Hurricane HD [iTunes link].
It's $3.99 right now but how you can put a price on peace of mind? I have to admit, I did get it while it was on sale for $2.99 and when Fernanda started off in the Eastern Pacific.
Now, I am a former weather producer and I know a little something about weather. Although I'm not a meteorologist, I've used the tools they use to bring you latest about the weather and storm tracking.
I am very impressed with Hurricane HD. Once you enter the app, you see right away the current storms by name at the top of the screen. You see a storm track and the areas that might be affected. While this will not replace what a meteorologist uses, this is more than capable for the layperson who just needs to know how the storm is tracking.
A lot of information about storms is available by NOAA at the National Hurricane Center. But that website is made for meteorologists and it's hard to navigate if you don't know your stuff.
I'm pretty sure I haven't yet accessed all of the great features of this app.
If you're looking for an iPad app that will track storms all over the world, this is it.