Weather in May — Sebastian, Florida

A normal May in Sebastian reaches 85.7°F in the afternoon and 67.8°F at night, with 4.20 inches of rain at the Vero Beach station, the largest monthly normal since October's 5.33 inches.

NOAA's 1991 to 2020 normals for Vero Beach, the station behind NWS Melbourne's Indian River County climate reports, put the May mean at 76.7°F, 4.6 degrees above April (NOAA NCEI monthly normals). Afternoons of 90°F or more average 4.5 days in May, nearly three times April's 1.6, and nights under 50°F almost vanish, at 0.1 per May.

May rain at Vero Beach is lopsided, which matters for Sebastian lawns, the St. Sebastian River and the lagoon. The NOAA normals place a quarter of Mays under 1.60 inches and a quarter over 4.84 inches. The extremes in the NWS Melbourne May report run from 0.09 inches in 2004 to 17.98 inches in 2016 (NWS Melbourne May 2026 climate report, IEM archive).

NWS Melbourne's study of wet season onset gives Vero Beach, the closest long record to Sebastian, a median start date of May 26, between Fort Pierce on May 25 and Melbourne on May 28.

The same NWS Melbourne table lists Stuart at May 23, Orlando and Sanford at May 27 and Daytona Beach at May 30, using records from 1950 to the present; the start date is a median, so half of years begin earlier and half later (NWS Melbourne wet and dry season onset). For Vero Beach, the dry season returns on a median date of October 19.

The engine of that change is the sea breeze. NWS Melbourne's lightning climatology says May brings a rapid increase in lightning across Florida, with the main contribution coming from thunderstorms that develop along the sea breezes (NWS Melbourne lightning climatology). NWS Melbourne puts the yearly count of thunderstorm days at 70 to 80 on the east coast around Melbourne and Vero Beach, the stretch that includes Sebastian, Roseland and Fellsmere, against 80 to 90 inland at Orlando (NWS Melbourne lightning statistics).

The onset dates step up the Treasure Coast past Sebastian from south to north. Stations to the south, Fort Pierce and Stuart, turn wet a day to three days earlier than Vero Beach, and stations to the north, Melbourne and Daytona Beach, two to four days later. The cooler season begins later in the fall at Vero Beach too, with the first reading below 60°F arriving on a median date of October 22.

Ocean water near Sebastian passes 80°F at the beach in May, with Trident Pier averaging 80.2°F, while the Canaveral buoy offshore averages 77.4°F.

Lake Worth Pier, the next station south of Sebastian Inlet, averages 80.3°F in May, almost identical to Trident Pier to the north (NOAA Coastal Water Temperature Guide). The offshore Canaveral buoy gains 3.1 degrees from April, its largest monthly gain so far in the year, and the gap between pier and buoy shrinks to 2.8 degrees.

May is the first month on NOAA's averages when all three stations that bracket Sebastian Inlet State Park and Wabasso Beach sit at or above 77°F. Offshore, the Canaveral buoy then stays above 77°F through November, when it averages 78.7°F.

Both recent Mays ran hot and short of rain at the Vero Beach station that serves Sebastian: May 2026 logged 12 days at 90°F or above and May 2025 logged 15, against a normal of 4.5.

May 2026 at Vero Beach averaged 80.1°F, 3.4 degrees above normal, with highs of 94°F on May 2, May 9 and May 31 and average lows 4.5 degrees above normal at 72.3°F (May 2026 report). Rain totaled 2.53 inches, 1.67 below normal, and no single day reached an inch. Thunder was recorded on 7 days, and the strongest gust, 42 mph from the north, came on May 11.

May 2025 at Vero Beach was hotter at the top, reaching 96°F on May 21, and drier, with 2.08 inches of rain, 2.12 below normal (NWS Melbourne May 2025 climate report, IEM archive). Its mean of 79.8°F ran 3.1 degrees above normal, and it logged thunder on 8 days. The record May high for the station remains 99°F, set on May 29, 2000.

The two Mays differed more at night than by day in Sebastian's records. May 2026 bottomed at 63°F on May 7 and May 8, and May 2025 at 65°F on May 6. Average relative humidity at Vero Beach was 74 percent in May 2026, with fog on 14 days, and the station averaged 9.6 mph of wind, against 8.6 mph in May 2025.

May storm risk in Sebastian centers on lightning and severe thunderstorms, and NWS Melbourne's storm surveys include EF1 and EF0 tornadoes in Indian River and St. Lucie counties on May 17, 2016.

Lightning grows quickly. NWS Melbourne estimates about 838 cloud to ground strikes in Brevard County, Sebastian's northern neighbor, in a typical May, against about 576 in April, and its Florida lightning death table counts 29 deaths in May across the years it covers (NWS Melbourne lightning statistics). Other May entries in the survey list include a hail event across east central Florida on May 21, 2020 (NWS Melbourne storm surveys). The list also records a May 24 to June 6, 2020 heavy rain and flash flood event in coastal Martin County, south of Sebastian and the Treasure Coast inlets.

May is the last month before hurricane season. The Atlantic season runs from June 1 to November 30, and the National Hurricane Center notes that the first named storm typically forms in mid to late June (National Hurricane Center climatology). The City of Sebastian posts information about any hurricane or tropical storm on its Tropical Weather Information page (City of Sebastian).