Interpretation of the score (here the latest)

• Meaning: the scores represent the expected water movement at site entry/exit according to the forecasted swell and wind. It is not an indication of underwater visibility

• Purpose: help divers to choose a site on a given day and time.

• Disclaimer: actual conditions needs to be assessed on site by divers, the author takes no responsibility for any consequence arising from relying on this prediction. Actual conditions may differ due to prediction model tuning and intrinsic limitations (see bottom of the page).
  The model leverages forecasts by NSW Nearshore Wave Forecast and MetEye.

DESCRIPTION OF THE MODEL

• How does it work: based on the vulnerability of each site to swell, wave, tide and wind, a model has been made into a spreadsheet. Upon entering that forecasted data the graph show the dive-ability. The dive-ability takes into account site-specific factors, for example Fairlight is more sensitive to swell as even a small one can make you bump against the shallow reef access (hence it will have a higher penalisation compared to Camp Cove even when both are affected by the same local swell). 

• Which variables are considered by the model:

  1. Primary swell

  2. Secondary swell

  3. Wind wave

  4. Wind

  5. Tide

  6. Swell refraction

• How is the swell taken into account: for a given day and time in the future, primary swell, secondary swell and wind wave forecasts are used to calculate the wave power (height*height*period). Then the formulas calculate how much power reaches each site, on the basis of the  vulnerability parameters that have been defined for each site and for each direction of the swell. Refraction around headlands is also (empirically) taken into account.

• What about the tide: for some sites such as Bare Island, The Steps and Cabbage Tree Bay high tide worsen the protection from swell.

• What about the wind: in enclosed waters such as the Harbour or Botany Bay, wind chop can impact diving. Similarly to the swell, each site has a lobe of vulnerability to wind chop. Wind speed has an impact on wave energy (power of 2). Strong wind coming from land and contrasting the swell is also taken into account.

• All the factors above contribute to four types of "demerit points"  (tide, wind, swell and refraction), the total of which is deducted from a starting value of 60 points.

• How precise is it: after entering good sense parameters to start with, the model is fine tuned by testing it against reported dive-ability (ease of entry/exit, surge). The result is also obviously dependent on the accuracy of the weather forecast.

• Known limitations: the model is based on parameters and coefficients that are being tuned by matching actual conditions reported by the buoys and subjective assessment reported by the divers.

• Credits: the tool has been developed by Marco Bordieri from an idea of Scott Joseph.

• Contacts: Marco Bordieri via Facebook Messenger or email

SITE BY SITE DESCRIPTION

• CTB (Cabbage Tree Bay): the score represents the water movement at the steps near Bower Lane. While the entry/exit via Shelly Beach is never dangerous (with the exclusion of the slippery boat ramp), this score has to be interpreted as how "choppy" it gets in the bay, which is highly dependant on tide/headland protection (considered by the model) and whether the swell makes its way against the walkway wall. High water movement definitely brings low visibility.

• Bare Island: exposed to S-ESE for swell/wind wave and WNW-SW for wind chop. The score represents the water movement at the entrance/exit at the little ramp on the NW side of the island and on the East side (which is not used for entry but I thought useful to show conditions on this side). The effect of the tide (worsening the conditions as it gets higher) has been included, check the time indication on the on the dashboard and extrapolate to your dive time.

• Kurnell - The Monument: mostly exposed to refracted swell SSE-ENE, plus wind chop W-ENE. The score is for the entry/exit E of the whale monument and for the slightly more protected entry/exit W to the whale. Pick which one look more comfortable as they change quite a lot with the tide.

• Kurnell - The Steps & The Leap: the score indicates the water movement at The Steps for entry/exit and the slightly more exposed The Lead entry. Entries have the benefit of visibility of the swell hence can be timed, exits are usually more tricky so we set the model to reflect the conditions for exit.

• Chowder Bay: the score is almost completely dependant on wind chop from the opposite side of the harbour. While it never gets the power of a long oceanic wave, it does not take much to disturb the dive and stir particles up in the shallows around the nets.

• Camp Cove: like Chowder Bay, the score is almost exclusively dependent on wind chop. Both are safe harbours when oceanside conditions are prohibitive, and they get very busy on those days.

• Fairlight: susceptible to wind and swell coming from S-ESE. The score takes into account the challenge of crossing the shallow reef from/to the beach (which btw is almost impossible with low tide).

• Gordon's Bay: susceptible to S-ENE swell and wind wave, the score considers the water movement at the entry

• Shark Point: exposed and with challenges that we we described in the map page of this site. For the score, we considered the entrance from the slot in the reef platform and the exit via the pool. The exit that is sometimes indicated on the same platform of the entry is not recommended. Be aware of scuba diving restrictions as well as the extra 15 mins swim and navigation skills required to reach the pool. Tide has a relevant impact on the entry so we applied a strong score penalty when higher than 1 m.

• Freshwater: this is a tricky score because it reflects the water movement at the entry/exit from the W side of the rock pool and not at the point when the dive takes place and it's often affected by horizontal water movement due to the terraced nature of the point.

• Little Bay: exposed to NE-SSE swell and wind wave, but the entry/exit from the beach is facilitated. This is newly introduced site and scores need to be refined against condition reports.

• Oak Park: exposed to NNE-SSE, this is newly introduced site and scores need to be refined against condition reports. 

If interested in learning about the physics of the waves you can jump to that page here