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Instructions on using Atlantic Ocean forecasts

Helgi Borg 28.2.2008

Keep the following points in mind:

  • Forecast maps for the Atlantic Ocean are automatic weather forecasts, made using a computer model.
  • View the shipping forecast in addition to the automatic, map-based forecast.
  • Bear in mind that short-term forecasts are more likely to be accurate than long-term forecasts.

Forecast map for the Atlantic Ocean

  • The black isobars signify the air pressure, in millibars, at the ocean surface (1 mb = 1 hPa).
  • The red, purple and blue isotherms show the temperature at 2 m above the ocean surface. A blue line denotes sub-freezing conditions; a purple line denotes 0°C and; a red line denotes temperatures above freezing.
  • Wind speed is displayed in metres per second (m/s).
  • The angle of the wind barb is indicative of the wind direction.
  • Wind-speed is symbolised by diagonal lines at the end of the barb; a long line represents 5 m/s, a short line 2.5 m/s and a triangle represents 25 m/s.

Vindörvar eru sýndar sem vindfjaðrir eða sem vindvigrar.

Temperature forecast:

  • Temperature levels are shown over the Atlantic Ocean in degrees Celsius (°C) at an altitude of about 1,500 m above the ocean surface. This altitude equates to an air pressure of 850 hPa.
  • The temperature at 1,500m altitude provides insight into the advection of warm or cold air.
  • The temperature scale on the image changes according to the temperature range of the forecast.

Precipitation forecast:

  • The map displays a forecast for the cumulative level of precipitation over a 6-hour period.
  • The colour scale denotes precipitation rates. The intensity ranges from 0.5 mm to 30 mm every six hours. Light and heavy precipitation is represented by light-green and purple shading, respectively.
  • Atmospheric pressure at the ocean surface is also shown in millibars (1 mb = 1 hPa).

The sliding bar below the map is used to change the validity time of the forecast

It is possible to change the validity time in many ways:

  • It is possible to click anywhere on the bar.
  • It is possible to click on the days above the bar to view the noon forecast for a specific day.
  • It is possible to click on the time below the bar.
  • It is possible to click on the arrows on either side of the bar to view the previous or the next validity time.


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