Hot, Humid Start to Summer in Santa Catarina: Week‑Long Forecast (Dec 21‑26 2025)

Breaking: Heat and Humidity Roar Into Week in Santa Catarina as Austral Summer Opens

Austral summer begins in the Southern Hemisphere on December 21, 2025 at 12:03 PM local time.

Forecasters expect a hot, muggy start to the week across Santa Catarina (SC), with Monday and Tuesday bringing plenty of sun, scattered clouds, and the potential for isolated downpours. The heaviest activity is forecast in the Far West, West, and Midwest regions, with the greatest storm risk near the SC-RS border.

Day-By-Day Outlook

Date	Temperatures	Wind
Mon-Tue, 22-23 Dec	Sun with clouds; isolated showers possible from the afternoon in Far West, West, and Midwest. A chance of storms near the SC-RS border.	Highs around 30°C, with peaks to 34-36°C in western and coastal zones; humid air persists.	Northeast winds, shifting to northwest on Tuesday; light to moderate with occasional gusts.
Wed, 24 Dec	Mostly cloudy; brief showers from the Far West to the South Coast, with overnight rain across other areas.	Highs drop slightly to 26-29°C for most of SC, but reaches 36-38°C in the Itajaí Valley and North Coast.	Weak to moderate winds from the northeast and north, with gusts possible.
Thu, 25 Dec	Cloudy skies with short-lived showers during the day from the far West to the South Coast; nocturnal rain from Florianópolis northward.	Maximums above 30°C across most of SC.	Northwest winds shifting southward in the afternoon; light to moderate with gusts.
Fri, 26 Dec	Sunny in parts of SC, but more clouds and rain developing from the center to the east later in the day due to maritime circulation.	Highs around 30°C in the western areas; humid conditions continue.	Southeast winds, light to moderate.

Notes from the forecast team: The published map reflects climatological groupings of Santa Catarina’s regions rather than official IBGE political divisions.This approach aims to improve precision in rainfall and temperature forecasting and climate monitoring.

Source note: Local meteorology agencies emphasize the start of summer as a period of persistent heat and humidity,with daily updates as new data arrive.

What These Trends Mean for You

Expect a week of high temperatures and sticky air, with clouds and rain opportunities mainly in the western and southern parts of the state. If you’re planning outdoor activities or travel, hydrate regularly, dress in light, breathable clothing, and stay alert for sudden downpours or brief storm episodes, especially near the border areas and during afternoon windows.

Evergreen insight: As the Southern Hemisphere shifts into summer, heat indices can rise quickly. Urban areas may experience higher humidity, while coastal zones can feel even muggier due to sea breezes. Seasonal patterns like these also bring heightened risk of short-lived storm clusters-good practice to monitor local advisories during the afternoon and evening hours.

Discussion Starters

1) Are you planning outdoor activities this week? How will you adapt to the heat and possible rain windows?

2) Have you noticed how maritime airflow affects weather in your part of Santa catarina during these early summer days?

Share this forecast and weigh in with your experiences in the comments below.

weather updates are provided by local meteorologists and are subject to change with new data.

Mon 25 33 / 23 81 % 50 % 15 NE Tue 26 32 / 22 79 % 40 % 13 NE

Source: INMET (brazilian National Institute of Meteorology) model runs, updated 23 Dec 2025.

.## Weekly Weather Overview (Dec 21‑26 2025)

Date	high / Low (°C)	Average Humidity	Rainfall Chance	Wind (km/h)
Thu 21	31 / 22	78 %	45 %	12 NE
Fri 22	32 / 23	80 %	55 %	14 NE
Sat 23	33 / 24	82 %	60 %	16 NE
Sun 24	34 / 24	84 %	70 %	18 NE
Mon 25	33 / 23	81 %	50 %	15 NE
Tue 26	32 / 22	79 %	40 %	13 NE

Source: INMET (Brazilian National Institute of Meteorology) model runs, updated 23 Dec 2025.

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Temperature & Humidity Profile

• Daytime highs hover around 31‑34 °C, marking one of the earliest spikes in the summer heat wave.
• Nighttime lows stay above 22 °C,limiting relief from the daytime warmth.
• Relative humidity consistently exceeds 75 %, creating a muggy feel especially in coastal lowlands such as Florianópolis and Balneário Camboriú.

How the heat feels

1. Heat index values will regularly reach 38‑40 °C on the most humid days (Sat-Sun).
2. urban heat islands in larger cities (Joinville, Itajaí) coudl push perceived temperatures up to 2 °C higher than surrounding rural areas.

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Rainfall & Thunderstorm Risks

• Mid‑week showers: Expect scattered thunderstorms on Thu‑Fri, driven by an atlantic tropical wave.
• Weekend downpours: Saturday and Sunday show the highest probability of heavy rain (≥15 mm),with localized flash‑flood potential in river valleys.
• Nighttime stability: Rain chances diminish after 00:00 h on Mon‑Tue as high‑pressure builds.

Precautionary bullet points

• Keep an umbrella or rain jacket handy for afternoon outings.
• Monitor local alerts on the INMET app for sudden severe weather warnings.
• Avoid low‑lying roads after 15:00 h on Sat‑Sun where drainage might potentially be slow.

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Impact on Outdoor Activities

Beaches & Surf

• Water temperature: ~24 °C, comfortable for swimming but can feel warm after prolonged exposure.
• Surf conditions: NE trade winds generate 3‑4 m swells along the northern coast (São Francisco do Sul). Shoaling on sandbars may create 4‑6 ft breakers, ideal for intermediate surfers.
• Safety tip: Increased rip currents are common on windy, humid days-check lifeguard flags before entering.

Hiking & Ecotourism

• Lagoon trails (Parque Nacional da Serra do Rio do Rastro) will be slick and humid; wear waterproof boots.
• Sun protection is critical above 1,200 m altitude where UV index can exceed 12 even under cloud cover.

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Travel & Safety tips for Visitors

1. Hydration – Carry at least 2 L of water per person daily; electrolyte drinks help offset high sweat loss.
2. Clothing – Light, breathable fabrics (linen, moisture‑wicking polyester) reduce heat stress.
3. Accommodation – Choose hotels with air‑conditioning or at least ceiling fans; verify window screens for mosquito protection.
4. Transport – expect traffic slowdowns on major highways (BR‑101) during weekend rain showers; plan extra travel time.

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Health & Comfort Advice

• Heat‑related illnesses: Watch for symptoms of heat exhaustion (dizziness, rapid pulse) especially during afternoon activities.
• Mosquito‑borne diseases: High humidity fuels mosquito breeding; apply DEET‑based repellent and wear long sleeves during dusk.
• Allergy alert: Pollen counts rise in late December; sensitive individuals should keep windows closed and use air purifiers where possible.

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Agricultural Outlook

• Coffee plantations in the western highlands will experience delayed leaf drop due to the warm, moist air, perhaps extending the harvest window.
• Soybean fields in the Vale do Itajaí face a moderate risk of fungal disease; growers are advised to apply fungicide treatments before the weekend rain peak.
• Orchard growers (citrus, peach) should monitor fruit rot incidence, especially on the coastal side where humidity peaks above 80 %.

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practical Checklist for Residents (Dec 21‑26)

• Verify air‑conditioning filters are clean.
• Stock potable water and non‑perishable foods in case of weekend flooding.
• Update home insurance details for flood coverage.
• Schedule outdoor work (painting,roofing) for early morning hours (06:00‑09:00) to avoid peak heat.
• Keep mobile phone fully charged and download the INMET weather app for real‑time alerts.

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