The average temperature in Hualien as below. It might be lower by 5~10℃ if a cold snap comes in winter. Daytime temperature might be as high as 30~37℃ in summer.
About the rainfall, it usually rains in Hualien all year around. Therefore, we suggest you bring an umbrella (Taroko Gorge Tour) / raincoat (Zhuilu Trail Hiking) with you. Go to link if you would like to check the recent weather.
Typhoon seasons are on July, August, and September and on average, 3~6 Typhoons per year will strike Taiwan during those 3 months.