The Dvorak Technique: An evolving Powerful Tool
for Cyclone Prediction.
Article by - AjithKumar (Chennai Weatherman)
"Typically, we hear terms such as formation, rapid intensification, weakening, eye wall replacement, etc. related to tropical cyclones. However, it's crucial to understand how current cyclone structures are analyzed and forecasted. That's why today, we'll delve into the evolution of the famous Dvorak Technique, which has been refined and improved with the advent of AI and remains one of the most relied upon tools in meteorology."
Cyclone prediction is a critical task that helps save lives and minimize damage from natural disasters. The Dvorak Technique is a tool used by meteorologists to determine the intensity of tropical cyclones, such as hurricanes and typhoons, based on satellite images.
The Dvorak Technique was developed by Vernon Dvorak in the 1970s and has since become an integral part of tropical cyclone analysis. It uses a set of objective rules to estimate the maximum sustained wind speed and the potential for further intensification of a tropical cyclone based on its cloud pattern.
The technique works by analyzing the central dense overcast and the eye of the storm, as well as the organization and curvature of the surrounding cloud bands. Meteorologists use these factors to assign a tropical cyclone intensity value on a scale of 1 to 7, with higher values indicating stronger storms.
The Dvorak Technique is a widely used method for estimating the intensity of tropical cyclones using satellite imagery. The technique uses several sources of information, including:
Cloud pattern: The arrangement, shape and size of cloud patterns in the storm system are analysed to estimate the intensity of the storm.
Central Dense Overcast (CDO) size: The size of the CDO, a mass of deep convective clouds around the storm's centre, is used to estimate the storm's intensity.
Cyclone CHENESO - Near Madagascar |
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Source: tropic.ssec.wise.edu
Convective banding: The organization and intensity of banding, or curved bands of thunderstorms, surrounding the storm's centre is used to estimate its strength.
Eye wall structure: The presence, shape, and size of an eye wall, a ring of deep convective clouds surrounding the eye of the storm, are analysed to estimate the storm's intensity.
Warm signature: The temperature difference between the storm's centre and surrounding cloud tops is analysed to estimate its intensity.
These sources of information are combined to produce an estimate of the tropical cyclone's intensity using the Dvorak Technique. The technique is subjective and based on the experience and skill of the forecaster.
One of the key advantages of the Dvorak Technique is its consistency and objective nature. It allows for a standardized method of analysis that can be applied globally, making it a valuable tool for tropical cyclone monitoring and forecasting.
The Dvorak Technique assigns a tropical cyclone intensity value on a scale of 1 to 7, known as the Tropical Cyclone (TC) number. The TC number is based on the satellite image analysis of the central dense overcast and the eye of the storm, as well as the organization and curvature of the surrounding cloud bands. The following is a detailed explanation of the different TC numbers:
TC Number 1: This value is assigned to a system that is not yet classified as a tropical cyclone but has the potential to develop into one. It is characterized by poorly organized convective activity with little or no evidence of a closed circulation.
TC Number 2: This value is assigned to a system that is still in the early stages of development, but with a closed circulation and some evidence of a central dense overcast. The system has the potential for further intensification, but wind speeds are typically below 34 knots.
TC Number 3: This value is assigned to a system with a well-defined central dense overcast and a well-defined eye, indicating that the system is in the early stages of intensification. The wind speeds are typically in the range of 34 to 63 knots.
TC Number 4: This value is assigned to a system with a well-defined central dense overcast and eye, and a symmetrical distribution of deep convection around the eye. The system is undergoing rapid intensification and wind speeds are typically in the range of 63 to 95 knots.
TC Number 5: This value is assigned to a system with a well-defined central dense overcast and eye, and a symmetrical distribution of deep convection around the eye. The system is in a mature stage of intensification and wind speeds are typically above 95 knots.
TC Number 6: This value is assigned to a system with a well-defined central dense overcast and eye, but with a decreased amount of deep convection surrounding the eye. The system is in a weakening stage, but wind speeds are still above 95 knots.
TC Number 7: This value is assigned to a system with a cloud-filled eye, little or no central dense overcast, and a poorly defined circulation. The system is in a weakening stage and wind speeds are typically below 34 knots.
It's important to note that the TC numbers are only one aspect of the overall tropical cyclone analysis and forecasting process. Meteorologists also use other tools and data, such as surface observations, reconnaissance aircraft, and numerical models, to determine the track and intensity of a tropical cyclone.
Image 1: TC Classification with Dvorak Technique 1975
Image 2: Automated Dvorak Analysis of Cyclone Vardah
Studies have shown the effectiveness of the Dvorak Technique in the North Indian Ocean basin, including in the Arabian Sea and Bay of Bengal. In a study published in the journal Natural Hazards, the Dvorak Technique was found to provide reliable intensity estimates for TCs in the North Indian Ocean basin and was shown to be a useful tool for TC forecasting.
In the North Indian Ocean basin, accurate and reliable intensity estimates are crucial for forecasting and warning purposes, as the impacts of TCs can be significant for coastal communities in the region. The use of the Dvorak Technique helps to provide more accurate and reliable information for these communities, enabling them to better prepare for and respond to TCs.
Moreover, the ongoing development and refinement of the Dvorak Technique, including the recent development of the AI-enhanced Advanced Dvorak Technique (AiDT), continue to improve the accuracy and reliability of TC intensity analysis and forecasting in the North Indian Ocean basin. This is helping to further our understanding of TCs in the region, and provides a basis for future research and improvements to the technique.
Overall, the use of the Dvorak Technique in the North Indian Ocean basin has proven to be an effective and valuable tool for TC intensity analysis and forecasting.
Prepared by - AjithKumar (Chennai Weatherman)