Været i Puerto Vallarta (Vallarta) i september

Regulars call this a favorite month, warm and sunny by day with the air feeling noticeably less oppressive than the rainy summer stretch, evenings cool enough for a light sweater. Our row backs that warm, still-humid read, 29.8C reading as a hot 33C, over 19.4C nights, with rain minimal at 22.3mm across 3 days and humidity at 84 percent, real moisture in the air even if it's a real drop from summer's peak. Regulars are specific this marks the start of the humpback whale season in Banderas Bay, a real seasonal highlight beyond the weather itself. The sea sits at a warm 26.8C, cooling a touch from summer highs but still comfortably swimmable. The record: 9.6 hours of sun, a 7.8 kph wind and AQI 38.

January here has two fixed things about it. It is high season, effectively booked out, and it sits in the middle of the whale window - regulars date the humpbacks from about the 8th of December to the 23rd of March, which makes this the safest part of it. Their weather summary is 28 to 30C by day, and our column says 28.8C. What they warn about is the other end of the day: nights and early mornings want a light wrap, and our row has them at 17.9C, an eleven-degree fall. The sea is 25.3C, which they describe as cool but swimmable, and genuinely cold on a rare cloudy day. Rain is effectively over, 21.4mm across 2.6 days. The record: humidity 81 percent, 9.7 hours of sun, an almost still 8.3 kph wind and AQI 31.

May is the gap between two seasons and regulars value it for exactly that. The rains have not started - they arrive late May or early June and run to September - the heat has not reached its summer level, the crowds have gone, and the hotel rates drop from their high-season figures this month. The caveat is at the end: humidity starts building in the last weeks, and every week after that is worse. Our row shows the dry half plainly at 6.4mm across 0.9 days, with 32.1C reading as 37C and a 27.6C sea. Nights hold at 22.4C. It is usually breezy on the beach, and our 11.4 kph average says that breeze is light. The record: humidity 75 percent, 11.9 hours of sun and AQI 56.

February sits squarely inside the humpback season here, which regulars date precisely - roughly the 8th of December to the 23rd of March, with the whales in Banderas Bay through to April - and January reports describe breaching offshore all day. On weather they mostly say February is fantastic, with one dissenting account of a first week of heavy rain and the mountains lost in cloud; our row's 19.9mm across 2 precipitation days says the usual case is the dry one. The number worth checking before packing swimwear is the sea: 24.8C here, noticeably cooler than the Mexican Pacific further south, because this is a winter bay. The record: 29.3C reading as 33C, 18.1C nights, humidity 79 percent, 10.2 hours of sun and AQI 31.