Weather in September — Sebastian, Florida

September in Sebastian is still hot and wet, with a normal high of 88.4 degrees, a low of 73.4 and 7.04 inches of rain at the Vero Beach airport station, NOAA's climate site for the area.

The month marks the first real step down from summer in Sebastian. The September daily normals have the high falling from 89.6 degrees on September 1 to 87.1 on September 30, a drop of two and a half degrees, while the overnight low eases from 73.7 to 72.4. The monthly mean in the NOAA NCEI normals is 80.9 degrees, about the same as June. Days of 90 or warmer fall to an average of 9.4, less than half of August's count, according to NOAA's threshold-day normals.

Rain stays heavy. September at Vero Beach averages 9.7 days with a tenth of an inch or more, the highest count of the year, and 1.9 days with an inch or more. One September in four brings less than 4.83 inches and one in four brings more than 8.45. North of Micco, the Melbourne airport normals make September the wettest month of all at 7.63 inches, with a high of 87.6 and a low of 73.7.

Yes, the National Hurricane Center puts the climatological peak of the Atlantic hurricane season on September 10, so September is the month of greatest tropical risk for Sebastian Inlet and the Indian River County coast.

The National Hurricane Center climatology defines the season as June 1 to November 30 and states that most activity occurs between mid-August and mid-October, with September 10 at the center of that window. That timing shows up in the Vero Beach record: the wettest September on file is 2004 at 23.01 inches, the month two hurricanes crossed the Treasure Coast, against a driest September of 1.67 inches in 1988, per the NWS Melbourne September 2026 summary.

Peak season does not mean a storm every year. In September 2026 the heaviest single rain at Vero Beach was 2.28 inches on September 6 and 7, well short of the multi-day totals that tropical systems have produced. The point for Sebastian is exposure: the warmest ocean water of the year sits offshore in September at the same time the Atlantic is most active.

Hurricanes Frances and Jeanne both struck the Treasure Coast in September 2004, three weeks apart, and Jeanne brought a 101 knot peak wind and a closed Sebastian River bridge to the city.

Frances came first. The Weather Prediction Center states that its center reached Sewall's Point on September 5, 2004 as a Category 2 hurricane. The NWS Melbourne report on Frances describes erosion of the western bank of the Indian River in southern Brevard and Indian River counties and the closure of part of the northbound lane of U.S. 1 north of the Sebastian River because of the risk of undermining.

Jeanne followed on almost the same track. According to the Weather Prediction Center summary of Jeanne, the center of its 50 nautical mile eye crossed the coast at the southern end of Hutchinson Island just east of Stuart at midnight on September 25, 2004, with estimated landfall winds of 120 mph. The NWS Melbourne Jeanne report lists a peak wind of 101 knots at Sebastian, about 116 mph, and a separate Sebastian gauge that recorded 92 knots before its anemometer failed. The report states that the Sebastian River bridge was damaged by erosion and closed for at least a week, and that severe erosion occurred all along the west bank of the lagoon in Indian River County.

Later Septembers were gentler on the city. On September 12, 2017, Sebastian Daily called Hurricane Irma the biggest hurricane threat to Indian River County in decades and reported that Sebastian, Fellsmere and Vero Beach were spared, with minimal or no damage to most homes. In September 2022, the same paper reported roads beginning to flood in Sebastian, Fellsmere and Vero Beach as tropical storm conditions from Hurricane Ian reached Indian River County.

September 2026 at Vero Beach was close to normal, with an average high of 88.7 degrees, 6.63 inches of rain and a 48 mph gust on September 7, according to NWS Melbourne.

The September 2026 report, issued on October 1, 2026, records a high of 94 on September 5 and a low of 63 on September 27. Thunderstorms were logged on 17 days. The September records for Vero Beach are a high of 97, set on September 5 and 6, 2019 and on September 17, 1996, and a low of 61 on September 29, 2006.

During a September storm threat, the City of Sebastian points residents to its own storm information line, 772-581-0111, to Indian River County Emergency Services at 772-226-3900, and to the National Hurricane Center.

The city's Tropical Weather Information page gathers the official channels in one place: the city's Facebook page and COStv channel, the Sebastian Police Department, Indian River County Emergency Services, the National Hurricane Center, Florida 511 and the state's Florida Emergency Information Line at 800-342-3557. For outages it lists the Florida Power and Light reporting number, 1-800-468-8249, and notes that reports help the utility track outages after a storm.

Radio is part of the Sebastian list as well. The page names eleven local stations, among them WQCS-FM 88.9, WSCF-FM 91.9 and WAVW-FM 92.7. The same page links the city's flood maps, a floodplain management report and a real-time water level gage, the records that matter most in September, when the Vero Beach rain normal is 7.04 inches and the Indian River Lagoon shoreline along Indian River Drive is exposed to tropical surge.

September brings the warmest offshore water of the year near Sebastian, 84.0 degrees at the Canaveral buoy, before the dry season and cooler fronts arrive in mid to late October.

The NOAA NCEI Coastal Water Temperature Guide lists September averages of 84.0 degrees at the Canaveral 20 NM buoy, 87.0 at Trident Pier and 85.1 at Lake Worth Pier. For the shallow nearshore pier site, September is the warmest month on the table. The ocean off Sebastian Inlet State Park is now warmer than the 80.9 degree mean air temperature at Vero Beach, and stays warmer through the winter.

Warm September water coincides with the second half of the sea turtle year on the beaches east of Sebastian. On the Archie Carr National Wildlife Refuge, the Fish and Wildlife Service writes that nesting decreases in the fall while the hatchlings are just getting started, and it pairs that season with the peak of hurricane season, when storms typically peak in August and September.

Two seasonal markers close out the month. The Indian River County fertilizer ordinance blackout, which bars fertilizer from June 1, ends after September 30. And the rainy season starts to fade: NWS Melbourne's season onset study puts the median start of the dry season at Vero Beach on October 19, so late September in Sebastian is the tail of the wet season rather than its end.