their slower movement increases the duration of a particular wind direction. The variables of fetch and duration both influence how long wind acts over a wave as it travels since a wave reaching the end of a fetch behaves as if the wind died. During summer, heavy swells are generated when cyclones form in the tropics. Tropical cyclones form over warm seas, so their occurrence is influenced by El Niño & La Niña cycles. Their movements are unpredictable. Surf travel and some surf camps offer surfers access to remote, tropical locations, where tradewinds ensure offshore conditions. Since winter swells are generated by mid-latitude cyclones, their regularity coincides with the passage of these lows. Swells arrive in pulses, each lasting for a couple of days, with a few days between each swell. The availability of free model data from the NOAA has allowed the creation of several surf forecasting websites. Tube shape and speed Tube shape is defined by length to width ratio. A perfectly cylindrical vortex has a ratio of 1:1. Other forms include: Square: <1:1 Round: 1-2:1 Almond: >2:1 Peel or peeling off as a descriptive term for the quality of a break has been defined as "a fast, clean, evenly falling curl line, perfect for surfing, and usually found at pointbreaks." Tube speed is the rate of advance of the break along the length of the wave, and is the speed at which the surfer must move along the wave to keep up with the advance of the tube. Tube speed can be described using the peel angle and wave celerity. Peel angle is the angle between the wave front and the horizontal projection of the point of break over time, which in a regular break is most easily represented by the line of white water left after the break. A break that closes out, or breaks all at once along its length, leaves white water parallel to the wave front, and has a peel angle of 0°. This is unsurfable as it would require infinite speed to progress along the face fast enough to keep up with the break. A break which advances along the wave face more slowly will leave a line of new white water at an angle to the line of the wave face. Where: velocity of surfer along the wave face wave celerity (velocity in direction of propagation) peel angle In most cases