Tropical Storm Karen is due to hit the U.S. Gulf Coast sometime this weekend. While the official forecast map from the National Hurricane Center shows it brushing the eastern tip of Lousiana before taking a right turn that would bring it over the eye over Fort Walton Beach, there are a lot of uncertainties about this storm that make it worth watching and preparing for.
First off, the chart of the various computer models shows that the NHC forecasters are working with some very conflicting projections from some of their most reliable computer models. Forcaster Jack Beven says in his Friday morning discussion that the timing of the right turn Karen is expected to take is very much up for grabs. "The UKMET...navgem...and Canadian models delay the turn until after Karen makes landfall in southern Louisiana. The GFS shows the sharpest turn...and it calls for the center to make landfall on the northwestern Florida Peninsula. The GFDL...HWRF...and ECMWF are between these extremes with landfall forecasts from the mouth of the Mississippi River to the western Florida Panhandle." Beven adds that the confidence level in the forecast track is "low".
Where Karen makes landfall could be even more important than usual, since a combination of wind shear and dry air have created a lop-sided storm with the bulk of the worst weather on the eastern side of the eye. A landfall, at Mobile could put the panhandle's Emerald Coast in line for the worst of the high winds and storm surge. Even if Karen remains a tropical storm sustained winds of 60 miles an hour and heavy rainfall from a slow-moving storm could combine with storm surge to make dangerous flooding possible.
Even more uncertain is the intensity projection. While Karen has been fighting wind shear and dry air, there is plenty of warm water to potentially fuel rapid strengthening. As it stands now, the forecast calls for Karen to be near hurricane strength just before it comes ashore.
This is one of the situations that forecasters and emergency managers dread: a storm that has equal potential to turn into a non-event that leaves residents of areas that go untouched grumbling about everyone "crying wolf", or into a dangerous storm that strengthens rapidly and unexpectedly while taking a last-minute turn.
Bottom line, Karen is not a storm to treat lightly. A slow-moving tropical storm can generate enough rain, wind and storm surge to be a major weather event, even if it doesn't approach the catastrophic potential of a Katrina or Ivan.