Postojna Weather in September

September in Postojna brings pleasant temperatures, with highs of 21°C (70°F) and nights dropping to 11°C (52°F). It's the rainiest month of the year, so come prepared with waterproof gear.

Rainfall in Postojna in September

Postojna is in the rainy season in September, with rain on around 13 days and an average of 181 mm (7.1 in). Rainfall this month is frequent and tends to be fairly heavy when it does fall. Packing waterproofs is a good idea.

Temperature in Postojna in September

If you're visiting Postojna in September, expect highs of 21°C (70°F) and overnight lows around 11°C (52°F). Even when the weather is stable, mornings and evenings can still feel distinctly cool. At 11°C (52°F) overnight, it can feel quite a bit cooler after dark. Worth packing something warmer for evenings, but the cooler temperatures are ideal for sleeping.

Sunshine in Postojna in September

Enjoy a sunny month with about 211 hours of sunshine, even though this month falls in the wet season. There is still enough sun to enjoy the outdoors.

If you prefer dry days with pleasant temperatures, May, June, July and August typically offer the best circumstances. If you're seeking pleasant, dry and sunny weather somewhere else in the world, our weather planner can help you explore other options.

Select a Month

Check the conditions for any month of the year.

For a detailed overview over the year and the best time to visit Slovenia, check out our Postojna's climate page.

Postojna Temperature in September

Min Temperature 11°C (52°F)

Max Temperature 21°C (70°F)

Chance of Rain 43%

Precipitation 181 mm (7.1 in)

Rainy days 13 days

Humidity 67% *

Sunshine 211 hours *

Percentage Sunshine 54% *

* Data from: Triest, Italy (38 KM, 23 Miles).

Daily Historical Temperatures

50-year average (1976-2025)

Based on our historical records, temperatures in Postojna typically drop from around 25°C (77°F) at the start of September to approximately 21°C (70°F) by the end. Nights are cool, with lows typically ranging from 10°C (50°F) to 14°C (57°F).

Average temperatures in September

Daily Historical Precipitation

50-year average (1976-2025)

Average daily rainfall for each day of the month based on long-term records.

Average precipitation in September

Historical weather for Postojna in September

Browse day-by-day weather records for Postojna spanning 51 years. Select any month and year to see actual temperatures, rainfall, and conditions recorded on each day.

Postojna historical weather extremes in September

Based on 49 years of weather observations in Postojna between 1976 and 2025, these are the recorded extremes.

Postojna recorded its highest September temperature of 34°C (93°F) on September 23, 1985.
On September 27, 2020, Postojna saw its coldest September day with temperatures maxing out at 10°C (50°F).
Nighttime temperatures dropped to 0°C (32°F) on September 23, 2022, marking the coldest September night on record.

Best Places in Slovenia in September

Find out more about the weather in Slovenia and which places have the best travel conditions in this month. See all of Slovenia in September →

Weather conditions Weather

Temperatures

Precipitation

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Legend

perfect weather

pleasant

tolerable

unpleasant

poor

Perfect weather is subjective. On this map perfect weather has been defined with temperatures between 20°C (68°F) and 29°C (84°F) and not too much precipitation (less than 90 mm (3.5 in) a month).

What to Wear in Postojna in September

For Postojna in September, you'll want flexible clothing. It's wise to pack cotton shirts, comfortable shorts, and a pair of jeans for cooler evenings. A light sweater or jacket is useful for air-conditioned spaces (like buses) or unexpected cool moments. Also bring a poncho, it will rain a lot! Waterproof everything you can. Don't forget sun protection, sunglasses, sunscreen, and a hat. These are all good ideas with this much sunshine.

What To Do in Postojna in September

We rated the following activities from 1 (least suitable) to 10 (best) to do.

Swimming

7/10

Camping

6/10

Select a Month

Check the conditions for any month of the year.

For a detailed overview over the year and the best time to visit Slovenia, check out our Postojna's climate page.