You'll be hard-pressed to find a blizzard or a tornado in Mexico. Unlike its neighbours to the north, Mexico gets few of the wild temperature swings that play out across the mid-latitudes. Hurricanes are not to be taken lightly in Mexico, however: they can cause major destruction along the east-facing coastlines of the Gulf of Mexico and the Caribbean as well as the south Pacific coast. Major flooding can occur along higher terrain when a dying hurricane moves inland, or even in less dramatic situations, such as persistent onshore flow against the south slopes of Chiapas, especially on deforested slopes. Apart from these occasional threats, Mexico's climate is mostly genial, although anyone expecting uninterrupted sunshine and constant warm air may be in for a surprise.
Plateau and Mountains
The main players in Mexican climate are the elevated landforms that cover more than half of the country and the bodies of water on either side. Many visitors, at some point, end up on the vast Central Plateau, which runs through the heart of Mexico. The plateau's elevation rises from an average of 1500m/4900ft on the north end – along the Rio Grande Valley – to about 2200m/7300ft on the south end Overall, the high altitude helps keep temperatures unusually mild for a region this close to the equator. Mexico City only rarely tops 30°C/86°F, and evenings are on the cool side throughout the year. The drought-prone northern end of the plateau is a bit warmer in summer and occasionally quite cold in winter. Periods of freezing weather aren't unusual, and a few snowflakes may fly by on gusty winds. Every spring, the plateau heats up quickly – May and June are the warmest months – before a monsoonal-like surge of moisture usually makes its way northward during the course of a few weeks. Following the surge, afternoons are slightly cooler but cloudier and more humid through the rest of the summer. Near-daily thunderstorms drop a healthy dose of afternoon rain, and a few steadier downpours occur at night. From central through south and east Mexico, mid-summer often brings a drier period of several weeks known as the canicula or veranitto, when nighttime rains may continue while afternoon showers become sparse. The rains taper off quickly in October, and winter actually provides more sun across the plateau than summer does. Across most of the plateau, January temperatures are dependably mild by day and chilly, but never frigid, at night.
The mountains ringing the plateau include the Sierra Mad re Occidental (west) and Oriental (east) and the Sierra Volcanica Transversal, a spectacular row of volcanoes just south of Mexico City. The Occidental and Transversal ranges have plenty of land in their cold terra fria zones (above 3000m/9900ft). A few substantial snows may fell – though most winter days are bright and sunny – and summer brings many brief spells of chilly dampness, with snow often clinging to the highest peaks. Winds are seldom very strong outside of thunderstorms. Conditions on the south side of the Transversal are considerably milder and moister than the north side; Cuernavaca, only a short drive over the Sierra from Mexico City, is known as the “city of everlasting spring”.
South and East
The lowlands ringing the Gulf of Mexico and Caribbean, including the Yucatan Peninsula, are hotter and more humid than the plateau in summer. Downpours are a little less frequent and reliable, but no less heavy, than on the plateau. Along the northeast coast, winter brings a few cool days and near-freezing nights. Once these howling nortes (northerlies) cross the Gulf of Mexico and reach the Yucatdn or Bay of Campeche coastlines, they usually deliver little more than clouds, wind, some drizzle and slightly cooler air, although heavier rains may fall on the highlands away from the coast. As on the Central Plateau, a pulse of heat arrives in spring before the summer rains begin. Hurricanes are a threat from June to November, with the latter half of the season somewhat more busy. They also prowl near the Pacific coast below the Sierra Madre del Sur from mid-May to November. Although a direct hit on the Pacific coast is always possible – over 200 died in the Acapulco area when Hurricane Pauline struck in October 1997 – the lion's share of these hurricanes stay just offshore, moving parallel to the coast from Puerto Angel to Manzanillo. As a hurricane draws near, coastal winds may turn offshore in a hot flow that squelches the sea breeze and toasts the usually humid beach resorts. It rarely rains along the south coast before June or after September, and the inland stretch from the Balsas Valley to Oaxaca can be parched and quite warm even in mid-winter. It's much wetter toward the Chiapas hills – an extension of Guatemala's forested mountains. Especially vigorous nortes may spill over the isthmus of Tehuantepec and howl into the Pacific.
The snakelike peninsula of Baja California produces sharp weather contrasts along Mexico's western fringe. The shallow, sheltered Gulf of California gets ridiculously warm – its water temperatures can reach 32°C/90°F in midsummer – while the cold current off the Pacific coast of Baja seldom exceeds 20°C/68°E This means you'll have vastly different seaside experiences on the humid gulf versus the California-like Pacific shore. Both areas are fairly cool and dry in winter, but in summer the gulf air is both scorching and moisture-laden, while the western Baja coast stays quite comfortable. The mid-summer rains are focused on the eastern gulf shore – from Mazatlan to Hermosillo – whereas the western Baja gets most of its scant rain in the winter. Once every few years a hurricane limps into the gulf, seldom causing major damage, except to fishing fleets. Cool waters make the west Baja coast almost hurricane-proof.