August 23, 2011: Irene To Become Major Storm, Landfall Likely Over North Carolina, Baltimore May Experience Effects

Irene is moving over very warm waters of the Sargasso Sea with little wind shear to impede continued deepening.  Intensification to Cat 3 or Cat 4 seems more certain.   The prediction models also remain fairly tightly clustered in terms of track, and the model consensus has trended toward an eastward shift in track.  The Hurricane Prediction Center at 11 pm has nudged its official track eastward a bit, with landfall most likely over eastern North Carolina.   The storm center may cross the mouth of the Chesapeake Bay early Sunday.  Given these trends, what is the likely impact on the Baltimore region?

The storm's predicted intensity makes this a particularly dangerous system, even a hundred or more miles from center.   Certainly, the eastward-trending track is a good thing for Baltimore.   But if part of the storm's circulation remains over the warm Gulf Stream, it could maintain hurricane status as it moves by Maryland.   A more intense storm means stronger winds, across the board.   Also, the Maryland impact is still 5 days out.   The track error at 5 days is 250 miles.   That's a huge swath of uncertainty...ranging from the storm passing hundreds of miles to our east, to tracking up the spine of the Appalachians.   But the most likely scenario puts Baltimore in the left semicircle, a fair distance from the center.  Winds are usually 20-30 mph weaker on the left side, are further reduced by surface friction compared to open water, and diminish rapidly as distance increases from the center.  But as these tropical cyclones interact with mid-latitude weather systems and the Appalachians, more often than not the location of heaviest rainfall shifts to the left of track.   So what we miss in terms of wind, we gain in terms of heavy rain. 

If track trends continue eastward, the worst case scenario would involve the storm moving up the western side of the Bay, with the center passing close to Baltimore.  This would potentially generate a powerful storm surge moving up the Bay, and threaten the Tidal Potomac, Baltimore Inner Harbor, and Annapolis...a la Isabel in 2003.   Let's hope this isn't the case.

As for now:  Sunday and Sunday night looks like a rainy, breezy day in Baltimore. 

The image above (from Stormpulse) shows the 11 pm official track and cone of uncertainty, superimposed on a dozen predictions of storm track made by the various models.  When the impact is still 4-5 days out, it's important not to get "hooked" on the solution of any one model...but rather, look for trends that remain consistent from day to day.  That one trend thus far has been to shift the storm's track progressively further and further east.