Yes

you do need a jacket based on the weather in Northam WA 6401, Australia 1 second ago

Why? Because it's cool. Pleasantly cool, but cool!

54°F12°C & Partly Cloudy

Wind is 6 mph9 km/h from the Northwest, gusting to 11 mph18 km/h

Date	Low	High	Wind	Day	Night
July 14	37°F3°C	62°F16°C	6 mph10 km/h from Northwest	Partly Cloudy	Drizzle
July 15	40°F5°C	60°F16°C	7 mph11 km/h from South	Drizzle	Clear
July 16	34°F1°C	61°F16°C	3 mph5 km/h from North	Clear	Mostly Clear
July 17	39°F4°C	62°F16°C	8 mph13 km/h from West	Drizzle	Drizzle
July 18	40°F4°C	60°F15°C	5 mph8 km/h from North	Mostly Clear	Clear
July 19	38°F4°C	64°F18°C	15 mph23 km/h from Northwest	Rain	Rain
July 20	44°F6°C	52°F11°C	13 mph22 km/h from Southwest	Drizzle	Drizzle

Low of 40°F5°C, High of 61°F16°C
Wind: 7 mph11 km/h
Precipitation: 47% rain