions we give only the maximum amount of swell that we would describe each site being not only enjoyable but safe. It's important that anybody using the site uses their own judgement in deciding for themselves what is safe and what is beyond their capabilities.
Generally the rule of thumb for being on the ocean in WA is the rule of 15, being that swell under 1.5 metres and wind under 15 knots is an enjoyable day on the water however, everybody or every boat is different and has different capabilities.
Having a website that covers the far north to the south coast, we provide links for checking what we think are the biggest influences on diving for a particular area of the state. For example, the Kimberley region we included links to the wind forecast and tide tables but not wave data. The Kimberley rarely experiences swell over 1 metre however, it is subject to the second largest tides on the planet with currents reaching up to 5-8 knots. On the other hand, tide has almost no influence on diving south of Kalbarri with swell being the major influence south of North West Cape. That is why the sites south from the Midwest section only have links to wind and swell. Although we provide the few links we've found the most beneficial, every resource available should be used to give the best picture of the weather conditions through other weather sites and sources available for the dive area.
The main links we've included are the weather pages we use commercially and recreationally. The main source for a weather forecast is the new state of the art forecasting and weather modelling site from the Bureau of Meteorology called Meteye. Meteye was launched about three years ago by the BOM and has always been the most accurate forecasting tool we've experienced, it is fantastic and especially accurate when travelling to remote places that other weather sites do not cover. We have linked Meteye for wind and swell forecasts and although we do not hold much faith in Seabreeze forecasting we included links to Seabreeze for the real time wind data it displays when scrolling down the page. This included with the Department of Transports "Near Real Time Tide and Wave Data" link provide a valuable resource for last minute checking of conditions when leaving the house on the day of the dive.
As well as the links provided, below is our take on what to be aware of with weather and things to assess when choosing a site to dive.
SEAS/WAVES - Waves and swell are often confused. Waves are a localised effect on the sea state generated by the wind. These wind generated waves or seas are what are referred to as chop once they start to break and create white caps. Seas are created from the strength and distance that wind travels across the water's surface whipping up the waves, the further the distance wind has travelled across the water's surface the larger the seas. The amount of distance the wind has travelled across the water surface is referred to as "fetch" ie. the fetch of the wind. Waves only really affect surface conditions and do not pose much interference when diving offshore but they are what makes travelling to the dive site, safe anchoring and entry to the water difficult. When diving from shore, a wind direction with enough "fetch" to create waves that crash on to a beach will stir up shore sites and make for a poor dive, on most beaches in WA this would be the south westerly sea breeze.
SWELL - Different to waves, swells are larger, smoother, rolling waves with a much longer wave length between peak to peak amplitude. They are created far offshore from weather events and storms out in the Indian Ocean. Swell in WA travels for thousands of kilometres usually from the west south west and is relatively safe until it reaches shallow water where it stands up and forms into large breaking waves. Swell is what surfers ride, what creates surge under water and what sinks boats when they are in shallow water and at the wrong place at the wrong time. Swell is included in the site descriptions as it is the most important factor underwater in relation to diving. Swell is the motion of the ocean and what creates the suck and push of the surge that divers experience. Unlike seas that influence the surface, swell reaches the depths and stirs up the seafloor and swell heights and swell periods can be used to directly draw conclusions on the likelihood of visibility and the strength of surge rendering a site un-diveable. Swell is also important at shallow sites as swell can form large breaking waves. Please read the section on using our GPS marks, in order to accurately mark the wrecks, many of our marks can be dangerous depending on the swell. GPS marks show the location of a shipwreck and do not indicate a safe anchorage.
WIND - We don't include "best" wind conditions in the site descriptions and rather have this section as an explanation for wind. When assessing the conditions for heading out to a wreck, the location of the wreck in relation to the wind strength and wind direction need to be assessed. Wind will rarely affect dive conditions underwater on most sites unless diving from the shore. When diving offshore it does however dictate the accessibility of a site and safety in anchoring and entry and exit from the water. This is up to individual divers and the skipper to assess to their own capabilities. Wind is important in regards to the creation of seas and waves and the effect of "fetch" that is described in the waves section. Rather than describe wind directions for the entire state in detail it is probably best to use the terms onshore wind, offshore wind and fetch. Onshore wind is a wind direction that blows on to the shore coming from the ocean and offshore wind blows off the land out to sea. Generally wind over 10 knots will start to create small waves, over 15 knots white caps start to form. The further the wind has travelled across the ocean's surface to reach a site will determine the height of the sea state over a dive site. An example would be a 20 knot easterly wind on a Perth beach (offshore wind) with no swell. If you were to shore dive in Perth in 20 knots from the east, the beach would most likely be flat and surface conditions calm as the wind has no fetch, but take your boat out in a 20 knot easterly and a mile offshore things would get uncomfortable and by the time you're at Rottnest with 10 miles of fetch creating large seas, surface conditions would be very poor and best to seek a sheltered bay relative to the wind direction where the wind has no fetch. On the other side is the south westerly sea breeze over 20 knots (onshore wind), with the fetch coming from far out to sea over a very long distance this creates large waves and seas that crash right onto the shore line, unless diving in a sheltered island bay almost all dive sites will be too uncomfortable to enter the water, whether shore based or offshore.
TIDE - We've included tidal information links to the Swan River, Exmouth and Kimberley sections on the website. Usually off the Mid West, Perth and south coast tidal flow has little affect on diving due to the very small tidal range of less than a metre. Unlike the suck and push of surge experienced from swell, diving with a tidal flow is best described as current; a constant, one directional flow of water. If diving an area known for currents, it can be best to dive during neap tides that occur fortnightly with the first and third quarter moon phases and also diving the slack water during tide changes. This is certainly the case when diving in the Kimberley where currents up to 5 knots can be experienced. The Swan River provides a great site away from ocean swells and protected from most winds but it can experience currents in the areas of the dive sites in the lower reaches. The river from Mosman Bay to Fremantle creates a tidal pinch for the larger upstream water bodies of the Melville Water, Canning River and upper reaches of the Swan and stronger currents can be expected during fortnightly spring tides (full moon and new moon). Spring tides do not necessarily render the river un-divable but can affect visibility and will increase current strength. If planned well, a tide change can be exploited if long swims are expected to assist swimming to and from the site to the entry point. Lastly, Exmouth and further north, tides should be part of the mix in planning dives. Dangerous currents can be experienced at North West Cape and over the site of the Mildura where swell and tide meet. Many of the sites off Ningaloo Station sit wrecked on the outside up against the reef surrounded by shallow bommies and are exposed to swell. When diving around shallow bommies or reef areas it can at times be safer to dive the top of the spring tides to create more depth for the swell over shallow areas reducing the risk of breaking waves forming. It is also safer to run the many unmarked gaps in the Ningaloo reef on an incoming flood tide. If the swell is up and opposing the force of the outgoing ebb tide flushing out of the lagoon it can cause the swell to stand and break where it was not breaking an hour earlier, this has been the cause of boating fatalities almost every other year.
Hopefully the information above provides some use to anyone wanting to go out and enjoy the dive sites listed on the page. The intention was to keep it much more brief but I hope it is useful.