Istanbul residents and visitors should plan for a wet and potentially disruptive Tuesday night and Wednesday. AKOM's 21 September warning says a cooler, wetter air mass moving in from the Balkans will bring a sharp temperature fall, strengthening northerly winds and periods of heavy, thundery rain across the city.
The message is not that every district will receive the same amount of rain at the same time. The 30–60 kg/m² figure is a forecast range for areas that receive the stronger downpours. But the combination of intense rain, thunder, lightning and strong local bursts is enough for AKOM to warn about sudden flooding and transport disruption.
The short version
Heavier rain: expected after 20:00 Tuesday 22 September.
Warning window: periods of strong rain may continue until around 17:00 Wednesday 23 September.
Possible totals: 30–60 kg/m² in parts of the city.
Wind: northerly winds around 20–50 km/h from Tuesday morning.
Main risks: sudden flooding, lightning and transport disruption.
Before travelling: check the latest AKOM/İBB notice and your transport operator, because forecasts and service conditions can change.
1. When is the rain expected to be strongest?
AKOM says the weather change begins during Tuesday 22 September. Northerly winds are expected to strengthen from about 09:00, generally in the 20–50 km/h range, while temperatures that had been running around 26–28°C are forecast to drop by roughly 6–8°C.
Showers may occur through the day, but the more important period for planning is Tuesday evening. AKOM expects the rain to increase in intensity from around 20:00, with heavy thunderstorms possible overnight and into Wednesday. The agency says strong rain transitions may continue until approximately 17:00 on Wednesday 23 September.
That makes the Tuesday evening commute, late-night movements and Wednesday daytime travel the periods most worth rechecking before setting out. If you have flexibility, avoid building a tight cross-city itinerary around a single connection during the peak forecast window.
2. Where could the heaviest rain fall?
AKOM's citywide warning specifically highlights the European side, the Bosphorus area and the Asian side generally as places where rainfall totals in the stronger cells could reach roughly 30–60 kilograms per square metre.
That figure should not be read as a guaranteed uniform total across Istanbul. Convective storms can be highly uneven: one district can receive a short, intense downpour while another nearby sees much less. The practical point is that localised flooding can develop quickly where a heavy cell stalls over roads, underpasses or low-lying areas.
The atmospheric setup described by AKOM — humid air near the surface with colder air aloft — also supports thunderstorms, lightning and sudden bursts of heavier rain. Residents should treat a dry spell in one neighbourhood as a temporary local condition rather than proof that the warning has ended.
3. What could this mean for transport?
AKOM explicitly lists transport disruption among the risks. Heavy rain can slow road traffic, create water accumulation on lower roads and underpasses, and make transfers between metro, tram, bus and ferry services less predictable. Exposed ferry routes can also be affected by wind and sea conditions even when rail services continue normally.
There was no citywide blanket transport shutdown in AKOM's warning when this article was checked. Do not assume that a service is cancelled — or that it is operating normally — based on the weather headline alone. Check the operator you actually plan to use shortly before departure.
For airport trips, build in additional time for road or transfer delays, especially if travelling during the Tuesday night or Wednesday warning window. If you are taking a ferry, check Şehir Hatları or the relevant operator for route-specific notices rather than relying on a timetable screenshot saved earlier in the week.
4. Practical steps for residents
Clear or avoid blocked drainage points where it is safe to do so. Sudden downpours cause the biggest problems where water cannot drain. Do not enter moving floodwater or attempt to clear a drain in unsafe traffic or water conditions.
Move vulnerable items away from basement or ground-level flood paths. If your building or street has a history of water entry, Tuesday afternoon is the useful preparation window rather than waiting for the heaviest rain to begin.
Charge phones and keep official alerts accessible. AKOM, İBB and transport operators can update conditions quickly. Lightning is part of the official warning, so avoid exposed waterfronts, hilltops and open spaces during active thunderstorms.
Allow more time for the evening journey. Even where metro and rail lines are operating, congestion around stations and slower road feeder services can turn a normal trip into a much longer one.
5. What travellers should change
If Tuesday evening or Wednesday is a sightseeing day, favour plans that are easy to shorten or move indoors. A museum or indoor attraction near a metro stop is easier to manage than a schedule that depends on long walks, multiple ferry crossings and tightly timed outdoor stops.
The Bosphorus is still one of Istanbul's best experiences, but this is not a good forecast window for treating a boat trip as non-negotiable. Check the live service status and be willing to shift it to another day if wind, visibility or operator notices make the outing poor value.
Wear footwear that can handle standing water and slippery paving, protect electronics and passports, and keep accommodation details offline in case mobile data becomes inconvenient during a disrupted journey. Taxis and app cars can become slower and harder to obtain when road demand spikes in bad weather.
If you are arriving or departing through IST or SAW, the most useful precaution is simply extra transfer time. The warning is about conditions across the city, not a prediction that either airport will close.
6. What is forecast — and what is not
This article reports the official AKOM forecast issued on 21 September. It is not a claim that every forecast amount will be observed. Timing, storm tracks and district-level rainfall can change as the system develops.
The official wording forecasts the stronger period from Tuesday evening and continued heavy-rain transitions until Wednesday afternoon. It does not provide a street-by-street schedule, and it does not announce a blanket closure of schools, public transport or attractions in the warning itself.
For a decision that depends on conditions at a specific hour — a flight transfer, ferry crossing, outdoor ticket or long drive — re-check official sources close to departure. Weather news is most useful as a planning trigger, not as a substitute for a live operational notice.
7. Sources and verification
This article was checked on 22 September 2026 against the official AKOM warning issued 21 September. The same timing, rainfall range, wind forecast and risk wording were cross-checked against Anadolu Agency's 21 September report.
Recheck before travel: forecasts evolve. AKOM/İBB and the relevant transport operator are the authority for new warnings, closures or service changes after this article's verification time.
