St Lucia Geography & Climate

Saint Lucia is a volcanic island in the eastern Caribbean, about 43 kilometres long and 22 wide, lying between Martinique to the north and Saint Vincent to the south in the chain of the Lesser Antilles.

Volcanic origins

The island sits on the volcanic arc formed where the Atlantic plate slides beneath the Caribbean. Its interior is mountainous and forested, rising to 950 metres at Mount Gimie, and the slopes are steep enough that roads switchback constantly and a journey of twenty kilometres can take an hour.

The Pitons

Gros Piton and Petit Piton are volcanic plugs — the solidified cores of old vents, left standing after softer rock eroded away — rising from the sea to 771 and 743 metres respectively. With the geothermal field between them they form the UNESCO-listed Pitons Management Area, and the seabed drops steeply just offshore, which is why the diving is good.

The Sulphur Springs

At Soufrière, a collapsed caldera holds fumaroles, boiling pools and sulphurous mud. It is advertised as a drive-in volcano, which is accurate in that a road runs into the crater, and the last significant eruption was a steam explosion in the eighteenth century.

Two coasts

The Caribbean west coast is sheltered, with calm water, dark volcanic sand and the bays that hold the resorts. The Atlantic east is exposed to the trade winds, rough, and largely undeveloped. Marigot Bay, on the west, is a deep enclosed inlet that hid a British fleet from the French.

Rainforest and water

Rainforest covers much of the interior and is protected; the island is one of the wetter in the Lesser Antilles, and its rivers supply drinking water and the banana plantations that once carried the economy.

Saint Lucia has a tropical maritime climate moderated by the north-east trade winds, which blow almost constantly and make the heat far more bearable than the figures suggest.

Temperature

Between about 24 and 31°C all year, with very little seasonal variation — the difference between the coolest and warmest months is only a few degrees. Nights are mild, and the interior highlands are noticeably cooler and wetter than the coast.

The dry season

December to April is drier, less humid and sunnier, with the trades at their steadiest. This is the high season and the best weather, and the sea is calmest on the west coast.

The wet season

June to November brings higher humidity and more rain, though it typically falls as heavy afternoon showers lasting under an hour rather than sustained grey days. The island is at its greenest, the waterfalls run properly and prices fall.

Rain, by side of the island

Rainfall is very unevenly distributed. The windward east and the mountainous interior catch far more — over three metres a year on the highest slopes — while the leeward west coast around Vieux Fort gets well under half that. This is why the rainforest is inland and the resorts are on the west.

Hurricanes

The season runs from June to November with the peak risk from August to October. Saint Lucia is far enough south to be missed in many years, but Hurricane Tomas in 2010 caused severe landslides and flooding, and the steep terrain makes rainfall as dangerous as wind here.

Sargassum

Seaweed influxes affect the Atlantic east coast between roughly March and August in recent years. The Caribbean west coast, where most visitors stay, is largely unaffected.