Hurricane warnings and mandatory evacuations have been posted for coastal New Jersey in advance of Hurricane Irene. A hurricane watch is in effect for New York City and surrounding counties. Irene has started to weaken somewhat and will continue to do so after it hits the Jersey shore. But it will be a potent storm capable of causing widespread damage when it hits the city. Do not underestimate the power of this storm and its ability to cause harm.

Of greatest concern is the height and timing of the storm surge. Air circulates counterclockwise around hurricanes. This raises the level of the sea on the northeastern corner of the storm. As Irene approaches that storm surge will smack into Staten Island, the beaches of Brooklyn and Queens and lower Manhattan. The timing of the storm is such that the surge may strike at high tide tomorrow evening. It is too soon to tell how high the storm surge will be but the potential exists for major beach erosion and flooding.

Hurricane Irene path from the Weather Underground

The area of tropical storm strength winds surrounding Irene is several hundred miles in diameter. The city will be subject to many hours of steady 40-60 mph winds as the storm comes ashore. The wind is expected to pick up late tomorrow afternoon or early in the evening. Steady 60-70 mph winds, with higher gusts, are possible on Sunday morning.

Thanks to yesterday's showers August has now had over a foot of rain. Another 6-10 inches could be added to that total this weekend. The ground is already saturated. That rain has nowhere to go, so significant and widespread flooding is expected across the city. Trees with their roots in balls of mud instead of dry ground will be toppling under the high winds.

Once Irene moves just slightly north of the city it will get picked up by the westerlies and be quickly swept toward the Canadian Maritimes. The winds will diminish to less dangerous levels by late Sunday afternoon and the rain should end early Monday morning. The weather behind the storm should be very pleasant.