Yes

you do need a jacket based on the weather in Portsmouth, UK 1 second ago

Why? Because sorry, it's too cool for just a hoodie!
58°F14°C & Partly Cloudy

Wind is 5 mph8 km/h from the East, gusting to 10 mph16 km/h
September 26
2pm57°F14°C5 mph9 km/h EastMostly Clear
3pm56°F13°C6 mph9 km/h EastMostly Clear
4pm54°F12°C6 mph9 km/h EastMostly Clear
5pm53°F12°C5 mph8 km/h EastPartly Cloudy
6pm52°F11°C5 mph8 km/h EastPartly Cloudy
7pm52°F11°C5 mph8 km/h EastPartly Cloudy
8pm52°F11°C5 mph8 km/h EastMostly Cloudy
9pm52°F11°C5 mph8 km/h EastMostly Cloudy
10pm53°F11°C5 mph9 km/h EastMostly Cloudy
11pm53°F12°C5 mph8 km/h SoutheastMostly Cloudy
September 27
12am53°F12°C5 mph8 km/h SoutheastCloudy
1am53°F12°C4 mph7 km/h SoutheastCloudy
DateLowHighWindDayNight
September 2548°F9°C59°F15°C5 mph7 km/h from EastMostly CloudyPartly Cloudy
September 2652°F11°C61°F16°C10 mph16 km/h from SouthCloudyMostly Cloudy
September 2752°F11°C64°F18°C6 mph10 km/h from WestMostly CloudyMostly Clear
September 2848°F9°C63°F17°C4 mph6 km/h from WestPartly CloudyPartly Cloudy
September 2949°F9°C64°F18°C4 mph7 km/h from WestPartly CloudyMostly Cloudy
September 3052°F11°C64°F18°C4 mph7 km/h from SoutheastPartly CloudyPartly Cloudy
October 153°F12°C64°F18°C5 mph9 km/h from SoutheastMostly CloudyMostly Cloudy

Yes

Low of 52°F11°C, High of 61°F16°C
Wind: 10 mph16 km/h
Precipitation: 22% rain

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