Weather in Boston in May

A good month. May is a solid month to be in Boston. Highs average 19.1 °C, lows 8.6 °C, and rain falls on 12 days — nothing in the month is working against you.

May ranks 3 of 12 in Boston. Only September scores clearly higher, and the difference is small enough to be settled by price rather than weather.

Rain on 12 days, 3 of them heavy. Enough to need a plan B, not enough to need a plan around it. Nothing specialised needed — this is the month you pack for the trip rather than for the weather.

What the averages hide

Averages flatten a month, and this one hides a few things: it never really gets hot: not one day in an average May reaches 30 °C. Across the twenty years measured, the hottest May day reached 32 °C and the coldest night fell to -0.2 °C, and the wettest single day dropped 72 mm — roughly 76% of the month's rain in one day.

May is moderately variable: 36 mm in the driest year against 284 mm in the wettest, around an average of 95 mm. Roughly two Mays in three land near that average, and the third does something else entirely.

Wind is light at 1.6 km/h, so the temperature on the page is close to the temperature on your skin, and humidity runs at 79%, high enough to notice on the warm days without dominating them.

How May sits in the year

The month is on the way up: 5.9 °C warmer than April, and June adds another 4.8 °C. Late in the month feels noticeably different from the start of it, which is worth knowing if the trip is short.

Daylight in May

14.6 hours of daylight, gaining 1 hours across the month. That is between Boston's extremes of 15.3 and 9.1 hours, so days are long enough not to constrain the plan.

Sea temperature

The sea sits at about 9.3 °C in May — too cold to swim without a wetsuit. The sea peaks at 19.7 °C in August and bottoms out at 4.6 °C — water lags the air by a month or two, which is why the best swimming often comes after the best weather.

How busy it gets

Peak season. Expect the highest prices of the year and to be booking well ahead.

Crowd levels are estimated from climate desirability and school-holiday calendars, not from visitor numbers.

May in Boston versus nearby

If Boston is one option among several, the nearby comparison is worth making. New York City is the weaker option in May — 2.1 °C cooler, 1 day more rain. Bar Harbor is the weaker option in May — 5 °C cooler, 1 day more rain.

So: May works, with September the better month by 7 points if the dates can move. If they cannot, nothing here should stop you booking.

Every month in Boston

See all twelve months in Boston, or where else to go in May.