You can prepare a template to use with String.Format:
private const WeatherDataTemplateString =
@"Weather Information
GEO Potentail Height (Gpm) : {0}
Pressure (pa) : {1}
Sea Tempreature (K) : {2}
Significant Height of Wind : {3}
waves & swell(m) : {4}
Wind Speed(m/s)/Direction(°) : {5}{6}";
;And, call it like this:
textBox1.Text = string.Format(WeatherDataTemplateString, 1, 2, 3, 4, 5, 6, 7);
Just use your 'WeatherInfo and 'str array data to fill out the item list.