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A rain gauge at the Meteorology Laboratory of Bogazici University's Kandilli Observatory and Earthquake Research Institute recorded 129.6 millimeters of rainfall in Istanbul on 15 October, the third-highest daily total in records dating from 1911 to 2026, according to an institute statement.

The same downpour accounted for roughly 74 percent of all rain measured in the city during the first half of October 2026, while forecasters warned that further heavy rain and flooding risk lie ahead in several regions.

Where the 15 October Total Ranks

The institute said the highest daily rainfall ever measured at the station was 165.8 millimeters on 20 July 1951, followed by 131.3 millimeters on 3 October 1942. The 15 October figure places third in the full archive.

When only October observations are considered, the 129.6 millimeters measured on 15 October was the third-highest daily rainfall in the historical record for that month.

Half-Month Totals and Archive Context

Across 1-15 October 2026, Istanbul received a total of 174.3 millimeters of rain. That amount ranks sixth among historical data for the same 15-day window, and about 74 percent of the period's total fell on 15 October alone.

The Kandilli Meteorology Laboratory's observation archive, which stretches back to 1911, contains 13 separate dates on which daily rainfall reached or exceeded 100 millimeters.

Storm Winds to Ease, Rain to Continue

The laboratory's forecast calls for the heavy rain and storm-force winds affecting Istanbul to weaken from this evening onward, with precipitation continuing for a time at moderate intensity.

The rain-bearing system is expected to move east, bringing heavy rainfall to Kocaeli, Sakarya, Duzce and Bolu, as well as Zonguldak, Bartin and Karabuk in the western Black Sea region. Rain is forecast to persist the following day across Marmara, the Black Sea, northern Central Anatolia and the country's southern and eastern parts, intensifying after midday around Kirklareli and Istanbul's Catalca district.

Weekend Downpours and Flood Risk

Wet weather is expected to persist on Saturday, 17 October, across Marmara, the Aegean, the Mediterranean and Central Anatolia. Forecasters flagged a risk of heavy rain, floods and inundation in the inland Aegean after midday and in Istanbul, eastern Marmara and the western Black Sea during the evening and night hours.

Rainfall expected in the western Black Sea on Saturday night could be stronger than what was measured on 15 October. Precipitation is forecast to weaken generally on Sunday, 18 October, before returning at lower intensity on Monday and Tuesday along Istanbul's northern coasts and in the western Black Sea.

Key Takeaways

• Istanbul recorded 129.6 millimeters of rain on 15 October, the third-highest daily total in records from 1911 to 2026
• The record daily high at the station is 165.8 millimeters, set on 20 July 1951; 131.3 millimeters on 3 October 1942 ranks second
• The 1-15 October 2026 total of 174.3 millimeters ranks sixth for that period, with about 74 percent falling on 15 October
• Forecasters warn of heavy rain and flood risk across several regions through Saturday, with possible stronger rain in the western Black Sea