The High Central Plateau: Mexico City, Puebla and San Miguel de Allende
October in Mexico City is the tail of the rainy season, and the rain arrives with almost comic punctuality: clear mornings, a heavy downpour between roughly 4pm and 7pm, then a cool evening. Daytime highs sit around 21-23C in Roma, Condesa and Coyoacan, dropping to about 10C after dark. Pack light layers you can shed at midday, a compact umbrella rather than a rain jacket, and closed shoes for wet cobblestones in the Centro Historico. A light scarf or jumper earns its place on the terraces of Condesa at night.
Around Puebla and San Miguel de Allende the same pattern holds, with colder nights in San Miguel given its 1,900-metre elevation and mornings that can sit near 8C. If your trip includes a day at Teotihuacan, add a hat and sunscreen; the site has almost no shade and the sun is strong even under cloud. I would keep one smart-casual outfit for Puebla's restaurant scene and skip the heavy coat, which you will carry for two weeks and wear once.
The Northern Border and Desert: Tijuana, Sonora and Chihuahua
Tijuana in October is mild and mostly dry, with daytime temperatures near 24C and evenings around 14C. The city is built on hills, so bring broken-in walking shoes if you plan to cross into downtown or wander Avenida Revolucion and the food stalls around Mercado Hidalgo. A windbreaker is more useful than an umbrella here, and a refillable bottle matters more than rain gear. The same advice scales up if you continue to Sonora or Chihuahua: strong sun, sharp temperature swings, and very little rain.
For desert country, pack long sleeves in a light fabric for sun cover and a fleece for mornings that start near 10C. If your plans include Copper Canyon, nights at the rim can approach freezing in late October, so a proper mid-layer is not optional. Skip cotton jeans for full-day walking; they stay damp and heavy. Hotels in Tijuana and Mexico City are filling for October weekends, so book a room with reliable air conditioning and heating rather than gambling on the weather.
The Gulf and Caribbean Coasts: Veracruz, Cancun and Tulum
October is still hurricane season on the Gulf and Caribbean, though the risk falls as the month goes on. Expect 30-32C days, high humidity and short, intense showers. Pack two swimsuits so one can dry, quick-dry shorts, sandals plus one pair of closed shoes for ruins, and a light rain shell that packs small. Reef-safe sunscreen is worth buying before you fly; it costs less at home than in a hotel shop. If you are heading to Tulum, add a torch for the unlit sections of the beach road.
Veracruz city is wetter and breezier than the Riviera Maya, with afternoon storms that clear quickly. Insect repellent is genuinely necessary inland from the coast, especially around Palenque and the cenotes. I would book a hotel with a pool and shaded outdoor space rather than one that promises a sea view, because October afternoons often send you indoors. Check the cancellation terms before you pay, and favour flexible rates over the cheapest non-refundable ones.
The Pacific and the South: Oaxaca, Puerto Escondido and San Cristobal
Oaxaca city in October is one of the best-value months of the year: warm days around 26C, cool nights near 12C, and the tail of the rains greening the hills around Monte Alban. Bring a hat, sunscreen and a jumper for evenings, plus shoes with grip for the polished stone streets near the Zocalo. The coast at Puerto Escondido and Mazunte stays hot and humid, so pack beachwear and a dry bag for boat trips; surf lessons and beach days dominate the itinerary.
San Cristobal de las Casas, at 2,200 metres, is genuinely cold at night in October, often below 10C, and its colonial streets are steep. A warm fleece and a rain jacket serve you better than an umbrella in the afternoon downpours. If you are combining highland and coast in one trip, pack a single soft bag you can compress; domestic flights and colectivos punish hard cases. I would book the highland stay first and build the beach days around it.