Was hurricane Irene over-hyped?

On August 20th, 2011 a tropical wave came off the west coast of Africa and formed convection as it moved west towards the Lesser Antilles. The system became well defined and organized thanks to the warm open waters of the Atlantic Ocean. The Hurricane Hunters began to notice circulation at the center of the new formed low pressure system. They sent out a dropsonde device (used to measure storm systems out in open waters and nor’easters) which confirmed their observation that it was becoming Tropical Storm Irene. Unobstructed by neither a frontal system nor a powerful jet stream, Irene never experienced any shearing which allowed the storm to continue west towards the United States and become a hurricane.

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Hurricane Irene became the first hurricane since Hurricane Ike in 2008 to make landfall in the mainland United States. Irene made landfall off the coast of North Carolina in the Outer Banks on August 27th, 2011 as a Category 1 hurricane with winds gusting up to 85 miles per hour. Irene continued in a northeasterly direction making a second landfall in southern New Jersey and a third in the New York City borough of Brooklyn as a tropical storm. Irene lost its strength as it entered into cooler waters and moved inland into New England (Figure 1). Much of the damage was caused by heavy rainfall which washed away vital railroad tracks into New York City and roads that cut off isolated communities in Vermont by flash flooding. The cost of the hurricane is estimated to be around 10 billion dollars and caused 45 fatalities spread amongst several states on the East Coast.

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Five to seven days before the actual landfall, the National Hurricane Center (NHC) predicted a landfall for Irene on the mainland United States. Some of the earliest predictions had Hurricane Irene making landfall over Florida. As each day progressed, the NHC revised their predictions moving the landfall of Irene northwest onto South Carolina on August 22nd. Probably the most accurate track the NHC provided on Thursday August 25th was a landfall just south of the Outer Banks in North Carolina with later landfalls occurring in New Jersey and in New York City. Though accurate, the NHC failed to predict the intensity and the timing of the storm. First, even though Irene experienced warm ocean water greater than 80 °F, Irene was slowly heading northward where the temperature was decreasing. This caused the storm to weaken and make landfall as a Category 1 and not as a Category 3. Second, the NHC predicted on Thursday for Irene to move slowly up the east coast, hitting New York City on Sunday evening, the 28th (Figure 2). However, with Irene moving quicker than expected, the predictions were revised to pass through the New York City area on Sunday morning during high tide, which made a difference of twelve hours. With this new revised data, Mayor Michael Bloomberg was able to make critical decision such as shutting down mass transit and evacuating residents from low lying areas hours before the storm struck.

Click on map to view larger image.

Click on map to view larger image.

In the end, the media did at times over-hype the intensity of the storm and its effects on the United States through the collection of data from the NHC; however, Three Scale’s GeoPDF (Figure 3) shows the overall accuracy of Irene’s forecasted track even with five days before the event. A statement that the media reported on Wednesday was that 65 million people could be affected by Hurricane Irene. This statement was proven true when we at Three Scale factored in the cone of uncertainty for Irene across the East Coast of the United States. Prediction models of the storm track can change over time as the path of the storm changes direction and atmospheric conditions become altered. After analyzing Hurricane Irene and collecting the data, this hurricane season is far from over. With less than ten days away from the Atlantic Hurricane Season’s maximum on September 10th, we are already looking at the Hurricane Katia over the Atlantic Ocean.