Photo: US Government · Public domainMidwinter lows in Harbor Island stay above those of 90% of U.S. towns
In July the day’s top temperature is typically 90°. August is the wettest month, November the driest. Its yearly precipitation tops that of 79% of U.S. towns. The frost-free window for a garden runs roughly March 1 to December 6.
A year in Harbor Island at a glance
Each month’s typical high and low, and what it brings.
What stands out about Harbor Island’s climate
Compared with towns across the U.S., with Harbor Island’s place in South Carolina beside it.
What a year in Harbor Island feels like
Typical highs and lows by season and by month, from NOAA’s 30-year normals.
About 280 frost-free days a year
In half of years the last 32° night comes by March 1 and the first by December 6. Frost and day counts come from NOAA’s station at Edisto Beach Sp, SC, 11 miles from the town’s center, at about the same height.
The 2023 USDA map puts Harbor Island’s center in zone 9b: the coldest night of a typical winter, averaged over 1991–2020, reaches about 26°. Plant labels use the zone; frost dates tell you when to plant.
Freezing nights by month
Average nights at or below 32°
90° days by month
Average days at 90° or more
About 49 inches of rain a year
August is the wettest month and November the driest. Rain falls on about 118 days a year. Snow is rare: about 0.0" in a normal year at Beaufort Mcas, SC, so most winters see none.
Rain + melted snow by month
Inches of water
Heating and cooling a home in Harbor Island
48% of the work is heating, so air conditioning is the bigger bill. Months averaging under 55° run from December through February.
Degree days add up how far each day’s average falls below (heating) or rises above (cooling) 65° over a year. NOAA normals at Edisto Beach Sp, SC.
Living with Harbor Island’s climate
What the numbers mean for a garden, a free afternoon and a bad-weather day.
280 frost-free days in zone 9b. The last frost comes by Mar 1 in half of years, so many gardeners wait a week or two past that to set out tomatoes. The first fall frost comes by Dec 6.
Months with highs of 62–84° and lows of 40° or more: February, March, April, May, October, November and December. 0.0 miles of trails are waiting.
Parks & trails →Of the yearly building losses FEMA expects in Harbor Island from natural hazards, hurricanes are the largest share (66%); heat waves, cold waves, winter storms and ice storms together are 1%. Normals are averages; the hazards page covers the extremes.
Natural hazards →Harbor Island and similar climates
TownRatings has no climate map of the towns around Harbor Island yet.
Climates most like Harbor Island’s, farther away
TownRatings’ own comparison of NOAA 1991–2020 normals, not a NOAA product: places of 5,000+ at least 150 miles away, one per state, closest on January low, July high, precipitation and snow.
| Town | Jan. low | July high | Precip. | Snow |
|---|---|---|---|---|
| Harbor Island, SC | 41° | 90° | 49" | 0.0" |
| Moultrie, GA | 39° | 91° | 51" | 0.0" |
| Jacksonville, FL | 44° | 92° | 51" | 0.0" |
| Clute, TX | 46° | 91° | 50" | 0.0" |
| Phenix City, AL | 36° | 92° | 51" | 0.0" |
Temperatures and precipitation come from NOAA’s 5 km grid; snow and day counts from the stations named on this page.
Warmer than it used to be
The last 30 years in Harbor Island averaged 1.1° warmer than the 1900s. The biggest change is in December (+2.1°).
A smaller shift than in 73% of U.S. towns.
Change by month
The two periods overlap (1991–2000 is in both), which makes the gap a little smaller than it would be between separate periods.
How Harbor Island compares
Against 12,954 U.S. towns of 2,500 or more (one per 5 km climate cell), with Harbor Island’s place among South Carolina’s.
Harbor Island weather by month
Highs, lows and precipitation from NOAA’s grid at Harbor Island’s center; snow, wet days and snow on the ground from Beaufort Mcas, SC. 1991–2020 normals.
| Month | High | Low | Rain + melt | Snow | Wet days | Snow on ground | 30-yr range |
|---|---|---|---|---|---|---|---|
| January | 60° | 41° | 3.3" | 0.0" | 9 | 0 | 45° – 57° |
| February | 63° | 44° | 3.0" | 0.0" | 9 | 0 | 46° – 62° |
| March | 68° | 50° | 3.4" | 0.0" | 9 | 0 | 53° – 66° |
| April | 75° | 57° | 3.2" | 0.0" | 9 | 0 | 61° – 71° |
| May | 82° | 65° | 3.1" | 0.0" | 8 | 0 | 69° – 79° |
| June | 87° | 72° | 5.1" | 0.0" | 13 | 0 | 75° – 84° |
| July | 90° | 75° | 5.9" | 0.0" | 13 | 0 | 80° – 86° |
| August | 89° | 74° | 6.6" | 0.0" | 13 | 0 | 79° – 84° |
| September | 85° | 70° | 5.0" | 0.0" | 10 | 0 | 75° – 82° |
| October | 78° | 60° | 4.4" | 0.0" | 8 | 0 | 65° – 74° |
| November | 69° | 50° | 2.6" | 0.0" | 8 | 0 | 55° – 66° |
| December | 62° | 44° | 3.1" | 0.0" | 10 | 0 | 44° – 64° |
| Year | 76° | 59° | 48.7" | 0.0" | 118 | 0 |
How much a month can swing
A normal is an average. December swings the most: from 1991 to 2020 its average ranged from 44° to 64°. August is the most reliable, staying within 5°.
Where Harbor Island’s numbers come from
Normals are 30-year averages, not a forecast. How TownRatings reads climate data →
- Temperatures and precipitation: NOAA’s gridded 1991–2020 normals for the 5 km cell at Harbor Island’s center.
- Snow: Beaufort Mcas, SC.
- Frost, freezing nights, 90° and 100° days, heating and cooling: Edisto Beach Sp, SC, 11 miles from the town’s center, at about the same height; the nearest station that passes our checks for distance, height and agreement with the grid.
- Growing zone: USDA Plant Hardiness Zone Map, 2023. USDA Agricultural Research Service and PRISM Group, Oregon State University, prism.oregonstate.edu/phzm, accessed 8 Oct 2026.
- Then and now: NOAA’s gridded normals for 1901–2000 at the same cell.
- Storms and extremes: FEMA National Risk Index (expected annual losses to buildings).
Common questions about Harbor Island’s climate
What is the weather like in Harbor Island?
A typical July afternoon reaches 90°, a January night drops to 41°, and snow is almost unheard of. Milder January nights than 90% of U.S. towns; hotter July afternoons than 78% of U.S. towns.
How cold does it get in Harbor Island in winter?
January nights average 41°. About 15 nights a year reach 32° or below. In the coldest January of the last 30 years the month averaged 45°.
How much snow does Harbor Island get?
About 0.0 inches in a normal winter at Beaufort Mcas, SC, so most winters see none.
How hot does it get in Harbor Island?
July, with a typical high of 90° and a low of 75°. About 42 days a year reach 90° (Edisto Beach Sp, SC).
When is the first and last frost in Harbor Island?
In half of years the last spring frost (32°) comes by March 1 and the first fall frost by December 6, about 280 frost-free days, at Edisto Beach Sp, SC.
What growing zone is Harbor Island in?
Zone 9b on the 2023 USDA Plant Hardiness Zone Map: the coldest night of a typical winter reaches about 26°.
What is the best time of year to visit Harbor Island?
By one simple rule (highs of 62–84° and lows of 40° or more), February, March, April, May, October, November and December. The rule is ours, not NOAA’s; the month table has the numbers to judge by.
Is Harbor Island getting warmer?
Yes: 1991–2020 averaged 1.1° warmer than 1901–2000 on NOAA’s grid. A smaller shift than 73% of U.S. towns.
Neighbors talk weather
Gardens, snow, and the best days of the year in Harbor Island.
Source: NOAA NCEI U.S. Climate Normals, 1991–2020 and 1901–2000; USDA/PRISM 2023 hardiness zones; FEMA National Risk Index. Today’s forecast: National Weather Service.