Llantrisant Sub-Aqua Club


Milford Haven Tide Tables & Weather
  Please note that the data contained in these tide tables does not account
for adverse weather conditions which may affect the tidal ranges.

They should not be used for navigational purposes.
Llantrisant SAC cannot accept responsibility for any errors in the data.

Click on the links below to access the tide tables by month

Dive Schedule March April May June
West Wales Diving July August September October


More tidal data for Milford Haven and other ports around the UK can be found on the website of the National Tidal and Sea Level Facility.

This is part of the The Proudman Oceanographic Laboratory (POL), which is a part of the Natural Environment Research Council. Where they carry out research on the following:

  • Wind-wave dynamics & sediment transport

  • Global sea level and geodetic oceanography

  • Estuary, coastal and shelf sea circulation & ecosystem dynamics

  • Marine technology & operational oceanography

To access this data click on the UK map (right).

Weather Information Sites
Map of Wales
United Kingdom

Local Time


Today's Weather Forecast
for West Wales

Atlantic Weather Chart

Useful Telephone Numbers & Links
Milford Haven Coastguard 01646 690909
Weathercall 0891 505314
Marine Call (weather) Wales 0891 505360
Marine Call (weather) Bristol Channel 0891 505359
Withybush Hospital (Haverfordwest) 01437 764545
Haverfordwest Police 01437 763355
South Pembrokeshire Police 01646 682121

Milford Haven Weather (Milford Weather.org.uk) Milford Haven Weather Map - Met Office
The Shipping Forecast - Met Office BBC - Coast & Sea
Milford Haven Port Authority Maritime & Coastguard Agency (MCA)
RNLI RNLI - Guidelines for SCUBA Divers
Outboard Engine Safety Check Propeller Information
Tidal Streams around Skomer Tidal Streams around Ramsay Island
UK Buoyage System Tides and Currents
South Wales Sea Fisheries - Byelaws South Wales Sea Fisheries - Guidance Leaflet

The Shipping Forecast...
issued by the Met Office, on behalf of the Maritime and Coastguard Agency.
Met Office Shipping Forecast BBC Shipping Forecast

Sea Areas around the UK (used in the shipping forecast)
Also showing some of the coastal weather stations

The coastal weather stations named in the Shipping Forecast
(some numbered on the map) are:
Tiree (Automatic) (1) Sandettie LV (Automatic) (6) Valley
Stornoway (2) Greenwich LV (Automatic) (7) Liverpool Crosby
Lerwick (3) St. Catherine's Point (Automatic) Valentia (11)
Wick (Automatic) Jersey (8) Ronaldsway (12)
Aberdeen Channel LV (Automatic) (9) Malin Head (13)
Leuchars (4) Scilly (Automatic) (10) Machrihanish Automatic
Boulmer Milford Haven
Bridlington (5) Aberporth
Note: LV = Light Vessel
Shipping Forecast Terminology
Gale warnings
Gale Force Winds of at least Beaufort force 8 (34-40 knots) or gusts reaching 43-51 knots
Severe gale Winds of force 9 (41-47 knots) or gusts reaching 52-60 knots
Storm Force of force 10 (48-55 knots) or gusts reaching 61-68 knots
Violent storm Winds of force 11 (56-63 knots) or gusts of 69 knots or more
Hurricane force Winds of force 12 (64 knots or more)
Imminent Expected within six hours of time of issue
Soon Expected within six to 12 hours of time of issue
Later Expected more than 12 hours from time of issue
Fog Visibility less than 1,000 metres
Poor Visibility between 1,000 metres and 2 nautical miles
Moderate Visibility between 2 and 5 nautical miles
Good More than 5 nautical miles
Movement of pressure systems
Slowly Moving at less than 15 knots
Steadily Moving at 15 to 25 knots
Rather quickly Moving at 25 to 35 knots
Rapidly Moving at 35 to 45 knots
Very rapidly Moving at more than 45 knots
Pressure tendency in station reports
Rising or falling slowly Pressure change of 0.1 to 1.5 hPa in the preceding three hours
Rising or falling Pressure change of 1.6 to 3.5 hPa in the preceding three hours
Rising or falling quickly Pressure change of 3.6 to 6.0 hPa in the preceding three hours
Rising or falling very rapidly Pressure change of more than 6.0 hPa in the preceding three hours
Now rising or falling Pressure has been falling (rising) or steady in the preceding three hours, but at the time of observation was definitely rising (falling)
(direction Indicates the direction from which the wind is blowing)
Becoming cyclonic Indicates that there will be considerable change in wind direction across the path of a depression within the forecast area
Veering The changing of the wind direction clockwise, e.g. SW to W
Backing The changing of the wind in the opposite direction to veering (anticlockwise), e.g. SE to NE

The Beaufort Wind Scale


Observations & wave size.



Flat calm - Sea like a mirror.


Light Air

Small ripples without crests. 0.1m


Light Breeze

Small wavelets. Crests do not break. 0.2m


Gentle Breeze

Large wavelets. Crests begin to break. 0.6m


Moderate Breeze

Breaking waves. Fairly frequent white horses. 1.0m


Fresh Breeze

Moderate waves. Many white horses and sea spray. 2.0m


Strong Breeze

Large waves. White crests and spray everywhere. 3.0m


Near Gale

Sea heaps up. White foam begins to be blown in streaks. 4.0m



Moderately high waves of greater length. Foam blown in well marked streaks. 5.5m


Strong Gale

High waves. Dense streaks of foam. Crests begin to roll over. Spray affects visibility. 7.0m



Very high waves with long overhanging crests. Dense white streaks of foam . Rolling sea becomes heavy. Visibility reduced. 9.0m


Violent Storm

Mountainous waves. Sea completely covered with foam. Visibility affected. 12.0m



Sea completely white with driving spray. Air filled with foam and spray. Visibilty seriosly reduced. 14m+

0 - 3
Suitable for diving anywhere around the coast.
4 - 5
Diving within the prescribed area only. (see Club Rules).
6 - 7
Sea too rough - if already out, return to shore.
8 - 9
Stay at home - don't even consider launching.
10 -12
Check your home insurance policy!

Note: The NOAA Small Craft Advisory regards sustained winds 25 knots or greater and seas 10 feet (3m) or greater to be hazardous to small craft. This equates to Beaufort Force 6. As a club we do not operate in conditions equal to Force 5 or above.

Weather and diving.

The Highs and Lows of UK Weather

The UK's mid latitude position between 50 - 60°N leaves it between the warm south and the cold north. The atmosphere is driven by a need to reduce this temperature gradient by sending warm air north and cold air south using cyclones and anticyclones, or the highs and lows which make up our 'synoptic-scale' weather, and which we see on the pressure charts.

When low pressure systems form in the western Atlantic, they pick up warm moist air which is then mixed with cooler air from the north as they move east across the top of the Azores high. The boundaries between these air masses are marked by fronts.

A typical anticlockwise rotating low centre will reach western Ireland and then curve north up the western Scottish coast. The warm front moves across the UK first, with warm moist air behind it bringing spells of rain and often reduced visibility with south to south westerly winds. The cold front chasing along behind is the boundary between this warm moist air, and the cooler more unstable brighter and more showery weather behind, with winds typically from the south west to north west.

The transition of these fronts is something the diver has to take note of as the passage of these fronts over head will bring strong winds and occasionally heavy rain which can quickly turn a pleasant day's diving into a dash for shore.

High pressure usually follows these low pressure systems. These anticyclones are clockwise rotating sinking air masses which we associate in the summer season with light winds and sunny skies, and often building afternoon onshore or sea breezes.

The pressure imbalance created between the high and low pressure areas is what drives the wind as it tries to reduce this pressure gradient. Wind which we see on the water is, in the northern hemisphere, more backed (further left looking upwind) than this 500m pressure gradient wind due to the effect of friction or drag on the wind by the surface.

The rougher the surface the more drag on the wind, i.e. winds are more backed over the land (20 - 40°) than they are over the smoother sea (10 - 20°). This is something to look for on the water when winds are blowing off the shore, as they will veer (clockwise, or shift right looking upwind) downwind of the shore.

Heat from the sun has a noticeable effect of the surface winds. How many mornings have you looked out the window to see calm conditions but by lunchtime the winds have picked up nicely?

During the night the earth cools and so in turn it cools the air directly above it, which reduces its 'energy' or mixing and so reduces the wind speed.

As the sun heats the earth, the air next to the surface begins to warm and so begins to rise and mix as cooler air sinks to the surface to replace it, which results in an increased wind speed.

Friction and heating are just two examples of the many factors which we must take into account when on the water. The forecasts we receive are often for a much wider area and there are small scale processes which affect the local winds.


Miles or Nautical Miles?

The nautical mile is based on the circumference of the earth at the equator.

Since the earth is 360 degrees of longitude around, and degrees are broken into 60 "minutes", that means there are 360 * 60 = 21,600 "minutes" of longitude around the earth.

This was taken as the basis for the nautical mile; thus, by definition:-
1 minute of longitude at the equator is equal to 1 nautical mile.

For geometrical reasons, we use the minute of latitude on charts to correspond to a nautical mile rather than the minute of longitude. Minutes of longitude shrink as they move away from the equator and towards the poles; minutes of latitude do not shrink.

So the earth is ideally, by definition, 21,600 nautical miles (and 21,600 "minutes" of longitude) in circumference at the equator. (By the way, the nautical mile is about 1.15 larger than the "statute" mile used by land lubbers).

To convert Miles to Nautical Miles - Multiply by 0.86
To convert Nautical Miles to Miles - Multiply by 1.15

Example: Our boat insurance policy allows us to operate 20 (land) miles from shore.
Therefore in nautical terms we can operate 20 * 0.86 = 17.2 nautical miles from shore.

The Jet Stream

The jet stream is a strong flowing ribbon of air that flows around our planet high up in the atmosphere, at around the level of the tropopause.

Situated between the troposphere and the stratosphere, the Jet Stream is approximately 11 kilometres above the surface of the Earth at the poles and around 17 kilometres above the surface of the Earth at the equator.

The jet stream flows at around 160kmph (100mph).

We often hear that the jet stream is responsible for influencing the weather in the UK, so it is natural to wonder what causes the jet stream and why it has such an influence on the weather we experience on the ground.

Click on the map above to see the Jet Stream

Jet streams form and are strongest where variable air temperature gradients are steepest. This is normally seen in two zones:

  • The boundary between the polar and mid latitude air: The Polar Jet

  • The boundary between the mid latitude air and tropical air: The Subtropical Jet.

Summary of the Jet Stream and the weather it creates:

  • The position of the jet stream over the UK determines the type of weather we experience.

  • If the polar front jet is situated significantly to the south of the UK we will experience colder than average weather.

  • If the polar front jet is situated to the north of the UK we will experience warmer than average weather.

  • If the polar front jet is situated over the UK we will experience wetter and windier than average weather.

  • If the polar front jet has a large amplification then cold air will travel further south than average and warm air will travel further north than average.

  • The direction and angle of the jet stream arriving at the UK will determine what source of air (i.e. cold, dry, warm, wet, from maritime or continental sources) the UK experiences.

Global Weather Data
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SAA Club 349
Eagle GPS
Atlantic Pressure Charts
UK Wind Chart
UK Wind Map
UK Tidal Predictions
Tidal Prediction
Admiralty Charts
Imray Charts
West Wales Sailing
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