While the city may have escaped Hurricane Irene's wrath that's not true for the Catskills and other places upstate, Western Massachusetts and Vermont where ten inches or more of rain caused devastating floods. Cool, dry weather is moving in behind the storm. This morning's low in Central Park was 59 degrees. That's the first time we've been below 60 since June 15th! We'll see a high in the upper 70s today with lots of flood problems north and west of the city. Tomorrow and Wednesday are expected to be warmer, with highs in the low 80s Tuesday and mid 80s on Wednesday.
The dry air is what quickly weakened hurricane Irene. Hurricanes get a lot of their fuel from the energy that's released when water vapor condenses into cloud droplets. Irene really hugged the East Coast and the storm was large enough that the slightly more westward than expected track allowed it to suck in dry air, which you can see happen to the bottom of the storm as it passes the Delmarva peninsula in the NOAA video below:
Now, you may have read lots of comments here and elsewhere where someone said they read the National Hurricane Center forecast discussions and knew with great certainty that Irene was going to be a bust. We read those discussions too! Here's the money quote from 5 a.m. Saturday: "Land interaction... dry air entrainment.. and increasing vertical wind shear should cause Irene to weaken as it moves along the U.S. East Coast." Sounds like the death knell for Irene doesn't it? But, wait, what's the very next sentence? "However... The cyclone is expected to remain a hurricane with a very large wind field until after landfall in New England." Interesting! Why didn't the people who were so certain Irene was going to wimp out not mention that sentence?
Let's look at the 11 a.m. discussion: "Irene is forecast to gradually weaken as it moves along the East Coast... It could be slightly weaker than predicted." Wow, that Irene is practically harmless, unless you read what follows: "Whether Irene is a strong tropical storm or hurricane over New England will make little difference in the expected impacts of of damaging winds... a dangerous storm surge... and flooding rains." The 5 p.m. discussion says "the radar presentation of the inner core actually improved for a few hours... warrants a return to two-hourly intermediate advisories." On to 11 p.m. "Only slow weakening is expected throughout the forecast period... and it will only take modest convection to bring down stronger winds aloft to the surface as sustained hurricane-force winds." Finally, 5 a.m. Sunday, the last advisory before Irene made landfall "Despite the gradual weakening of the cyclone... the outer wind field continues to expand... Irene is expected to remain near hurricane strength until it moves into southern New England later today." Who are you going to trust, the person full of certitude who cherry picks one data point and gets lucky, or the forecaster who is occasionally wrong but acknowledges the uncertainties of forecasting and includes all available information in their prediction?