Charleston Harbor holds onto summer warmth in the fall tide swing

What's next

Expect the harbor to hold in the high 70s through the next few days. Late-September water temperatures this far south typically don't break toward the mid-70s until closer to mid-October. With the moon in a waning gibbous phase, tidal ranges are moderating off the recent full-moon peak but still delivering solid current on both the ebb and flood, worth planning around the mid-morning high and the mid-afternoon low if you're targeting spots that only fish well on moving water.

The better window this week looks like the two to three hours surrounding each tide change, when current is strong enough to stack bait without making boat positioning a fight. Weekend conditions should track closely with today's pattern barring a shift in the marine forecast, so the tide table is the more reliable guide right now than the calendar.

Context

Late September in Charleston Harbor sits squarely in the fall transition — water still carrying summer heat while day length and air temperatures pull back. That lag between air and water cooling is typical for the South Carolina coast this time of year, and 78°F is consistent with where local waters usually sit through early October before a more decisive cool-down arrives. Nothing here points to an early or late season; conditions are tracking a normal seasonal clock.