There is a rumor going around that Irene is weakening and that perhaps the hurricane won’t be all that bad for the Philadelphia and New York City metropolitan areas. This morning I want to put that rumor to bed.
First, I want to be clear that tropical low pressure systems, especially strong hurricanes, can be very unpredictable at times, especially in terms of strength. Because tropical low pressure systems are very sensitive to even the smallest mesoscale influence like a small amount of dry air, hurricanes can weaken unexpectedly. On the other hand, hurricanes also can intensify and in a very short period of time from a category 2 hurricane, which Irene is now at 110 mph winds, to a category 3 (115 mph winds) or higher. Irene is moving into a very favorable environment for intensification and one very significant influence that would support strengthening is that Irene is moving towards the Gulf Stream, which is a very warm body of water, typically in the mid 80’s to lower 90’s in a few spots. This is the body of water Irene will be moving over for the next 12 to 24 hours and that is why one should not let there guard down. So let’s get to the forecast.
High pressure will be in control for today through tomorrow morning with scattered clouds, light winds, and comfortable weather conditions. Temperatures will be near normal in the lower to mid 80’s along the immediate coast and mid to upper 80’s elsewhere. Overall a very pleasant late August day can be expected throughout the northern Mid Atlantic.
As hurricane Irene moves north tomorrow evening, the outer bands of Irene will start to move into southern New Jersey and then drive northward through the entire northern Mid Atlantic. These bands of rain will be heavy at times and will increase in intensity through tomorrow night and into Sunday morning.
The worst hurricane conditions are expected Sunday morning through Sunday evening for the entire northern Mid Atlantic.
Along the coast will be the worst conditions with sustained winds of 75 to 100 mph with higher gusts, significant coastal flooding with a storm surge potential of 2 to 10 feet depending on the timing of high/low tide per location, intensity of Irene as Irene moves along the coast, and orientation and size of certain bays and coast lines. Heavy rainfall will produce rainfall amounts over 6 inches and possibly as much as a foot of rain leading to significant flash flooding.
A way from the coast, conditions will still be dangerous with a variety of impacts. Rainfall amounts will range from 4 to 8 inches with sustained winds of 45 mph to 75 mph expected. Significant flash flooding and wind damage will be possible as a result of this hurricane.
The entire northern Mid Atlantic is at risk for significant flash flooding and wind damage from this hurricane. One additional factor that is possible is an isolated weak tornado within the bands of rain, which can happen when tropical low pressure systems interact with the coast line.
Weather conditions will rapidly improve by Monday morning with high pressure in control through the middle of next week. Tranquil weather conditions with temperatures near normal and low humidity can be expected.