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Tucson Mosquito Forecast

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

Bite Index · Sunday, November 8

Low

Mosquito activity in Tucson is low today.

Few mosquitoes. You may see one or two at dusk near water.

About normal for November in Pima County (typically around 7).

  • Only 0.2 in. of rain Oct 20–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 65°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
    9Low77°/58°dry
  2. Mon
    12Low80°/55°dry
  3. Tue
    15Low77°/56°dry
  4. Wed
    18Low77°/66°dry
  5. Thu
    19Low80°/67°dry
  6. Fri
    19Low81°/68°dry
  7. Sat
    23Mod.79°/63°0.3 in

Protect tonight

You can probably skip repellent tonight.

  1. If you're near a creek, pond or heavy shade at dusk, a light application on ankles and arms is plenty.
  2. Good night to tip out any containers holding water; what you empty now won't hatch next week.
Which repellent, and how much: DEET vs picaridinBest natural repellents

Why Tucson's mosquitoes do what they do

Tucson is Sonoran Desert with a monsoon: from July into September, afternoon storms fill washes and yards, humidity climbs, and the Culex that carry West Nile appear in numbers. Pima County's Vector Control program traps and tests through the monsoon and reported the season's first West Nile death in 2025; Arizona led the nation in cases in 2026.

  • Monsoon: July–September storms are the breeding water; the index climbs about ten days after each one.
  • Washes and irrigation: the Santa Cruz and Rillito washes and irrigated yards hold water between storms.
  • Aedes aegypti: established in Tucson's neighborhoods; the county tests for dengue.
  • Heat and dryness: outside the monsoon the index stays low, as 10% humidity grounds mosquitoes.

A typical year in Pima County

What the Bite Index typically reads here each month, from Pima County's 30-year climate normals run through the same model as today's number. The month you're in is marked; the season map shows the same long-run picture for every county.

  1. JJanuary: 0
  2. FFebruary: 0
  3. MMarch: 1
  4. AApril: 2
  5. MMay: 11
  6. JJune: 26
  7. JJuly: 56
  8. AAugust: 86
  9. SSeptember: 67
  10. OOctober: 33
  11. NNovember: 7
  12. DDecember: 0

Local surveillance and West Nile virus

The Bite Index measures nuisance biting, not disease. Pima 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. Warmth and water set the size of the population, tonight's weather sets how much of it flies, and the season and local reports adjust the result. Every factor and today's value for it is listed here so you can check the number yourself. Warmth and Water are exactly the climate core of our county-level mosquito season map; the map shows that core on 30-year normals for every county, and “typical for this month” is the same model run on this county's normals, so the comparison is like for like.

WWater

Rain over the egg-to-adult window (0.2 in. between Oct 20 and Oct 30), expressed as a monthly rate on the same wetness curve the season map uses. At summer temperatures eggs become biting adults in about a week, so today's mosquitoes are last week's rain. Cool weather stretches the window; hot dry days shrink it. Irrigation, creeks and pools keep a 35% floor even in a drought.

Role scales
Today 0%

TWarmth

The trailing two-week average temperature on the season map's curve: nothing below 50°F, full speed at 78–88°F, a small penalty in extreme heat. Multiplied with Water, so a cool fortnight caps the index however wet it has been.

Role gates
Today 53%

ATonight

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. Scales the index between half and full.

Role 0.5–1×
Today 66%

GGround truth

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

Role ±15%
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.

Role ×
Today 60%

index = 100 × S × [T × (0.35 + 0.65·W)] × (0.5 + 0.5·A) × (1 + 0.15·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 Tucson

When is mosquito season in Tucson?
Monsoon season, July through September, lingering into October. The rest of the year is too dry for much activity outside irrigated yards.
Why do mosquitoes appear so suddenly in Tucson?
Months of dry weather leave eggs waiting in washes and containers; the first monsoon storms hatch them all at once, and warm temperatures finish the cycle in about a week. The surge follows the first big storm by 7 to 14 days.
Is West Nile virus a risk in Tucson?
Yes. Pima County records West Nile cases most years, including deaths, and Arizona led the nation in 2026. The county's announcements are authoritative; follow them over the index.
Where does this forecast's data come from?
Open-Meteo weather for downtown Tucson, scored by our documented model with desert-specific humidity and heat terms, and compared with Pima County's season-map climatology. Irrigation isn't in the weather data.

Also covers Oro Valley, Marana, Sahuarita, Vail, Catalina Foothills, Green Valley, Sabino Canyon, the Rillito: the forecast point is central Tucson, and conditions within about 30 miles track it closely. Weather fetched Nov 8, 3:28 PM local time.

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