Hurricane Irene is poised to move up the East Coast over the next couple of days, bringing wind, rain, and flooding for much of the Mid Atlantic and Northeast. What looks more likely is that the worst of the impacts will be to the east of Philadelphia, generally along the Delaware and New Jersey coastlines. However, locally we will see some impact from rainfall on saturated ground and the potential for stream and river flooding is possible in parts of the Philadelphia suburbs.
There is some question as to how far west the heavy rain shield ultimately gets -- some computer modeling is hinting that the shield only gets as far west as Pottstown or Reading, with others painting a soggy scenario a bit farther west. Slight nudges east or west with the storm over the next 48 hours will determine where the heavy rain shield sets up. If the current projections hold on this storm, Berks County looks to be the place that will see that cutoff in rain -- generally ranging from one inch on the western side of the county to perhaps as much as six inches on its eastern border. It's a rather sharp cutoff but in tropical systems it's not unusual.
For Montgomery and Chester, rainfall should average between three to six inches in Chester County, four to eight inches in Montgomery assuming the cutoff sets up in Berks. Winds could gust to 50 miles per hour in Montgomery County's eastern edge, to 40 miles per hour in Chester, and 35 miles per hour in Berks. The gusty winds could do enough to cause some localized power outages in spots as they knock trees over from their waterlogged soils.
The storm's timing looks to bring the brunt of the storm in Saturday night through early afternoon Sunday before ending from south to north during the afternoon. Rainfall will start up Saturday across the burbs from southeast to northwest in advance of Irene but the gustiest wind and heavier rainfall will impact on Sunday.