Weather in Guanacaste in May

How May compares

May is the 3rd warmest month of the year in Guanacaste and ranks 9th of 134 destinations we compare for May - see where else is hot in May. Against London's average high of 16.6°C in May, Guanacaste is 14.8°C warmer by day and 15.3°C warmer at night.

Daytime and night-time in May

The typical May day in Guanacaste peaks at 31.4°C, but that is an average: the warmest 10% of days reach 34.3°C or more. About 99% of days top 25°C and almost every pass 30°C. Nights average 23.6°C; one night in ten drops to 22.4°C or lower, so pack a layer for evenings. Between 1991 and 2020 the hottest May day here reached 37.2°C (2019-05-09) and the coldest night 20.5°C (2013-05-08).

Rain in May

Wet (more than 8 rainy days): about 18 days with 1 mm or more, 245 mm in total. Year to year it varies a lot - the wettest May was 1993 with 560 mm, the driest 2015 with 28 mm. Humidity averages 78%, which makes the heat feel heavier than the thermometer suggests.

Sea temperature in May

The sea averages 28.9°C - warm enough to swim (22°c+). Depending on the year it ranges from 28.3°C to 29.5°C. This is the warmest the sea gets here all year.

Sunshine and daylight

Around 2.6 hours of sunshine a day (estimated from cloud cover), 12.5 hours of daylight: the sun rises about 05:20 and sets about 17:56 local time in mid-May. Average cloud cover is 79%.

Is May a good time to visit Guanacaste?

It is a reasonable choice: hot days but expect showers. The best months for Guanacaste on our scoring are February, January, December; months averaging 25°C or more: Jan, Feb, Mar, Apr, May, Jun, Jul, Aug, Sep, Oct, Nov, Dec.

Hot days, warm nights and an easy sea temperature

The heat is dependable: 75% of days reach 30°C, while hotter days can reach 34°C or more. With humidity at 78%, this is weather for loose, light clothing and a slower pace, particularly around midday. Plan shade breaks rather than packing your day with sustained outdoor activity. Evenings offer limited relief, so breathable nightwear and accommodation with effective cooling are sensible priorities. The sea averages 29°C, making swimming a comfortable temperature choice rather than a bracing dip, though warmth alone does not tell you about local swimming conditions. May is a good fit if you enjoy tropical heat; it is less suitable if you need cool evenings to feel comfortable.

The catch is rain and limited sunshine

May is wet, and the sunshine average is only about 2.6 hours a day despite 12.5 hours of daylight. That distinction matters: there is plenty of daylight for flexible plans, but you should not equate it with bright beach weather. Around 18 rainy days means waterproof protection for your belongings and a lightweight rain layer deserve space in your luggage. It does not mean every wet day is a complete washout, but neither should you assume rain will conveniently miss your outdoor plans. Choose May if swimming and warmth matter more than clear skies. If your main aim is dependable sunbathing, the balance of heat, rain and cloud makes this a less convincing choice.