Headed into the Fall of 2001, climate models and forecasts indicated the possibility of an impactful tropical season. As with any tropical season, the best we could do is hope the season wouldn't host devastation, and fortunately for the Eastern united states, this wish was granted... if in no other way, meteorologically speaking. On September 1, 2001, a wave coming off the coast of Africa formed into a Tropical Storm Erin, the 5th named cyclone of the Atlantic season. Models had it moving east, at points concerningly close to the US East Coast.
As it continued to develop and push east, it veered sharply North and West towards Bermuda and the general direction of the NE United States, briefly stirring concerns of a landfall in the east coast region. Fortunately for CONUS, models had this intensifying Hurricane getting caught in a mid-level trough from the Canadian basin by the time it was nearest to land - nevertheless, with bated breath, meteorologists watched Hurricane Erin meander off of the coast of New England through its closest approach September 10th and September 11th of 2001.
Used primarily to monitor the atmosphere, the GOES-8 satellite was keeping a close eye on Erin - as it began to be impacted synoptically by the aforementioned mid-level trough that was beginning to pull it northeast, much of the East Coast was in it's leftmost wind regime, with winds lightly out of the north to slightly northwest, and clear conditions abound as it swept dry air in from that direction. Through the morning, a plume of smoke from Manhattan drifting slowly south became visible in this area under Erin's broader influence - the attacks on the morning of September 11th were underway during Erin's closest approach.
It's pure speculation to suggest that the unfortunate that day would have been different had Erin taken a different path - if it had instead approached closer to land, would those flights perhaps have been cancelled? If it happened days later, would search and rescue operations be impeded? Nobody can know for sure. Either way the pendulum was to swing, weather was a consideration in the days following this tragedy, and is often a less-appreciated factor in optimizing plans in such horrific events. It goes without saying that Erin fell to the wayside in the news in the following days, and it eventually dissipated near Greenland a week later, fading back into the jet stream as just another impulse, being lost to history as a close call that could have been much, much worse if not for a conveniently placed trough.