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On Tuesday December 6, 2016 at 11 a.m. EST (1500 UTC), a planned web system upgrade was performed. Due to this update we are experincing brief delays of data on the SSD web pages. We are aware of this problem and are working to correct it. For additional information see SATS message page.

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
     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: