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Great Circle Distance Calculator
Swell Arrival Calculator


Use this tool to calculate the Great Circle distance between any two points on the planet (in nautical miles) or to determine how long it will take a swell to travel to your beach. See instructions further down this page.


To use this tool just enter the:

  1. Coordinates of your beach (or any destination/buoy).
  2. The time the storm is first forecast (or actually started) to produce seas aimed at your location (Assumes "local time" unless you set your PC to GMT/UTC). (1)
  3. The coordinates of the center of the fetch area aimed at your destination from your favorite wave model (or a starting point).
  4. The maximum sea heights that were forecast or confirmed and that were aimed at your location. (1)
  5. Enter additional storm positions and sea heights (in 12 hour intervals). (1)
  6. Click on "Calculate Swell Arrival Time" or "Calculate Distance".
  7. The results display in a new window. Swell Arrival times are calculated for each swell period that should result (i.e. 17 sec period swells will start arriving at XXXX, followed by 14 sec period swells at XXXX, followed by 13 sec ....). Arrival time are calculated for each 12 hour interval, so results require some interpretation skill. Read the HELP section for more info.


(1) - These fields are not required when calculating Great Circle Distance only.

- Use the tab key to jump quickly between fields and the arrow keys to increment values in drop down boxes.
- Requires Internet Explorer 5.0 or Netscape 4.0 or higher.   If using Internet Explorer, Microsoft virtual machine (VM) must be installed for calendar/time functions to operate accurately.  (See HELP).

For more details: HELP

Distance formula written in 'C' by John Gair
Java applet written by Kumar Belday


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