The weather will be anywhere from 62-79 F
The water may be somewhat cold for swimming but remember weather temps are not guaranteed. It could be near 90 by the time you cruise. The Caribbean is like that.
Anyways, here's how to figure it out on your own:
The conversion equation for celsius to fahrenheit is F = (C x (9/5)) + 32.
So, first, multiply degrees celsius by 9. Then divide that number by 5. 17 x 9 = 153. 153/5 = 30.6.
Then, add 32 to that number. 30.6 + 32 = 62.6 degrees fahrenheit.
Read more: http://wiki.answers.com/Q/17_celsius_equals_how_many_degrees_fahrenheit#ixzz1GgIgMi95