GPSMAP 640 Owner’s ManualMarine Mode: Using XM WX Weather and AudioUnderstanding Water Temperature DataThe Water Temperature feature indicates the surface temperatureof the water, as indicated by the legend on the left of the screen.Temperature breaks are indicated by isotherm lines.Viewing Fish ForecastingTo view areas that contain optimal weather conditions for specificspecies of fish, from the Home screen touch Weather > Fishing> Menu > Fish Species. Touch a species of fish. Shaded areasindicate optimal fishing areas.Viewing Visibility InformationTo view visibility information, from the Home screen touchWeather > Visibility. Visibility is the forecasted maximumhorizontal distance that can be seen at the surface, as indicatedby the legend on the left of the screen. Contour lines show theforecasted change in surface visibility. To view the forecastedvisibility for another time period, touch Next Forecast. The screenshows the forecasted visibility for the next 12 hours. Continueto touch Next Forecast to view forecasts for the next 24 and 36hours.VisibilityViewing Buoy ReportsReport readings are taken from buoys and coastal observationstations. These readings are used to determine air temperature,dew point, water temperature, tide, wave height and period, winddirection and speed, visibility, and barometric pressure.Weather BuoyTo view a buoy report, touch a buoy ( ) on the Navigation chart,then touch Buoy.
