Today I made a Yahoo pipe, filtering away those from the feed. Here is the resulting feed, containing only positive tsunami warning statements. Behind the scenes, it's created by the simple YQL statement
select * from rss where url="http://wcatwc.arh.noaa.gov/rss/tsunamirss.xml" and description like "%tsunami <strong>WILL NOT</strong> be%"(there's some newline or similar after "be" in the original feed, and it doesn't seem like YQL does any whitespace normalization, but this matches well enough to filter the stuff).
The resulting feed is my enrapturing contribution to today's supposed end of the world. You may note that the feed is currently (and hopefully still, by the time you read this :-) empty - which is, of course, good news. Enjoy!
On a related hacker's note, it would be really handy to extend Google Reader with a "filter this feed" feature that created these more on the fly, without mucking about for an hour in the Yahoo Pipes interface, and then changed the old subscription to the new feed.