Yes

you do need a jacket based on the weather in Istanbul, Turkey 1 second ago

Why? Because it's cool. Pleasantly cool, but cool.
55°F13°C & Partly Cloudy

Wind is 9 mph15 km/h from the NE, gusting to 22 mph36 km/h
May 5
12am55°F13°C10 mph16 km/h NEPartly Cloudy
1am56°F13°C12 mph20 km/h NEPartly Cloudy
2am58°F14°C14 mph23 km/h NEMostly Clear
3am60°F16°C14 mph23 km/h NEMostly Clear
4am61°F16°C14 mph23 km/h NEMostly Clear
5am63°F17°C14 mph23 km/h NEClear
6am64°F18°C15 mph24 km/h NEClear
7am64°F18°C15 mph25 km/h NEWindy
8am63°F17°C15 mph24 km/h NEWindy
9am63°F17°C14 mph23 km/h NEClear
10am62°F17°C14 mph22 km/h NEClear
11am60°F16°C12 mph20 km/h NEClear
DateLowHighWindDayNight
May 452°F11°C64°F18°C14 mph22 km/h from NEClearClear
May 548°F9°C66°F19°C3 mph5 km/h from EClearClear
May 650°F10°C69°F20°C5 mph8 km/h from SWClearMostly Clear
May 757°F14°C74°F24°C5 mph7 km/h from SWPartly CloudyMostly Cloudy
May 857°F14°C67°F19°C11 mph18 km/h from NECloudyMostly Cloudy
May 956°F13°C65°F18°C14 mph22 km/h from NEMostly CloudyRain
May 1054°F12°C65°F18°C11 mph17 km/h from NMostly CloudyPartly Cloudy

Yes

Low of 47°F9°C, High of 66°F19°C
Wind: 3 mph5 km/h
Precipitation: None

Support This Page