One year, four calendars
Baja California Sur does not follow the simple rains-and-drought calendar of most of Mexico; it runs on four overlapping calendars that rarely match what visitors imagine from outside. There is the whale calendar, as grey whales arrive from the North Pacific to calve in sheltered lagoons; the hurricane calendar, which tracks the tropical Pacific from August to October; the wind calendar, which turns the gulf into a kiteboarding ground between November and March; and a short window, tucked almost invisibly between the other three, when the weather is simply pleasant, with no caveats attached.
La Paz is the most sensible base for working around any of these calendars, since it avoids the extreme heat of Los Cabos and the direct hurricane exposure of the east coast, and it works as a launch point for the whales, the gulf islands and the inland towns. Choosing when to go to Baja California Sur is not a question of high season versus low season, as in the Caribbean, but of knowing what exactly you want to see or do, because the perfect month for swimming with whale sharks is not the perfect month for diving, nor the one with the best wind.
The calendar, month by month
The year is best understood as a wheel of four bands that overlap far more than they seem to at first glance. Grey whales reach Guerrero Negro and Magdalena Bay in December and stay until April, with births peaking in February; whale sharks show up in La Paz Bay from October to April, almost tracing the whale calendar but in the gulf rather than the Pacific. Strong El Norte wind dominates November to March around La Ventana and Los Barriles, and the inland heat begins in May and does not ease until October.
The perfect band — no strong wind, no extreme heat, no hurricanes — fits almost entirely between mid-April and early June, and again, more briefly, in November, once the cyclones have passed and before the wind fully returns. Outside those weeks something always has to give: watching whales in January means accepting that season's wind, diving in summer means accepting inland heat that tops 38°C, and travelling in September means accepting the real risk of a cyclone closing the trans-peninsular highway for days at a time. No single month has it all; each month simply suits a different priority.
Why the water and the air never agree
Water and air in Baja California Sur almost never agree, and that changes what is worth planning around each month. In deep winter, with the air cool and pleasant by day, the sea can drop to temperatures uncomfortable for swimming without a wetsuit, especially on the Pacific side. In deep summer the opposite happens: the gulf water warms to something close to bathwater, perfect for swimming and diving, while the inland air becomes almost unbearable during the day. No month delivers both things comfortably at once, and that is worth knowing before packing a wetsuit or a beach towel.
For diving and snorkelling, what matters is not the tourist calendar but the water temperature, and there the Sea of Cortez behaves differently from the open Pacific: it warms earlier in spring and cools later in autumn, so August and September usually bring the warmest water of the year to La Paz, even though they overlap with the land heat and part of hurricane season. Anyone who wants to swim comfortably without a wetsuit should look at those months; anyone who wants to walk or wander through inland towns without sweating should look at December and January, even though the sea will feel cooler than expected then.
Whales, hurricanes and wind, in detail
The whale season is the most predictable of the four, and also the one that best organises an entire trip. Grey whales arrive from Alaska to calve in the sheltered Pacific lagoons — Ojo de Liebre, Guerrero Negro, Magdalena Bay — between December and April, with births peaking in January and February, when the odds of a close encounter from a panga are highest. The water in those lagoons is cold and the surrounding desert air is pleasant, so it is worth packing a jacket for the boat trip and light clothes for the rest of the day, something that surprises anyone expecting tropical heat.
Eastern Pacific hurricanes follow a fairly regular pattern: the official season runs May to November, but the real risk of a system making landfall on the peninsula concentrates in August, September and October. Wind, by contrast, is not an emergency-season event but a daily one: El Norte blows hard from November to March in the gulf, especially between La Ventana and Los Barriles, and while it draws thousands of kite and windsurf enthusiasts every winter, it also cancels panga trips and makes any small-boat crossing awkward during those months in that particular area.
The weeks that actually have it all
There are two short windows when almost nothing works against you at the same time, and both are brief, which explains why they book up fast. The first runs from mid-April to early June: the winter wind has already eased, the fierce summer heat has not yet arrived, hurricane season has not officially started, and the water is already warm enough to swim in without a wetsuit. The second, shorter one falls in November, once hurricane season has practically ended, the summer heat has dropped, and the strong El Norte wind has not yet fully settled in.
Those weeks are no secret: agencies, hotels and plenty of Mexican travellers know them just as well, so it is worth booking several months ahead if the trip falls in April, May or November, especially around long weekends or Easter. Outside those exact dates, the window stays reasonably good for about two weeks either side, though with somewhat more wind or heat depending on which end of the calendar you land on. Treating them as fixed, rigid dates is a mistake; treating them as a three or four week range gives far more room to find good pricing and good weather.
The mistakes people keep making
The most common mistake is treating Baja California Sur as a generic beach destination and booking on price alone, without checking which month it is. July and August are cheap because the interior is stifling and the Pacific already carries some tropical moisture, not because it is a well-kept secret. The second mistake is assuming Los Cabos and La Paz share a climate, when in fact Los Cabos concentrates more heat, more luxury hotel supply and higher prices in good season, while La Paz tends to run milder and considerably cheaper on the exact same dates.
The third mistake, and the costliest, is travelling in September trusting that a cyclone will not interfere, with no travel insurance and no slack in the itinerary. Hurricane season has a real peak in those months, and when a system makes landfall the trans-peninsular highway can close, flights get cancelled and coastal towns go without normal supply for several days. The fourth mistake is smaller but constant: underestimating the winter wind and planning diving or snorkelling by panga around La Ventana between December and March without checking the local forecast the day before, which changes the trip entirely in that area.
What people always ask
Six concrete questions about when to go to Baja California Sur, answered with the real year-to-year variation and without faking a precision that does not exist. They run from the most practical — which month suits which plan — to the most uncomfortable, which is accepting that no single month delivers perfect weather, low prices and no crowds all at once. Baja Sur forces a choice between two of those three things, almost never all three, and knowing that in advance avoids the disappointment of arriving expecting something no calendar, however carefully read, can fully promise.
One idea worth repeating does not fit in a short answer. Anyone chasing whales has to accept some wind; anyone chasing beach heat has to accept high prices and crowds in Los Cabos; anyone chasing quiet and a tight budget has to accept a sea cooler than expected. La Paz, thanks to its position and its somewhat milder climate compared with the rest of the peninsula, is usually where those three tensions balance best, which is why it works as a sensible base nearly all year round, even when no single month is perfect for absolutely everything a traveller wants to do.