While tropical storms such as Karen may be a nuisance in nearly every other respect, they do offer opportunities for seeing unusual bird species inland in Louisiana. The regularity with which land falling tropical cyclones deposit coastal birds- or even tropical seabirds- inland after landfall is predictable enough that birds are now found after virtually every storm. Indeed, some of the most feverish birding behavior can take place immediately after storms pass.
The general strategy of most birders is to stay at home (as often advised by authorities) during the storm's passage, making frequent trips outside to scan the sky during breaks in the rain. Many a birder has added unusual birds to their "yard list" this way.
After things settle down and any official prohibitions are lifted, most birders then scan large bodies of water to look for seabirds, which can be either sitting on shore (or on the water), or flying - often purposefully heading back in the direction of the Gulf. Lake Pontchartrain is usually targeted by birders in our area under these circumstances. Birds will also often sit on wet lawns, such as those in City Park, or the fields across the street from Armstrong Airport (etc.). There is also some indication that birds will continue to come down the Mississippi River for days after a storm passage, if the storm has crossed the Mississippi well upstream from us. This was likely the reason for a jaeger (apparently Pomarine) I saw on the River near the Luling Bridge days after Isaac last year. But generally, the best birding is immediately after the storm passes.
The storm waifs most often reported in the New Orleans area are pretty consistently Magnificent Frigatebirds and Black Terns. Brown Pelicans, Royal Terns, and Black Skimmers may be boosted in numbers. Bridled and Sooty Terns are the most likely truly pelagic species to occur, either over large water bodies or flying steadily overland. Jaegers often turn up as well, especially Pomarine. Many other species are possible, and records in or near Louisiana have been as odd as American Flamingo (after Isaac, last year).
Birds that migrate over us but normally do not pause before reaching the Gulf can sometimes be put down in conspicuous numbers- especially shorebirds. This is also probably the mechanism behind the appearance of a Sabine's Gull I found near the Lakefront Airport during Hurricane Opal (which passed to our east) in 1995. It was accompanied by several Franklin's Gulls, less rare but also hard to come by here under normal circumstances.
Although waterbirds are the main attraction, odd songbirds sometimes turn up. I have seen Gray Kingbird after tropical weather at UNO, and 1984's Hurricane Juan (before I came here) produced a remarkable list of late records of species that should have been in Latin America at the time. Nobody is quite sure how the storm managed to produce this effect.
Unfortunately for us with Karen, the left side of the storm is usually not as good as the east side. But some pelagics can get blown left of the track- as did some Sooty Terns when TS Lee came inland in Louisiana in 2011. These may (?) be birds that were wrapped around in front of the advancing storm by the counterclockwise wind circulation, carrying them all the way around to the left side before the center of the storm passed.
Two main mechanisms are presumed to be involved in storm displacement:
1) birds becoming "caught" in the eye by retreating continuously from the advancing eyewall, sometimes to the point that they will even travel within it miles overland to avoid settling and enduring the eyewall winds.
2) birds are drifted by the counterclockwise circulation, sometimes far inland
Karen has no eye, so the second mechanism should apply.
Tropical cyclones have caused some remarkable displacements. In 2008, a Cory's Shearwater was reported in Oklahoma after Gustav. Several Black-capped Petrels have occurred well inland in the northeastern USA.
Because most tropical weather hits us earlier in the season, Karen's potential for producing waifs may not fit the patterns typical of earlier season storms- it will be interesting to see.
Be safe, and good birding!