August 22: Irene Predicted To Become A Major Hurricane

The Tropical Prediction Center forecasts Irene to move up the Eastern Seaboard east of Florida and intensify to a Category 3 (Strong) hurricane.   The latest landfall guidance at 5 pm today brings the storm inland along the NC/SC border 2 pm this Saturday. 

It's still too early to discern the potential impacts on Baltimore.  When post-tropical remnants come inland, and combine with pre-existing weather systems in the Mid Atlantic, we call this process extratropical transition (ET).  How ET plays out in terms of who gets what type of severe
weather (flash flood, river flooding, high winds, tornadoes, damaging surf) depends on myriad factors,
including:  (1) storm intensity; (2) storm size;  (3) storm speed;  (4) storm track;  (5) interaction with the Appalachians; and (6) interaction with weather systems such as fronts, areas of low pressure and jet stream features.   Every post-landfall scenario is unique, and many are poorly forecast.   Just look at the different outcomes for Hazel (1954 - damaging wind storm), Camille (1969 - 27" rain in 8 hours in the Blue Ridge), Agnes (1972 - widespread river flood in the Susquehanna Basin), Isabel (2003 - widespread wind damage and storm surge in the northern Chesapeake Bay), Gaston (2004 - localized flash flood killing 13 in Richmond) and Ivan (2004 - tornado outbreak across Northern Virginia).

But I am becoming increasingly confident that Baltimore will experience periods of heavy rain and gusty winds for some portion of this weekend.