When to visit the Andamans, and what the sea is doing

Most advice about when to visit the Andamans is written for somebody lying on a beach. If your day involves getting on a boat, the useful question is not "will it rain" but "will the sea let us go out".

Those have different answers, and the second one decides whether a trip happens.

The shape of the year

The islands take rain from both monsoons, which is why the wet part of the year is long. Roughly 3,000 mm falls annually, across about 156 rainy days.

January to April — the dry months. January averages around 35 mm of rain, February around 20 mm, March around 10 mm. This is the settled part of the year: calmest seas, most reliable sailings, clearest water. Mid-January to the end of February is the best of it.

May to September — the southwest monsoon. The heavy half. June is the wettest month at roughly 455 mm, August around 425 mm, May around 345 mm. Wind and swell come with it, and that is what closes a bay rather than the rain itself.

October to December — the northeast monsoon. Wetter than the dry season, gentler than the southwest. Rain tapers through November and becomes rare by December, which is why December feels like the start of the season even though the numbers say it is the end of the wet one.

Two windows where the weather turns

Tropical cyclones can form between April and December, with two peaks: late April to late May, and October to early December.

That is worth knowing because both sit at the edges of what people book. A late-April trip and an early-December trip are both usually fine and are both the ones most likely to lose a day to weather.

What this means for a day on the water

• The sea decides, not the forecast. A bright morning with a two-metre swell is a cancelled departure. A grey one with a flat sea is not.
• March and April are hot. Comfortable in the water, heavy out of it.
• The water is warm all year — 28 to 30 °C, warmest around April. Nobody cancels a dive in the Andamans because the sea is cold.
• A cancelled day is not a wasted trip if you leave slack. Operators reschedule around weather constantly. A three-day stay with one thing booked on each day has no room to absorb that; the same three days with two things booked does.

The short version

• Want the most certainty: mid-January to February.
• Want fewer people and will accept a lost day: December, or March.
• Travelling June to September: go with the expectation that the sea will decide some of your itinerary, and plan a trip that survives that.

Nothing here is a forecast. It is the pattern the year usually follows, which is what you plan against — and then you check the actual sea state the week you travel.