The short version, by traveller
Los Cabos has genuinely distinct seasons, and the right month depends more on what you came to do than on any general notion of 'good weather'. The desert climate means the days are almost always sunny; what changes is the sea, the crowds, the price and the storm risk.
- Here for whales: 15 December to 15 April, ideally February.
- Here to swim and snorkel: July to October, when the sea is 81–84°F.
- Here for value with no compromise: late April, May, or the first three weeks of November.
- Here to fish: October for the tournament season, or the winter months for cheaper striped marlin.
- Here to avoid crowds and pay the least: August, if you accept the storm risk.
High season: December to March
This is the peak, and it earns the label. Rainfall is effectively zero, daytime highs sit between 79°F and 82°F, and the regulated whale season runs from 15 December. It is also when hotel rates are at their annual maximum and the better restaurants need reservations days out.
Two caveats matter. The sea is at its coldest of the year, 72–73°F in February and March, which is cool enough that most snorkellers want a shorty wetsuit. And March brings spring break, which changes the character of downtown Cabo San Lucas and Medano Beach for roughly three weeks.
Shoulder season: April, May, October, November
This is where the value is. April holds the winter weather without the winter price — and the first two weeks still fall inside whale season. May is dry, warming, and quiet. Late October and November recover from the storm season with an 81–83°F sea and reliable sun.
November in particular is arguably the strongest all-round month in Los Cabos: hurricane season closes on 30 November, the sea is still warm from summer, days are 86°F, and the first whales appear ahead of the official season. The one thing to plan around is US Thanksgiving week, when rates briefly jump to peak levels.
Low season: June to September
Summer is hot — 92–93°F days with humidity that builds from July — and it carries real hurricane exposure. The upside is an 81–84°F sea, the best snorkelling and diving water of the year, and rates that can be half of February.
September is the exception we would tell anyone to skip. It is the wettest month at 3.1 inches, the historical peak of hurricane activity, and enough restaurants and small hotels close that the town feels shuttered. If you do travel in the summer, buy insurance that covers named storms and get every operator's weather-cancellation policy in writing.