How To: Understand Sea Area Forecasts / Shipping News

I though I’d continue on from yesterday’s post and talk about how to interpret the radio sea weather forecasts.

In Ireland we get the Sea Area Forecast, also called the Marine Forecast on RTE Radio 1 (which comes from Met Eireann) twice a day. In the UK it’s more famously know as The Shipping News.

RTE 1 Marine Area Forecast is broadcast at 06:02, 12.53 & 23:55. In Ireland these are also broadcast more regularly on Marine VHF radio.

Radio Four Shipping News is broadcast at 00:48, 05:20, 12:01 & 17:54. (Useful for your next trip to Dover. All the pilots will listen to this).

Shipping New Forecasts use the Admiralty Sea Area regions (generally going clockwise). The Shipping News cover pretty much the entire Northern Europe Coastal waters.

So you need to see the map.

(See attached to this post also.)

For the English Channel the most relevant area is obviously Dover. For the South of Ireland the region is Fastnet with Shannon covering the South West and most of the West. Now you realise you can ignore most of the Shipping News stuff and just focus on the relevant area.

In Ireland however the Marine Forecast uses the Primary Headlands and off-shore Buoys (M1 to M6, usually only using M5 off the South-East) and is out to 30 Nautical miles form the coast. (See attached also.)

The Sea Area forecast always follows the same format.

It’s starts with a General Situation, describing the main weather systems affecting Ireland.
Also any Gale Warning in operation (Beaufort Force 8 or greater).
Small Craft Warning are issued if the wind is Beaufort Force 6 or greater.
Swell Warning is given with swell greater than 4 metres is expected.

The words that are used are not arbitrary but have specific meanings.

In time, Imminent means in the next 6 hours, Soon is between 6 and 12 hours, and Later is between 12 and 24 hours. The movement of the systems also have terms from Slowly (up to 15 knots) to Very Rapidly (greater than 45 knots).

Following the general situation, the Coastal Waters forecast is given, covering Wind, Weather and Visibility. Wind direction also includes some other words. Veering (a clockwise change), Backing (an anti-clockwise change).

Where the Forecast is similar, different areas are grouped together.

Wind is given using the Beaufort Scale I wrote about yesterday.
Weather uses a short list of self-explanatory words, Fine, Fair, Cloudy, Mist, Haze, Rain, Hail, Snow.
Fine means dry, mainly sunny and clear after dark. Fair means dry and sunny but may have some cloud.
Visibility in miles. Good means greater than 5 (nautical) miles, Moderate is 2 t0 5 miles, Poor is 1 kilometer to 2 miles. Less is Fog.
Pressure in hectopascals and the pressure tendency. For example “985 hPa, falling rapidly” means a low pressure dropping 3.5 t0 5.9 hPa per 3 hours, indicating bad weather coming quickly.

(For pressure 1000 hPa is the mean. Above is high, below is low, however the mean actually changes over the year, so a centre of 1005 hPa surrounded by centres of 1010 to 1020, is still a relative low pressure. This is a type of situation that can occur in the summer.)

So the forecast can be something like:

Forecast for coasts from Carlingford Lough to Roche’s Point to Erris Head and the Irish Sea –
Wind: North force 2 to 4.
Weather: Mist with patchy drizzle.
Visibility: Moderate to poor in mist but locally good.


3 thoughts on “How To: Understand Sea Area Forecasts / Shipping News

  1. Pingback: How To: Understand the Different Types of Open Water Swimming Locations Features and Hazards – I – The Ocean | LoneSwimmer

  2. Pingback: Studying weather online during a Force 10/11 blow | LoneSwimmer

  3. Pingback: Watching Dover and the English Channel | LoneSwimmer

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