Oz Cyclone Chasers Cyclone Blog

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The OCC Weather Centre continues to evolve into one of the best weather analysis and forecasting tools available on the web. Over the past few days we have added some new maps and specifically, some new cyclone maps that will make forecasting tropical cyclones easier and allow all of our subscribers a chance to make more educated and informed cyclone forecasts. All of these features are ready now and we look forward to seeing them in action next week with all of the Tropical Cyclone development off Western Australia's coastline.   


Tropical cyclones are steered in the direction of winds through a deep layer of the atmosphere between about 1.5kms and 8kms high. Inside that deep layer, there are certain parts of the layer that play a more/less dominant role depending on the Tropical Cyclone's intensity. This has the effect of moving the Tropical Cyclone in different directions depending on how strong it is. OCC has been able to create charts that show which direction tropical cyclones are likely to be steered by depending on their intensity. Computer models are not good at picking up cyclone intensities, but they are very good at picking up steering forces that act on them. Our subscribers can now see the directional forces at work on tropical cyclones based on their intensities. Therefore if a tropical cyclone suddenly intensifies to a Cat 4 system for example, subscribers can quickly go into the steering forecast charts and see what changes this sudden increase in intensity is likely to have in the future track of a Tropical Cyclone.

Cyclone Steering forecast images are offered for the ACCESS R (very high resolution out to 3 days), ACCESS G (out to 10 days) and GFS (out to 16 days) computer models. 

Cyclone steering charts are produced for Tropical LOW/Cat 1, Cat 2/3 and Cat4/5 tropical cyclone systems. The Tropical LOW/Cat 1 charts can also be useful for severe and strong thunderstorm movement forecasting


Tropical Cyclones require sea surface temperatures of 26 degrees or more to be able to sustain their huge heat engines, and the hotter the ocean, the more potential energy their massive engines can transform into usable energy. OCC now has created sea surface temperature forecast charts to show the current and forecast ocean temperatures over the short to medium term. These charts will be an invaluable asset to assist in forecasting whether a tropical cyclone is about to pass over a warm pool of water or whether the system is about to approach a pocket of cooler water. Both of those have marked impacts on the developmental rates and potential of tropical cyclones. The charts also show us areas that are well below that 26-degree isotherm and therefore relatively safe from any major cyclonic impacts (although weakening systems may hit them, the chance of a strong cyclone in those areas will be minimal). Another very interesting thing models can do with sea surface temperatures is that they are now able to forecast of a slow-moving cyclone will actually change the sea surface temperature due to water upwelling, once again this can have a dramatic weakening effect on a system. 

OCC provides sea surface temperature analysis and forecast charts now for the ACCESS R (out to 3 days), ACCESS G (out to 10 days) and GFS (out to 16 days). 


Tropical Cyclone wind gusts at the surface can far exceed their sustained wind speeds. The new OCC wind gust charts can give us a clue as to what the maximum wind gusts are likely to be within the previous 3 hourly period (GFS, and ACC G) and in the previous one hourly period for the high resolution ACC R. A very useful tool when figuring out just how bad could conditions get and when that's expected to happen. 

Other Model Graphic Additions

  1. ‚Äč A Lifted Index chart with a surface wind chart - this shows us not only the potential instability of the atmosphere but also what the winds at the surface are doing, are they bringing in moisture? is there a boundary line or trough line underneath that instability to kick off storms? 
  2. A lifted Index chart with 950Hpa wind vectors - this shows us what the winds are doing just above the surface underneath the instability. This is useful to ascertain whether or not dry air exists just above the surface layer which can stop any clouds and storms growing 
  3. 1km storm relative helicity - this shows us how much turning is present in the lowest kilometre of the atmosphere - a very handy tool in tornado and waterspout forecasting.
  4. 3km storm relative helicity - this value shows us how much turning exists over a deeper layer of the atmosphere - a handy tool in forecasting rotating thunderstorms called supercells and forecasting stronger supercell induced tornadoes.