The Dvorak Technique Explained

The Dvorak technique is a method using enhanced Infrared and/or visible satellite imagery to quantitatively estimate the intensity of a tropical system. Cloud patterns in satellite imagery normally show an indication of cyclogenesis before the storm reaches tropical storm intensity. Indications of continued development and/or weakening can also be found in the cloud features. Using these features, the pattern formed by the clouds of a tropical cyclone, expected systematic development, and a series of rules, an intensity analysis and forecast can be made. This information is then standardized into an intensity code.

Full Satellite Intensity Estimate Code:

EXAMPLE:     Ttt/cc/Lvv/xxhrs
     Where:
     T  - Tropical  (ST is used for Sub-Tropical systems)
     tt - Satellite Derived T-Number
     cc - System Current Intensity T-Number
     L  - Past Change  
          D - Developing
          W - Weakening
          S - Little or No change (Same)
     vv - Amount of Past change in T-Number
     xx - Hours over which the change was observed


EXAMPLE:     T3.5/3.5/D1.0/24hrs

Translation: The system appears on satellite imagery to be T-Number 3.5 storm. This value matches the Current intensity generating about 55 knots of sustained winds. The storm has developed a full T-Number in the past 24 hours increasing the wind speeds from 35 to 55 knots. The atmospheric pressure in the center of the storm has also lowered.

EXAMPLE:     T4.5/5.5/W1.0/24hrs

Translation: The system appears on satellite imagery to be T-Number 4.5 storm. The Current intensity is still 5.5 and the system is still generating sustained winds of about 100 knots. As a forecast tool, the Dvorak technique is showing a weakening trend and the likelihood of a lowering CI within the next 24hours.

Our coordination call information only contains the satellite Derived T-Number and the Current intensity (Ttt/cc).

Additional Information:

• Dvorak Current Intensity Chart
• Dvorak Tropical Cyclone Intensity Estimation Technique PDF