*The role of the weather on 9/11...twenty-five years ago*
Paul Dorian
The NOAA weather map at 8 AM, September 11, 2001.Map courtesy NOAA, AccuWeather
Overview
It is hard to believe that it was 25 years ago...a day that will never be forgotten...and the weather featured exceptionally clear, calm and sunny conditions across the Northeast US. A strong cold frontal system had pushed through the northeastern states on the previous night producing strong thunderstorms and paving the way for a spectacular weather day on Tuesday, September 11th, 2001. The 11th of September happens to fall right around the climatological peak of the Atlantic Basin tropical season and indeed there was a hurricane, Erin, that sat just 500 miles off the coast of New York City and its wind circulation helped to play a role in the aftermath of events that unfolded on that day.
A high-pressure system was in control of the weather in New York City on September 11, 2001, as Hurricane Erin loomed off the coast to the east. This satellite image shows both the hurricane and the smoke rising from Ground Zero where the Twin Towers once stood. The prevailing wind between the two systems was north to south, which caused the southward drift of the smoke. (Courtesy NASA / AccuWeather)
Details
A strong cold front pushed through the northeastern states on the night of September 10th (Monday) producing strong thunderstorms along its path. In fact, the World Trade Center was struck by lightning as many as 6 times on the evening of September 10th by multiple thunderstorm cells. The passage of the cold front was paramount on how things played out on the following day as it paved the way for strong high pressure to build into the northeastern states from the Upper Midwest. The high-pressure system resulted in wall-to-wall sunshine across the Northeast US on Tuesday, September 11th and importantly, produced light winds and unlimited visibility – ideal flying conditions.
Like many tropical systems in 2001, Hurricane Erin stayed out over the Atlantic Ocean and never reached the US east coast. Hurricane Erin peaked as a category 3 (major) storm on September 9th and sat about 500 miles to the east of New York City on 9/11. Map courtesy NOAA, Wikipedia
The incoming high-pressure system was part of the overall weather pattern which had an influence on Hurricane Erin and kept it away from the coast by some 500 miles or so on 9/11. The climatological peak of the Atlantic Basin tropical season is right around that stage of September and while it was a fairly active season, most systems stayed out over the Atlantic Ocean in 2001.
From a climatological point of view, the peak of the Atlantic Basin tropical season comes right around the 10th of September when sea surface temperatures are near their peak in much of the Atlantic Ocean’s Main Development Region. Plot courtesy NOAA
Erin was the first tropical system in 2001 that reached hurricane strength peaking as a category 3 (major), and it ended up having the longest life span of any hurricane that season. The combination of the incoming high-pressure system and Hurricane Erin spinning off the coast resulted in a northerly wind in the New York City metro area and this resulted in a southward movement of the smoke that emanated from the Twin Towers, pushing the plumes toward Brooklyn and the Jersey Shore rather than across the Hudson River.
While 2001 was a fairly active tropical season in the Atlantic Basin with 15 named tropical storms and 9 hurricanes, the majority of the activity stayed out over the Atlantic Ocean including Hurricane Erin in September. Map courtesy Plymouth State University Weather Center, NOAA
The weather was indeed quite important on how events unfolded on 9/11, and one wonders how things would have turned out if the cold frontal passage was a day later or if Hurricane Erin had come closer to the east coast or if low hanging clouds were obscuring the tops of the World Trade Center towers. It is certainly a day that you wish didn’t have such perfect weather conditions in the Northeast US.
Meteorologist Paul Dorian
Arcfield
arcfieldweather.com