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Charleston Mosquito Forecast

Today's mosquito activity in Charleston, the week ahead, and what to do about it. Updated hourly.

Bite Index · Sunday, November 8

Moderate

Moderate mosquito activity in Charleston today: expect some bites at dusk.

Some bites at dusk and dawn, mostly near creeks, gardens and shade.

About normal for November in Charleston County.

  • Only 0.0 in. of rain Oct 21–Oct 30, so few new breeding sites; what's biting is coming from irrigation, pools and creeks.
  • It's the edge of the season; warm weeks like this one keep it going past the calendar.
  • A two-week average of 67°F keeps populations growing, just more slowly than midsummer.

The week ahead

Each day's Bite Index, from this week's weather and the rain that is still hatching. Forecast days get less certain as the week goes on.

  1. Today
    26Mod.70°/54°dry
  2. Mon
    26Mod.74°/49°dry
  3. Tue
    32Mod.73°/51°dry
  4. Wed
    28Mod.74°/59°dry
  5. Thu
    29Mod.73°/58°dry
  6. Fri
    16Low63°/46°dry
  7. Sat
    15Low56°/40°dry

Protect tonight

Worth repellent if you'll be outside at dusk or dawn.

  1. A botanical or 10% picaridin lotion covers a patio evening; reapply after about two hours.
  2. A fan on the patio does real work: mosquitoes are weak fliers and avoid moving air.
Which repellent, and how much: DEET vs picaridinBest natural repellents

Why Charleston's mosquitoes do what they do

Charleston is a peninsula between two tidal rivers with salt marsh and sea islands on every side, and its mosquitoes come off the marsh in waves after high tides and summer storms. Charleston County Mosquito Control treats by air and ground from spring through fall and stepped up surveillance after West Nile detections in 2026.

  • Salt marsh and sea islands: James, Johns and Wadmalaw Islands and the Ashley and Cooper marshes produce salt-marsh Aedes broods on every spring tide.
  • Flooding: the peninsula floods on king tides and heavy rain, leaving standing water in streets and yards.
  • Humid subtropical summers: dusk humidity is high from May through September.
  • Aerial control: the county sprays by air after big broods; its notices say where and when.

A typical year in Charleston County

The long-run mosquito index by month from our season map (NOAA climate normals plus effort-corrected sightings). Today's Bite Index is the live version of this; the month you're in is marked.

  1. JJanuary: 0
  2. FFebruary: 8
  3. MMarch: 28
  4. AApril: 50
  5. MMay: 70
  6. JJune: 89
  7. JJuly: 95
  8. AAugust: 100
  9. SSeptember: 95
  10. OOctober: 66
  11. NNovember: 34
  12. DDecember: 0

Local surveillance and West Nile virus

The Bite Index measures nuisance biting, not disease. Charleston County's health department traps and tests mosquitoes through the season and publishes positive West Nile pools by ZIP code. When your ZIP has an active advisory, follow it regardless of today's number.

How the Bite Index is scored

The index is a model of conditions, not a mosquito count. Four weather factors are combined on a 0–100 scale, then scaled by the season. Every factor and today's value for it is listed here so you can check the number yourself. It uses the same temperature curve and rain logic as our county-level mosquito season map, which has been validated against effort-corrected sighting data across 41 states.

BBreeding pressure

Rain 7–14 days ago (0.0 in. between Oct 21 and Oct 30). Eggs need water to hatch, and at summer temperatures the egg-to-biting-adult cycle takes about a week, so today's mosquitoes are last week's rain. Cool weather stretches the window; hot dry days shrink it as shallow water evaporates.

Weight 40%
Today 0%

DDevelopment

The trailing two-week average temperature, on the same curve as our national season map: nothing below 50°F, full speed at 78–88°F, a small penalty in extreme heat.

Weight 25%
Today 60%

ATonight's activity

Whether the population that exists will actually fly and bite this evening: dusk temperature (65–85°F is ideal), wind (they stop flying around 10 mph), humidity, and rain around sunset.

Weight 25%
Today 63%

GGround truth

A nudge from local trap counts and reports when we have them. For Charleston this is neutral today; the health department's surveillance is linked above and will feed this factor as we wire it in.

Weight 10%
Today neutral

SSeason gate

A multiplier from the calendar: fully open in the city's season months, half-open in the shoulder months, nearly closed in deep winter unless the week is warm. Below a 50°F weekly average the index is simply 0.

Weight ×
Today 60%

index = 100 × S × (0.40 × (0.2 + 0.8·B) + 0.25 × D + 0.25 × A + 0.10 × (0.5 + 0.5·G))

Bands: Low 0–20 · Moderate 21–40 · High 41–60 · Very High 61–80 · Severe 81–100. Weather is from Open-Meteo (observations and the 7-day forecast), refreshed hourly. The lag and temperature thresholds follow published work on Culex and Aedes development (Rueda et al. 1990; Cornell NRCC degree-day emergence; JAMCA 2024 on rainfall two to four weeks before trap peaks).

Questions people ask about mosquitoes in Charleston

When is mosquito season in Charleston?
March through November, peaking from June through September. Salt-marsh broods follow the tides, so a calm evening after a spring tide can be bad in any warm month.
Why are the mosquitoes so bad after a king tide?
Salt-marsh mosquitoes lay eggs on the mud at the marsh edge; a flooding tide hatches them all at once and a week later the adults fly inland. That's why the county's aerial treatments follow the tide calendar.
Is West Nile virus a risk in Charleston?
Yes. The county detected West Nile in 2026 and increased treatment and surveillance in response. Its notices are authoritative; follow them over the index.
Where does this forecast's data come from?
Open-Meteo weather for downtown Charleston, scored by our documented model and compared with Charleston County's season-map climatology. It does not include tide data.

Also covers Mount Pleasant, North Charleston, Summerville, James Island, Folly Beach, Isle of Palms, Daniel Island, Kiawah: the forecast point is central Charleston, and conditions within about 30 miles track it closely. Weather fetched Nov 8, 12:28 PM local time.

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