You're correct in thinking that the present perfect tense (has lashed, have been, etc.) refers to an action that starts in the past and continues into the present. In many cases, there's no reason why you couldn't use either present perfect or present tense--they just mean slightly different things. If you say "the tomatoes are contaminated," your emphasis is on the tomatoes' current state; if you say "the tomatoes have been contaminated," you are subtly highlighting the fact that the action of contaminating the tomatoes started at some point in the past. Either one could be correct.

"Has been lashing" doesn't make quite as much sense. This is present perfect progressive tense (ouch, sorry for the jargon), which should only be used when you really want to emphasize the fact that the action continues to take place. In this case, it seems that "lashed" (or possibly "has lashed" if the storm is still on the rampage) would make more sense, since the couple (apparently) already canceled the wedding at some point in the past.

Practically speaking on the GMAT, you rarely need to worry about whether present perfect tense would be a better choice than simple present tense. The important thing is to recognize that different verb tenses should be used for two different actions in the same sentence ONLY if the actions occurred at different times. Check out SC #87 in the 12th edition of the official guide for a good example of when to use present perfect and simple present tenses to describe actions that occurred at different times.

I hope this helps!