Brooklyn Tornado, September 16, 2010

Philip Lutzak – September 2010

Intro  Just three years after an EF2 tornado roared through western Brooklyn, NY, another tornado hit the borough, only two miles north of where the 2007 event occurred. Although this one was weaker, rated an EF0 on the Enhanced Fujita Scale, it damaged many homes and businesses, severely disrupting life there yet again. This tornado was caused by a severe thunderstorm embedded in an intense squall line that also produced an  EF1 tornado and a macroburst that killed one person in neighboring Queens, NY. Figure 1 at right shows a still image taken from a video of the thunderstorm over Red Hook, Brooklyn. This is the intensifying thunderstorm that eventually produced the tornado over Brooklyn. About 5 minutes before the tornado reached Park Slope, the lower sky developed the classic green color that many people who have seen a tornado speak about. This is the rain shaft of the thunderstorm - NOT the tornado. The line of grey clouds ahead of the rain shaft is the front of the  thunderstorm outflow. In this brief report we'll look at how the National Weather Service determines where the severe weather occurred and what kind of weather feature caused it. Below in Figures 2 a and b are pictures of the damage in Park Slope, Brooklyn. As a caution, if the information here gets too technical for you, please just go to the last paragraph - it sums up the words Brooklyn and Tornado.

Figure 1. Severe thunderstorm moving into Red Hook, Brooklyn. Note that this is NOT the tornado; the area of green color is the heavy rain shaft. Shortly after this, it produced a tornado over Park Slope Brooklyn. 2010-09-16. Courtesy Januszwelin.

Figure 2a. Car crushed by uprooted tree, Park Slope, Brooklyn. 2010-09-16. Courtesy Chris Scalici.   Figure 2b. Tree snapped at middle of trunk, Park Slope, Brooklyn. 2010-09-16. Courtesy Chris Scalici.

Evidence in the damage  The way the damaged trees and debris fall helps storm investigators from the National Weather Service to determine if it was caused by a tornado or straight-line winds. In Figure 3, each red arrow shows the direction that the debris was blown based on physical examination of the area (see photographs.) Since the debris from the storm was distributed in a circular, counter-clockwise pattern in Park Slope, it provides strong evidence that a tornado passed over the area (graphic example.)

Figure 3. Aerial view of Park Slope, Brooklyn. White arrows show where pictures at right were taken.  Red arrows show the wind direction based on how the debris was blown. It can be seen from these red arrows that winds blew in a counter-clockwise direction, adding proof of a tornado. Courtesy Google Maps and Chris Scalici.

Figure 4a. Satellite image of New York City showing the damage paths of the two tornadoes and microburst. Courtesy Google Maps.

Figure 4b. Map of all damaged tree reports received by NYC's 311 problem line. Courtesy New York Times.

Causes  Damaging downdrafts and microbursts in thunderstorms are often associated with "bow echoes." Figure 5 at right is an illustration of radar echoes showing how a thunderstorm in a squall line can develop into a bow echo. If the thunderstorm's steering winds begin to concentrate at its center/rear, the storm gets stretched forward into a bow shape. The leading edge of this arc can produce very high winds such as a micro- or macroburst. In addition, the northern end of the bow sometimes curves backward and forms a small vortex, called a comma head or comma echo, which in turn may develop into a tornado. Since a similar vortex can also spin up at the bottom of the bow echo, resulting in two vortices on either end of the bow, they are also called "bookend vortices." Radar images from this NYC event (Figure 6 below) closely match the illustration in Figure 5 at right. It appears that a bow echo with a comma head/bookend vortex first started forming just southwest of Park Slope (Figure 6a) around 5:30PM. As these features continued east-northeastward, the comma head developed into the EF0 tornado in Park Slope. As this tornado dissipated the bow echo continued to strengthen rapidly (Figure 6b), producing the 125 mph macroburst at 5:40PM over eastern Brooklyn and central Queens and the EF1 tornado at 5:44PM over north central Queens (Figure 6c.) Examining the location and times between the Brooklyn and Queens tornadoes, it seems quite possible that both were produced by the same bookend vortex at the northern end of the bow echo. Here's an excellent, more detailed explanation of bow echo dynamics.

Figure 5. Illustration of radar returns showing the evolution of a thunderstorm into a classic bow echo. Courtesy UCAR COMET.

Figure 6a. Reflectivity radar image 2010-09-16 2135 (5:35 PM EDT). Courtesy Mark Thornton. Original image.	Figure 6b. Reflectivity radar image 2010-09-16 2140 (5:40 PM EDT). Courtesy Mark Thornton. Original image.	Figure 6c. Reflectivity radar image 2010-09-16 2144 (5:44 PM EDT). Courtesy Mark Thornton. Original image.

   This short examination of the severe weather event of September 16th in New York City, with a concentration on the tornado in Brooklyn, is intended to provide some initial assessment of the damage that was caused and the meteorological reasons for why it occurred. A lot more investigation needs to be done.

The Last Word  This short video of the tornado in Brooklyn was taken by two young Brooklynites in eastern Brooklyn near the Queens border. I consider it very important in that it looks like they not only experienced the end of the first tornado but also the fury of the developing macroburst. Watch when they say that "it's funneling" and then it's followed by even higher winds. It certainly looks like they experienced most if not all of the macroburst which eventually reached 125 mph. In addition it is also very entertaining, but be warned: they did some things you are not supposed to do during a tornado warning, and they use very intense "Brooklyn" language (in California accents (!) of all things.) But the intense winds at the end make this well worth watching, and at least they ran when the tree started to disintegrate.