Coastal Cloud Photographs

Within 10 minutes of this photo being taken the flag in the foreground was blowing just as hard in the opposite direction. I am sure the rapid development of the storm was due to a northerly sea breeze moving up the river at the same time as a westerly sea breeze moved in from west of Trevose head. This led to a sort of 3 way convergence with the southerly gradient wind. This is what happened at Boscastle storm in 2004, and is typical of many north coast events.

The Sea-Breeze Effect

Down in Penzance, at the tip of Cornwall, the surrounding sea clearly has a marked influence on the weather.

In particular, due to the sea breeze effect, the coasts are much sunnier than inland . When the air is rather unstable the effect can be dramatic. Cloudless on the beaches, billowing cumulus just a mile inland.

The first 2 photos show the effect.

The top photo is taken from Porthleven, looking south towards the Lizard point. In this case the gradient wind was north, blowing the cloud along the spine of the Lizard, and off the southern point. The second photo is looking inland from Coverack.

Coastal Fog

What appears to be sea fog is often coastal fog. A mile or 2 out to sea it can be sunny, the fog forms as the air starts to rise up the cliff, and quickly dissipates as it moves inland.

This photograph was taken during a moist WNW airstream after 2 months dry weather. Hence the totally brown fields. (The brown fields are grass, the golden fields corn, and the greenish fields mainly broccoli).

The mist in the centre of the photo is above Sennen Cove (1 mile NNE of Land’s End). The mist along the horizon is along the north coast, from Cape Cornwall to Pendeen.

As the peninsula in west Cornwall is so narrow, the sea-breezes from the north & south coasts commonly converge in the middle.

In most cases this gives a distinct line of cumulus / strato-cumulus as in this photo, which was taken just north of Penzance looking NE towards Camborne.

At other times this convergence can give rise to heavy showers or thunderstorms as seen in the next photo taken from Penzance Harbour looking ENE. Over the sea it was virtually cloudless.

At St. Ives on the north coast it was also sunny. The showers ran ENE up the peninsula, along the convergence zone, for several hours.

The north coast of Cornwall is particularly prone to severe thunderstorms as the sea breeze sets in. On 29th June 2005 there was an exceptionally severe storm over St. Merryn (just west of Padstow). Many properties in St Merryn, and villages just to the south, were flooded.

The morning had been very warm with sunny periods and a light southerly gradient wind. When the sea breeze set in the speed the storm developed was amazing. I had lunch in Rock, which faces west across the Camel estuary towards Padstow and I had a grandstand view of events. This photo was taken looking west towards Padstow at 12:52 BST. The darkest area marks the sea-breeze limit (sea to the right).

Sometimes no sea breeze develops, often because the gradient wind is strong enough to mask the effect. In these conditions cumulus still develop much more readily over the land during the day, but are not in any well defined line. During the night / early morning the situation is reversed with most of showers being over the sea and the immediate coast.

Sea Breeze and Sea Fog

Sometimes the sea breeze will bring in sea fog. In this photo the fog is drifting into Mount’s Bay, and around St. Michael’s Mount.

When the sea breeze is coming in against an off-shore wind it struggles to reach the coast. The picture below was taken at Sennen Cove, looking north towards Cape Cornwall.

The sea breeze didn't quite make the beach, but it brought sea fog in to within
a few hundred metres at one point.

The fog at the top of the cliff was drifting back westwards under the gradient wind, whilst at sea level it was moving towards the beach. You could work out exactly where the gradient wind / sea breeze convergence zone was. Open Atlantic to the left, beach to the right.