Biscayne National Park in May: Weather, Sea Temperature and Rain Days

BISCAYNE NATIONAL PARK · MAY · FLORIDA

By May the bay off Biscayne National Park runs at 83.0°F at its daily peak, warm-bath water for a park that is almost all water. On shore, the Miami station NOAA uses for its normals logs an average high of 86.7°F, and on May 15 the sun stays up until 8:00 pm.

The trade-off shows up in the rain gauge: 6.32 inches in an average May, against 3.36 in April. That is still well short of June’s 10.51 inches, and your trip lands before hurricane season opens on June 1, as our Florida overview explains.

On this page

• Biscayne weather in MayHighs of 86.7°F, lows of 73.4°F and 6.9 rain days
• Can you swim in Biscayne in May?Sea at 83.0°F, measured as daily maxima
• How busy and how pricey is May?Booking, lodging tax and the boat budget
• Things to do in Biscayne in MaySnorkeling in 83.0°F water and the island keys
• A two-day Biscayne itineraryTwo days built around a 6:33 am sunrise
• May vs April and JuneHow the three months compare on heat, rain and sea
• Is May a good time to visit?Who May suits and who should shift to April

Getting to the park, the island landings and the rest of Florida’s parks stay the same all year. Our Florida national parks guide covers them, and getting around Florida covers the drive south from Miami.

Biscayne National Park weather in May: average highs, lows and rain days

NOAA’s National Centers for Environmental Information publish the 1991-2020 normals we use, from station USW00012839 in Miami: an average May high of 86.7°F, an average low of 73.4°F and 6.32 inches of rain. It is a station normal, read off a real thermometer. Every figure here comes from that Miami station, immediately north of the park, while the park itself is almost all water. Open water swings less than a city in both directions, so out on the bay expect afternoons a touch softer and nights a touch less cool than the Miami numbers.

Measurable rain, 0.10 inch or more, falls on 6.9 days in an average May: roughly one day in four or five. On 1.9 of those days the gauge reaches an inch or more, so a typical May brings about two real soakers. For a trip of two or three nights, most days should give you dry hours, with a fair chance of one wet spell. Put the boat outing on the day with the better forecast and keep the other for the mainland.

Between the 86.7°F afternoon and the 73.4°F night sits a gap of 13.3°F, and even the low stays warm. Pack for heat at both ends: breathable long sleeves and a hat for the boat, reef-safe sunscreen, a light rain shell for the wet days, and a dry bag for your phone and car keys. Leave the fleece at home.

On May 15 the sun rises at 6:33 am and sets at 8:00 pm Eastern Daylight Time, converted from sunrise-sunset.org’s 10:33 and 00:00 UTC. That makes about 13 hours 27 minutes of daylight. From the mainland shore the sunrise comes up over the bay to the east, and the evening light fades behind you over the land at 8:00 pm.

Can you swim in Biscayne National Park in May? Sea temperature and what it feels like

Open-Meteo’s Marine API puts the sea surface off Biscayne National Park at 83.0°F in May, averaged over 2015-2024. The figure is a mean of daily maxima, the warmest reading of each day, so it runs a shade warmer than a 24-hour mean would. It also comes from a different source and a different period than the NOAA air normals, so we attribute it separately.

In practice, 83.0°F sits only 3.7°F under the average May high, so wading in on a hot afternoon feels like stepping into a pool that has sat in the sun. April’s water, at 79.6°F by the same API, runs 3.4°F cooler. Expect early-morning water to read a little under the daily peak, and bring a rash guard for long snorkels: it covers both sun and any chill.

We could not read wind or wave data for Biscayne in May, so we give no figure for chop or swell. Check the National Weather Service marine forecast for Biscayne Bay the evening before a boat day, and book seats you can move if it turns rough.

How busy is Biscayne National Park in May? Crowds and prices

We found no occupancy series and no monthly room rates for Biscayne, so we crown no month cheap or expensive. The calendar does give a position: May falls just after Florida’s November-to-April dry season (National Weather Service, via our Florida overview) and just before hurricane season opens on June 1.

We could not verify how far ahead May rooms or boat trips fill, so we name no number of weeks. Rain shapes the booking more than the lead time: with 6.9 wet days in an average May, a refundable room and a boat seat you can shift by a day matter more than an early confirmation. Our Florida flights guide sorts the airports, and where to stay in Florida covers the bases.

We could not verify the lodging-tax rate that applies to rooms near the park, so we give no percentage. Look at the final price screen before you pay, and use our Florida trip-cost guide for the other lines of a vacation budget.

Nearly all of the park is water, and its keys, reefs and wrecks lie out in the bay. A guided trip or a private charter is what turns a shoreline visit into a day at Boca Chita Key or over the reef, and that is where extra money changes a May trip. We could not verify May fares for either. Spend first on flexibility: with 1.9 days of an inch or more of rain in an average May, pick the seat you can move over the cheaper one you cannot.

Things to do in Biscayne National Park in May

Warm water and long days arrive together in May: the bay averages 83.0°F at its daily peak and the sun stays up 13 hours 27 minutes on the 15th. A snorkel can stretch into a morning-long session, and there is light left for a second outing once the midday heat eases.

On the mainland, the Dante Fascell Visitor Center at Convoy Point is the park’s front door and a good spot for the 6:33 am sunrise over the bay. Out on the water sit Boca Chita Key, with its ornamental lighthouse, and Elliott Key, the park’s biggest island. Stiltsville’s houses stand on pilings in the flats, and the Maritime Heritage Trail links shipwreck sites for snorkelers and divers. Check the National Park Service site for current hours, fees and boat schedules before you go.

Ashore, the 86.7°F average high at the Miami station sets the pace of a May day, while the bay stays near 83.0°F at its daily peak. Open water swings less than the city, so the keys should feel a little milder than the station reads. Shade is scarce on a boat and on the island docks, so plan the exposed hours for morning and late afternoon.

We could not confirm entrance, dock or camping fees for May in our sources, so we list nothing as free. The National Park Service site above is the one to check before you drive down.

Biscayne National Park in May: a two-day itinerary

Be at Convoy Point by 6:15 am on day one for the 6:33 am sunrise over the bay. Get on the water by mid-morning, before the afternoon climbs toward its 86.7°F average, and snorkel or paddle until about noon. From noon to around 3 pm, stay in shade or indoors at the visitor center, after checking its posted hours. Head out again around 5 pm for a shorter session, and stay on the shore until the light goes at 8:00 pm.

Hold day two as your spare. With 6.9 wet days in an average May, move the island or reef trip here if day one’s forecast looked worse, and keep the same early start. If rain sets in for the day, switch to the mainland: the Everglades lie a short drive west of Homestead with boardwalk trails, and Miami sits north up the road.

Biscayne National Park in May vs April and June

April averages 83.6°F by day and 69.8°F at night, May 86.7°F and 73.4°F, June 89.3°F and 76.3°F, all from the same NOAA station and 1991-2020 period. Rain climbs faster than heat: 3.36 inches over 4.3 days in April, 6.32 over 6.9 in May, 10.51 over 12.6 in June. The Open-Meteo sea figures, daily maxima again, run 79.6°F, 83.0°F and 85.4°F.

Going four weeks earlier gives you 2.6 fewer rain days, 2.96 fewer inches and afternoons 3.1°F cooler, and costs you 3.4°F of sea temperature. Going four weeks later adds 2.4°F to the water and 2.6°F to the afternoon, along with 5.7 more rain days, 4.19 more inches and the opening of hurricane season on June 1. Our best time to visit Florida guide lays out the wider calendar.

Is May a good time to visit Biscayne National Park?

Yes, for swimmers, snorkelers and paddlers who want warm water and can keep one day flexible: May gives 83.0°F sea and fewer than seven rain days on average. No, for anyone whose trip hangs on a single fixed boat date, or who wilts in heat: afternoons average 86.7°F at the Miami station, and a typical month brings about two days of an inch or more.

If the answer is no, go in April. Its 4.3 rain days and 3.36 inches make a fixed boat date safer, its 83.6°F afternoons are easier on shore, and the water still reaches 79.6°F at its daily peak. Biscayne in April has the details.

Of the three months, only May pairs sea above 80°F with fewer than seven rain days in an average month.

The last word

Pick May for the water and hold one day in reserve for the boat. Then go early on the first morning. The bay’s 83.0°F daily peak sits 9.6°F above May’s average low of 73.4°F, so when you slip in near the 6:33 am sunrise, the water carries far more of yesterday’s warmth than the air around you.

Sources & data for this guide

• May, April and June air normals (highs, lows, precipitation, rain days) · NOAA NCEI 1991-2020 monthly normals, station USW00012839, Miami · checked Sep 24, 2026
• Station scope · the thermometer is in Miami, immediately north of the park, and open water swings less than a city, so conditions on the bay run a little milder at both ends · checked Sep 24, 2026
• Sea surface temperature, April to June · Open-Meteo Marine API, mean of daily maxima 2015-2024, a shade warmer than a 24-hour mean · checked Sep 24, 2026
• Sunrise, sunset and daylight on May 15 · sunrise-sunset.org, UTC converted to EDT · checked Sep 24, 2026
• Park places, hours and fees · National Park Service, Biscayne · we could not verify May hours, fees or boat fares, so we give none
• What we could not find · occupancy series, monthly room rates, the local lodging-tax rate, booking lead times and May wind or wave data. We rank no month by price and give no figure for any of these. Place descriptions are editorial · check operators when you book.

To plan your stay

• Best Time to Visit Biscayne National Park: Month-by-Month Weather, Sea Temperature and the Month to Skip
• Biscayne National Park in April: Weather, Sea Temperature and Rain Days
• Biscayne National Park in June: Weather, Sea Temperature, Rain Days and Crowds
• Biscayne National Park in March: Weather, Sea Temperature and Crowds

Nearby places

• Big Cypress National Preserve: Dark Sky Park, Swamp Buggies and the $100 ORV Permit
• Miami Travel Guide: Miami or Miami Beach, Neighborhoods, Beaches and Getting Around Without a Car
• Fort Lauderdale Travel Guide: State Park Beaches, FLL and the 12% Hotel Tax