Pacific Coast
Pacific Coast Geography & Climate
Geography
Mexico’s Pacific coast runs from Sinaloa down to the Guatemalan border, and for most of that distance the mountains reach the sea.
Sierra and shore
The Sierra Madre Occidental in the north and the Sierra Madre del Sur in the south leave only a narrow coastal plain, and in places none at all. The consequence is a coast of headlands and enclosed bays — Banderas Bay is among the largest and deepest in Mexico, dropping to over eight hundred metres close inshore, which is why whales come into it.
Lagoons and mangrove
Where the plain widens, rivers coming off the sierra have built coastal lagoons behind sandbars — Manialtepec, Chacahua, Agua Dulce — fringed with mangrove and important for birds. Several are bioluminescent, glowing when the water is disturbed at night.
The volcanic belt
Inland, the Trans-Mexican Volcanic Belt runs across the country behind this coast. The Colima volcano is one of the most active in North America, and Paricutin in Michoacan famously emerged in a farmer’s field in 1943 and grew four hundred metres in a year.
Earthquakes
The Cocos plate is subducting beneath the continent just offshore, which makes this one of the most seismically active coasts anywhere — the 1985 and 2017 earthquakes both originated here.
The bioluminescent lagoons
Several of the coastal lagoons — Manialtepec near Puerto Escondido is the best known — hold dinoflagellates that flash blue when the water is agitated. On a moonless night in the wet season, a hand trailed through the water leaves a glowing wake and fish streak away as lines of light. It is a seasonal and weather-dependent phenomenon rather than a guaranteed one, and it needs genuine darkness.
Surf
The offshore trench at Puerto Escondido lets deep-water swell arrive with almost no warning, producing the heavy beach break at Zicatela.
Climate Patterns
The Pacific coast is tropical throughout, and the year divides cleanly into a dry and a wet half.
The dry season
November to May brings almost no rain at all, with daytime temperatures of 28 to 32°C, low humidity and clear skies. The landscape turns brown and dusty by April, and this is the comfortable time to travel.
The wet season
June to October is hot and humid, with heavy rain concentrated into afternoon and evening storms. The coast greens dramatically, rivers run, and the lagoons fill; mornings are often clear, so a wet-season trip is workable if you plan around the afternoons.
Hurricanes
The eastern Pacific season runs mid-May to November, with the highest risk from August to October. This coast is genuinely exposed, and the warming ocean has produced storms that intensify with very little warning — Otis went from tropical storm to category five in about twelve hours before striking Acapulco in October 2023, killing dozens and wrecking the city. Warnings can be short; treat them seriously.
The sea
Warm year round, 26 to 30°C, and swimmable in every month. Surf is largest in the southern-swell season from May to September.
Planning around the afternoons
A wet-season trip here is more workable than the rainfall totals suggest, because the rain has a shape. Mornings are usually clear and often the best part of the day; cloud builds through the early afternoon and the storm arrives late, heavy and brief. Booking boat trips, dives and drives for the morning and treating the afternoon as indoor time makes June to October perfectly viable — and it is half the price.
Altitude relief
An hour inland and a thousand metres up, the sierra is ten degrees cooler and much wetter — cloud forest rather than dry coast.