At 5 pm, Irene has weakened to 100 mph. This is weaker than what was forecast yesterday and the storm is now rated a low-end Category 2. The Hurricane Center reports that the storm's inner core has lost its structure, and strong winds are impinging on the storm at upper levels. Thus, the storm is likely experiencing the effects of increased wind shear, cooler water, and perhaps dry air entering along its west side. Any opportunity for re-intensification seems to be dwindling.
However, Irene remains a very large storm, with tropical storm winds extending 250 miles east of center, and a large core of hurricane-force winds. Irene is still a very potent, serious system, and will remain so, for at least the next 48-72 hours. In fact, the Hurricane Center cautions us that whether the storm is rated a weak hurricane, or an intense tropical storm...the hazards will remain the same.
The storm is expected to begin accelerating to the north and northeast tomorrow, which will usher in its effects a few hours sooner for the Baltimore region. The worst weather will come Saturday night, and the effects will begin to diminish Sunday morning. The rains will likely end early Sunday, but the winds may take longer to calm down. In fact, even though the storm will be moving away from the region on Sunday afternoon, some of the faster winds at higher levels may mix down to the surface, creating gusty conditions. These winds mix down because of turbulence, which is caused when the Sun warms the surface and the air begins to percolate.
The first image below is a radar snapshot of the storm from late this afternoon, showing outer spiral rain bands scraping North Carolina (courtesy of Weathertap). The second is a special satellite image, which shows the amount of moisture (water vapor) in the atmosphere (courtesy of Weathertap). Notice the very dry air across the southeast U.S., right up along the west side of Irene. The final image shows the Hurricane Center's 5 pm track prediction (Courtesy of Stormpulse). The storm's position is shown at 2 AM Sunday, when Baltimore's weather deteriorates. The storm is predicted to be a weak Cat 1 at this time (80 mph). The outer white semicircle is the predicted radius of tropical storm force wind. Note that Baltimore is right on the edge.