How did we pick the images for each cyclone type?
In Cyclone Center, one of your first tasks is to: “Pick the cyclone type, then choose the closest match.” You may be wondering how we found the images that you’re matching against.
One of the first steps in the Dvorak technique is to determine the storm’s “Pattern” strength. It’s an initial estimate of the storm’s strength based on how the clouds are organized. Here are Dvorak’s original patterns:
Each of these patterns gets stronger as we move from left to right, similar to in Cyclone Center. We could have used these patterns in Cyclone Center. However, the strengths are irregularly spaced, and there are only two levels of strength for Eye storms. We chose instead to use real satellite images to identify each pattern.
Some of the most highly trained Dvorak analysts in the world work in the Tropical Analysis and Forecast Branch (TAFB) at the National Hurricane Center. To take advantage of this expertise, we sorted the satellite imagery from the Atlantic in 2003–2006 by the strengths and cyclone types that they assigned. We then chose representatives from each category based on these criteria:
- Image quality
- Similarity to the original Dvorak patterns
- Representativeness of that image compared with others of the same strength and cyclone type
- Continuum of strengths for a given cyclone type
The last criteria was particularly important since we wanted to show a clear progression from weakest to strongest in each cyclone type. So if you are ever debating between two images to select, remember that they go from weakest to strongest and see if that helps.