 Some rainbands move closer to the center , forming a secondary , or outer , eyewall within intense hurricanes . Spiral rainbands are such a basic structure to a tropical cyclone that in most tropical cyclone basins , use of the satellite @-@ based Dvorak technique is the primary method used to determine a tropical cyclone 's maximum sustained winds . Within this method , the extent of spiral banding and difference in temperature between the eye and eyewall is used to assign a maximum sustained wind and a central pressure . Central pressure values for their centers of low pressure derived from this technique are approximate . 
