Map from Google - Mexico

Mexico is a vast country and has different types of climate, however, it is generally arid on the west coast and the inland central-northern highlands, it becomes moderately rainy in the mountain ranges and the southern plateaus, while it's very rainy in some tropical southern areas. Summer is the rainiest season almost everywhere.
The temperature increases gradually from north to south, so that the south has a purely tropical climate. Altitude plays an important role as well: there are many cities located at high altitude, including the capital, which have a cooler climate.
During winter, a cold wind from the United States, the "Norte" can blow, able to lower the temperature abruptly, especially in the centre-north. Because of this wind, the northern inland areas (and a little less the northern coastal areas) during winter may experience cold waves, especially in hilly and mountainous areas.

1- The mild coast

Baja California, coast
In the peninsula of Baja California, nearly a continuation of California, the climate is very mild on the west coast, where daytime temperatures go from 19/20 degrees Celsius (66/68 °F) in winter, to 24/25 °C (75/77 °F) in summer in the northern part. The sun shines throughout the year, and the rains, poor, fall from November to March; total rainfall is around 200/250 millimetres (7.8/10 inches) per year. Here, as in California, a cold current flows, which makes the sea cool and causes some fog, but in return it provides sun, little rain and a pleasant climate. However, the temperatures can suddenly increase, surpassing even 40 °C (104 °F), when the wind blows from the interior. A city that is located in this area is Tijuana, just south of the border with the United States, a short distance from the greater San Diego area.
Here are the mean temperatures of Rosarito, in the coast near Tijuana (in summer the centre of the city is slightly warmer, because of its distance from the coast).
Average temperatures - Rosarito
Min (°C)101010111314161716151210
Max (°C)191919202122232524232120
Min (°F)505050525557616361595450
Max (°F)666666687072737775737068

The rainfall is scarce and amounts to 260 mm (10.2 in) per year, and follows the Mediterranean pattern, being concentrated in autumn and winter. Here is the average precipitation.
Average precipitation - Rosarito
Prec. (mm)5052571781026102730260

The temperature of the sea in this part of the coast is very cool even in summer, as we can see in the following table.
Sea temperature - Rosarito
Sea (°C)151515151617192020191816
Sea (°F)595959596163666868666461

Moving towards the south, the sea becomes progressively warmer. In the southern part of Baja California, the sea temperature reaches 21/22 °C (70/72 °F) from August to October, while in Baja California Sur, the sea becomes decidedly warmer.
East of the coast, in mountain ranges of Sierra Juárez and San Pedro Mártir, the winter temperature decreases due to the altitude, with frequent night frosts, while summer gets hot, because the distance from the sea (which is cooled down by the cold current) is even more important than altitude, although above 1,000 metres (3,300 feet), the nights get cool.

2- Sonoran desert

Climate of the Sonoran Desert
The Sonoran Desert, the westernmost of the Mexican deserts, is characterized by an increase in rainfall in the latter part of the summer, a kind of "little monsoon" from July to mid-October, which may bring some thunderstorms and an increase in humidity. The central-southern part of Baja California (administratively divided in the states of Baja California and Baja California Sur) can be included in this area, although the climate along the west coast is milder than that of east coast overlooking the Gulf of California and of the interior.
In fact, continuing south on the aforementioned west coast, the temperature rises gradually, to the point that highs in Baja California Sur reach 20/22 °C (68/72 °F) in winter and 30 °C (86 °F) in summer in the northern part, and 25 °C (77 °F) in winter and 32 °C (90 °F) in summer in the far south.
In the eastern side, the coast of the Gulf of California in summer is much warmer than the western coast, because the cold current doesn't arrive here, and being a closed gulf, in summer it heats up a lot. Here, the daytime summer temperatures are around 35/36 °C (95/97 °F), while in winter they are around 20 °C (68 °F) in the north, 22 °C (72 °F) in the centre, and 25 °C (77 °F) in the south.
Baja California is a barren, almost desert peninsula: along the coasts, annual precipitation is around 100/150 mm (4/6 in). But in the hills of Baja California Sur, the little monsoon brings additional rainfall, so that total rainfall exceeds 400 mm (16 in) per year. This area, known as Sierra de la Laguna, is covered by woods (and therefore should be excluded from the desert area, as indicated by the small circle in the map).
As part of the little monsoon, especially in August and September, Baja California Sur (more rarely Baja California) can be affected by low pressure areas and tropical cyclones that form in the Pacific Ocean off the southern coast of Mexico. These disturbances, usually less intense than those that form in the Gulf of Mexico, can also penetrate in the continent, affecting the northern part of Sinaloa and the state of Sonora.
Cabo San Lucas is located at the southern tip of Baja California. Here, as in the rest of the peninsula, the climate is arid; winter is sunny, with cool nights, around 12/13 °C (54/55 °F), and pleasantly warm days, around 26/27 °C (79/81 °F). Spring is warm and sunny: daytime temperatures reach 29 °C (84 °F) already in April. Summer is hot, with highs around 32/34 °C (90/93 °F), but in the second part, from mid-July to October, there's some chance of showers and thunderstorms, sometimes intense, especially in September, due to the little monsoon.
Average temperatures - Los Cabos
Los CabosJanFebMarAprMayJunJulAugSepOctNovDec
Min (°C)131313151719232423211714
Max (°C)252627293032333433322926
Min (°F)555555596366737573706357
Max (°F)777981848690919391908479

In this southern part of Baja California, the rainfall pattern is opposite to that of the northern part, because as we said the rains are concentrated in late summer. Here is the average precipitation.
Average precipitation - Los Cabos
Los CabosJanFebMarAprMayJunJulAugSepOctNovDecYear
Prec. (mm)1220100156085352020245

Here the sea is very warm in summer, while in winter it is a bit cool, but not impossible for swimming.
Sea temperature - Los Cabos
Los CabosJanFebMarAprMayJunJulAugSepOctNovDec
Sea (°C)222121222325272929292624
Sea (°F)727070727377818484847975

In the north-east of the state of Baja California, we find the Yuma Desert, where the town of Mexicali is located: it is an area of developed lands and recent settlements, where summer temperatures reach extremely high values: even more than 55 °C (131 °F)! This is the hottest place in Mexico, as well as one of the hottest places in the world.
Average temperatures - Mexicali
Min (°C)681013172126262216106
Max (°C)202326303540424138322520
Min (°F)434650556370797972615043
Max (°F)6873798695104108106100907768

Rainfall is very low, below 100 mm (4 in) per year, and the increase between mid-summer and autumn, here is also very low. Here is the average precipitation.
Average precipitation - Mexicali
Prec. (mm)118821051210941384

Southeast of this desert, we find the Altar Desert, a sand desert whose appearance resembles the vast areas covered with dunes of the Sahara.

Sonoran Desert

The western area of the state of Sonora is part of the Sonoran Desert itself, and as we have seen with regard to Baja California Sur, it experiences an increase in precipitation from July to October. From July to October, the wet winds lower a bit the temperature, to the point that the hottest month is often June, but they also raise relative humidity. In this area we find the important city of Hermosillo, which has a dry winter, pleasantly warm during the day (even though nights can be cold), and a very hot summer, with average highs around 40 °C (104 °F) in June.
Average temperatures - Hermosillo
Min (°C)91112151924262524191310
Max (°C)242628323540393837342824
Min (°F)485254596675797775665550
Max (°F)757982909510410210099938275

From July to October, the little monsoon brings some rains and thunderstorms, sometimes strong, which, however, do not last long, so that soon the sun will shine again. The rainiest month is August, with almost 100 mm (4 in) of rain. Relative humidity increases as well, rising from 33% in June, to 55% in July and 51% in August and September, so that the heat becomes sweltering. Here is the average precipitation.
Average precipitation - Hermosillo
Prec. (mm)2020105579010055201530365

3- Chihuahuan Desert

The mountain range called Sierra Madre Occidental, which separates the states of Sonora and Chihuahua, and continues south to the states of Sinaloa, Durango and Nayarit, experiences a period of monsoon rains quite long (mid-June to early October), and intense, so that precipitation exceeds 400 mm (16 in) per year (July is usually the rainiest month), so the climate of these mountains is semi-arid rather than desert. Above 1,000 metres (3,300 feet), rainfall even exceeds 700/800 mm (27/31 in), so that the landscape becomes green. In the southern part of the Sierra Madre Occidental, even winter becomes quite rainy, in fact rainfall exceeds 1,000 mm (40 in) per year.

To the east of the Sierra Madre Occidental and to the west of the Sierra Madre Oriental, ie between the two ranges, we find the Chihuahuan Desert, an area of highlands, located in the states of Chihuahua and Coahuila and the north-east of Durango, where the climate is characterized by a wide daily temperature range, by sunny and dry winters, with possible night frosts, and hot summers, which become moist from mid-June to mid-October, when the sun frequently shines, but it alternates with rains and thunderstorms. Because of the altitude, the summer heat is less intense than in the lower areas of the Sonoran Desert, however, sometimes the temperature can reach or exceed 40 °C (104 °F).
An important city of this region is Ciudad Juarez, located in the far north, at 1,100 metres (3,600 feet) above sea level, on the border with Texas; here the average in January is 8 °C (46.5 °F), that of July is 29 °C (84 °F).
Average temperatures - Ciudad Juarez
Ciudad JuarezJanFebMarAprMayJunJulAugSepOctNovDec
Min (°C)1261014202220171141
Max (°C)151822263136363431262016
Min (°F)343643505768726863523934
Max (°F)596472798897979388796861

Average annual precipitation is 265 mm (10.5 in), and September is the rainiest month. Here is the average precipitation.
Average precipitation - Ciudad Juarez
Ciudad JuarezJanFebMarAprMayJunJulAugSepOctNovDecYear
Prec. (mm)171347101345476426813268

Other cities are Chihuahua, 1,400 metres (4,600 feet) above sea level, where the average is 9.25 °C (48.7 °F) in January, the hottest month is June with an average of 26 °C (79 °F), 450 mm (17.5 in) of rain per year fall, and August is the rainiest month; Torreon, 1,100 metres (3,600 feet) above sea level, with a January average of 14.5 °C (58 °F), a June average of 28 °C (82 °F), 230 mm (9 in) of rain per year, and September as the rainiest month; Saltillo, 1,700 metres (5,600 ft), January average of 12 °C (53.5 °F), June average of 23 °C (73 °F), 370 mm (14.5 in) of rain per year, and September as the rainiest month. During winter, cold spells can be intense especially in the north: in Ciudad Juarez the temperature can drop below -15 °C (5 °F).
Average temperatures - Torreon
Min (°C)791216192121201915107
Max (°C)222526333535343432302623
Min (°F)454854616670706866595045
Max (°F)727779919595939390867973

4 - Eastern plains

Eastern plains
In this eastern area, overlooking the Gulf of Mexico (including the state of Tamaulipas, the east of Nuevo Leon, the south-east of San Luis Potosi, the north-east of Hidalgo, and the north of Puebla and Veracruz), along the coast, and in plains and hills below 500 metres (1,600 feet) of altitude, winter is very mild, sometimes pleasantly warm, but we can not exclude some brief cold spells, while summer is hot and humid. Annual rainfall generally ranges from 500 to 1,000 mm (20 to 40 in), and increases gradually from north to south and near the highlands, where it even exceeds 1,000 mm (40 in) per year. The rainy season runs from May to October. In this area we find the city of Monterrey, 500 metres (1,600 feet) above sea level, where the average temperature of January is 14.5 °C (58 °F), that of July is 29 °C (84 °F), and rainfall amounts to 590 mm (23 in) per year, including more than 50 mm (2 in) per month from May to October, with September as the rainiest month.
Another city is Tampico, on the coast, which has an average of January of 19 °C (66 °F), and of August of 28.5 °C (83.5 °F).
Average temperatures - Tampico
Min (°C)151619212425252524221916
Max (°C)232427293132323231302724
Min (°F)596166707577777775726661
Max (°F)737581848890909088868175

Tampico receives 1,150 mm (45 in) of rain per year, including more than 100 mm (4 in) per month from June to October. Here is the average precipitation.
Average precipitation - Tampico
Prec. (mm)302015255019515017026513540551150

At Tampico, the Gulf of Mexico is warm enough for swimming all year round, although in winter it drops to 23 °C (73 °F).
Sea temperature - Tampico
Sea (°C)232323252728292929282624
Sea (°F)737373778182848484827975

Let us now talk about central and southern Mexico, where the difference between winter and summer decreases, due to low latitude, and the temperature varies mainly with altitude, so that we can distinguish among the tierras calientes, from the plain to 1,000 metres (3,300 feet), the tierras templadas, between 1,000 and 2,000 metres (3,300 and 6,600 feet), and the tierras frìas, above 2,000 metres (6,600 feet).

5 - Tierras frías

In the plateau there is a considerable difference in temperature between day and night, especially in the dry season, and sun's rays are very strong, even though the temperature is not so high. As for the rains, there is a dry season from November to April, and a rainy season from May to October.

Tierras frìas
The huge capital, Mexico City is located in the southern part of the plateau, at an altitude of 2,200 metres (7,200 ft); administratively it belongs to the Federal District. Winter is dry and sunny, with cold nights: in January and February lows are around 6/7 °C (43/45 °F), but sometimes they can drop a few degrees below freezing (0 °C or 32 °F), while days are pleasant, so that highs are around 21/23 °C (70/73 °F). In spring the temperature rises gradually until April and May, which are the months with the highest daytime temperatures, around 27 °C (81 °F), while night-time temperatures are still pretty cool, around 11/12 °C (52/54 °F). In June, the daytime temperature stops increasing, in fact it drops by a few degrees, to around 23/24 °C (73/75 °F), because of the summer monsoon, which brings clouds and rains from June to September. In a typical year, 710 millimetres (28 inches) of rain fall, with a maximum of 160 mm (6.3 in) in July.
The Mexican capital is polluted, and is wrapped in an almost constant mist.
Read more: the climate of Mexico City.
Average temperatures - Mexico City
Mexico CityJanFebMarAprMayJunJulAugSepOctNovDec
Min (°C)6791112121212121087
Max (°C)212326272725232322222221
Min (°F)434548525454545454504645
Max (°F)707379818177737372727270

6 - Tierras templadas

Climate of the Tierras Templadas

In the lands of south-central Mexico that are located at intermediate altitudes, the average temperatures are mild, although sometimes it can get cold on winter nights, while sometimes during the day it can get hot. In this area, we can mention a city like Guadalajara, at 1,500 metres (5,000 feet) above sea level, in the state of Jalisco, whose average temperature is 17.5 °C (63.5 °F) in January, and 25 °C (77 °F) in May. Here are the average temperatures.
Average temperatures - Guadalajara
Min (°C)101113151718171717151311
Max (°C)252729313231272727272725
Min (°F)505255596364636363595552
Max (°F)778184889088818181818177

Rainfall amounts to 970 mm (38 in) per year, with a long dry period, and a rainy season from June to early October. Here is the average precipitation.
Average precipitation - Guadalajara
Prec. (mm)205472018527522016550158972

In the southern highlands, the temperatures are slightly higher and rainfall is more abundant, as happens in the Chiapas highlands, where in addition even October and November are rainy.

7 - Tierras calientes

Climate of the Tierras Calientes

In the plains and hills of the south, the climate is hot all year round, with a dry season (December to April or November to May, depending on area), and a rainy season (May to November or June to October). The warmest period is the one that precedes the rainy season, usually the months of April and May. But then with the arrival of the rains, the humidity increases, and so does the feeling of sultriness. Usually the rains come in the form of thunderstorms, sometimes strong, in the afternoon. In addition, the rains tend to become more abundant as you move south. In the interior of the southern states, precipitation exceeds 2,000 mm (80 in) per year, but in some cases it exceeds even 3,000 mm (120 in). The south of the state of Veracruz, the south-east of Oaxaca, the state of Tabasco and northern Chiapas (see Palenque, Yaxchilan) are very rainy areas: here there are moderate rains also in winter, and therefore there is not a real dry season.
In Acapulco, along the coast of the state of Guerrero, the climate is hot all year round, but the dry season, from November to May, is sunny and it almost never rains. The sea is always warm, not going below 28 °C (82 °F) in winter.
Average temperatures - Acapulco
Min (°C)232424242525252525252524
Max (°C)303030313232323232323231
Min (°F)737575757777777777777775
Max (°F)868686889090909090909088

The mountains located north of the city protect this coast from cold winds (while this does not happen in the coast on the Gulf of Mexico, see below). However, in the rainy season, from June to October, the rains are abundant and sometimes torrential. Here is the average precipitation.
Average precipitation - Acapulco
Prec. (mm)133142526024528030013017121284

Here, and in general along the southern coast of Mexico, during the rainy season tropical cyclones, called cordonazos, can form, which are able to cause gale force winds and heavy rains. Traditionally, El cordonazo de San Francisco is a storm that occurs on October 4, the day of St. Francis.

Further north, in Puerto Vallarta, in the state of Jalisco, the climate is similar to that of Acapulco, but during winter nights are cooler, and they can occasionally get pretty cool, around 10 °C (50 °F), and this can still happen, though more rarely, in March and April.
Average temperatures - Puerto Vallarta
Puerto VallartaJanFebMarAprMayJunJulAugSepOctNovDec
Min (°C)171617172023232323222018
Max (°C)292929303132333434343230
Min (°F)636163636873737373726864
Max (°F)848484868890919393939086

The sea in Puerto Vallarta is warm enough for swimming even in winter, since it doesn't go below 24 °C (75 °F).
Sea temperature - Puerto Vallarta
Puerto VallartaJanFebMarAprMayJunJulAugSepOctNovDec
Sea (°C)252424242628293029292826
Sea (°F)777575757982848684848279

In the east, in the Yucatán Peninsula (states of Campeche, Yucatán and Quintana Roo), the climate is generally warm or hot all year round, but winter is not as dry and sunny as in the south coast: the months of December and January, when highs are around 28/30 °C (82/86 °F), are quite rainy; besides in winter, from December to March sometimes the cold wind from the United States, the Norte, can blow, so that the minimum temperature can drop to 10 °C (50 °F), and even below. In Cancun, the least rainy period runs from February to April, and the driest month is April, so it is an advisable destination for Easter holidays, when the Norte is less likely to blow.
Average temperatures - Cancun
Min (°C)212122232425252525242321
Max (°C)282930323333333433313028
Min (°F)707072737577777777757370
Max (°F)828486909191919391888682

The Gulf of Mexico in Cancun and the Riviera Maya is warm enough for swimming all year round.
Sea temperature - Cancun
Sea (°C)262626272828292929292827
Sea (°F)797979818282848484848281

The rainy season runs from May to November, although the rains are abundant especially in June, and between September and mid-November; this is a hot and sultry period, during which there's no shortage of sunshine, because the rains generally occur in the form of downpour or thunderstorm, so they don't last long. Similar situation is found in Isla Mujeres and the Mayan Riviera south of Cancun (Playa del Carmen, Tulum, Cozumel, etc..): here March and April are the driest and sunniest months, and April is the best month.
During the rainy season, Yucatán and the coastal area bordering the Gulf of Mexico may be affected by hurricanes, especially in the period from August to October, however the hurricane season runs from June to November. Hurricanes come from the south or east, and sometimes can be destructive.

8 - Mountains

In high mountains and volcanoes of south-central Mexico, the climate is cold, although given the low latitude, this happens at very high altitudes. For example, in the volcano Nevado de Toluca, southwest of Mexico City, at 4,300 metres (14,100 ft) above sea level, the average temperature in January is 2 °C (35.5 °F), while that of April and May, the warmest months, is 5 °C (41 °F).
Average temperatures - Nev. de Toluca
Nev. de TolucaJanFebMarAprMayJunJulAugSepOctNovDec
Min (°C)-3-2-10011010-1-2
Max (°C)78910109888877
Min (°F)272830323234343234323028
Max (°F)454648505048464646464545

The rainy season runs from May to October, and July and August are the rainiest months, but with these temperatures it can snow even in summer. Here is the average precipitation.
Average precipitation - Nev. de Toluca
Nev. de TolucaJanFebMarAprMayJunJulAugSepOctNovDecYear
Prec. (mm)151515601152052402302109025151230

The three highest volcanoes of Mexico, Citlaltépetl, Popocatepetl and Iztaccihuatl exceed 5,000 metres (16,400 ft), and perennial glaciers are found at the highest elevations.

When to go

To explore the northern regions of Mexico (coasts and deserts), October is a good month, and in general spring and autumn are the most advisable (March-April and September-October).
Even in the tierras frìas, spring and autumn are preferable, but here the main purpose is to avoid the summer rains, rather than the heat: here you can also avoid September, which is still a rainy month. The tierras frìas can be visited also in winter, bearing in mind that it can get cold at night.
The tierras calientes can be visited preferably from December to February, to avoid both the heat and the rains of summer, and because in some areas the months of October and November are still very rainy. In spring, in April and May, the rains have not arrived yet, but the weather is usually hot.

As regards the sea, for a beach holiday the southern coast (see Acapulco) is warm and sunny in winter (eg Christmas and New Year), with a warm sea, around 28 °C (82 °F). In Acapulco the good season is long, from November to April.
The coasts of the Gulf of Mexico and Yucatán (see Veracruz, Cancun), during winter do not have an ideal climate, at least for a beach holiday: the sky is often cloudy, sometimes it can rain, and the Norte can lower the temperature. So the spring is better, from March to May, with a preference for April: in March sometimes some cool air can still arrive, especially in the first half of the month, while in May it begins to get hot, with the first thunderstorms.
Spring is fine also in Cabo San Lucas and the southern part of Baja California. In the northern coast of Baja California, where the air is mild even in summer, in this season you can sunbathe, even though the water is a little cold.

What to pack

In winter: for the Chihuahuan desert and the mountains, warm clothes, jacket, hat, gloves. For Baja California, eastern plains and tierras templadas, clothes for spring and autumn. For Mexico City and tierras frìas, clothes for spring and autumn during the day, warm jacket, wool cap for the evening. For the tierras calientes, light clothing, a sweatshirt for the evening in Yucatan and Riviera Maya; for the reef, equipment for snorkeling, water shoes or rubber soled shoes. For the highest mountains, warm clothes, down jacket, gloves, cap.

In summer: light clothing, sunglasses, sunscreen, a light raincoat. For the Chihuahuan Desert, a sweatshirt for the evening. For Mexico City and tierras frìas, sweatshirt or sweater for the evening, a jacket and umbrella. For the highest mountains, warm clothes, warm jacket, wind jacket, gloves, hat, hiking shoes.