David: I'm not sure that there is any forward weather app that is any good for the VI. Since there will always be some clouds, and it is likely to rain somewhere, sometime, for a few minutes on any given day, they play it safe and show clouds and "showers" nearly every day. Chances are that you will have great weather this time of year. The only typical lengthy overcast or rainy times are a week or so sometime in April-May, and again in November. We are headed down shortly, and expect great weather, warm water, and no crowds.
"What's past is prologue". You can get a better sense of upcoming weather by checking out the current and past weather, and extrapolating from there. First, at this time of year, rule out any dramatic weather surprises by checking here:
http://www.nhc.noaa.gov
That yellow "X" off the coast of Africa would take at least eight days to arrive, but is much more likely to fall apart, or steer well north of the VI into the open Atlantic.
Then, check a large scale weather loop; this one captures the entire Atlantic ocean, over the past 24 hours:
http://images.intellicast.com/WxImages/ ... e_anim.gif
For a closer look over the last ten hours, click here:
http://wwwghcc.msfc.nasa.gov/cgi-bin/ge ... mframes=20
And for a view zoomed in on the VI, over the last five hours, with details on how to interpret the images, go here:
http://www.vi-satweather.com
Enjoy your visit!
All the best,
Kevin