Former Hurricane Sandy has now moved ashore, with impacts ranging from flooding in parts of the mid-Atlantic and Northeast Regions, to heavy snow and blizzard conditions in the central and southern Appalachians, while wind and other damage to infrastructure has caused power outages to an estimated 7.5 million people. Partially fueling this storm was very warm water in association with the Gulf Stream just off the eastern U.S. shore, with water temperatures estimated at some 0.5 C to 1.5 C (~1-3 F) above normal for this time of year, as shown in the images below from the Climate Prediction Center / NCEP.
I decided to plot the storm’s track across the SPoRT blended SST product to see how this storm tracked across the region of highest SSTs. Since the SPoRT SST product updates every 12 hours with the most recent available data, I created a loop of the SSTs, updating with the 06Z and 18Z product times (click on the image twice to get to the looping page…it may take a minute to load). The SSTs update as the storm track points are plotted on the map. The storm track points are available from the National Hurricane Center (NHC) at the GIS Data and Products page (http://www.nhc.noaa.gov/gis/), and it should be understood that these are considered preliminary.
Figure 2. Loop of SPoRT 2 km blended (MODIS, NESDIS and REMSS) SST product from Oct 27 0600Z through Oct 29 1800Z. Hurricane Sandy tracks, made available from the NHC GIS and products database are overlain in 6-hourly increments. You may need to click the image twice to get to the looping page.
Figure 3. SST Temperatures
Notice that the storm tracked through a region with SSTs generally above 25C (refer to figure 3 for the sea surface temperature legend for these images), until after it crossed the Gulf Stream heading NW, sometime between 1200Z and 1800Z on the 29th. However, the warmest water in association with the Gulf Stream was aligned to the west of the storm during most of its track. At night, when horizontal temperature gradients were probably larger along/near the Gulf Stream, bands of convection appear to have been favored on the southwestern/western portion of the storm, as captured in these VIIRS Day-night-band (DNB) images below. Of course, other dynamical factors (e.g. low-level streamline convergence, wind shear) also likely played a role in determining the locations of deep convection. As early as the morning of Oct 27th, forecast discussions from the NHC began to note that the strongest and broadest area of hurricane-force winds were located in the storm’s west to southwest flank, in difference to most tropical cyclones in the Northern Hemisphere, where the strongest winds are generally located in the NE or SE quadrants.
Figure 4. VIIRS 0.73 km Day-night-band RGB imagery valid 27 Oct 0642Z, overlain with NHC preliminary track for Hurricane Sandy.
Figure 5. VIIRS 0.73 km Day-night-band RGB imagery valid 28 Oct 0625Z, overlain with NHC preliminary track for Hurricane Sandy.
Figure 6. VIIRS 0.73 km Day-night-band RGB imagery valid 29 Oct 0606Z, overlain with NHC preliminary track for Hurricane Sandy.
Notice that the brightest white clouds and adjacent areas of greater cloud texture (contrasting shadows and light) in these images are indicative of areas of deep convection, which lay mostly to the west/southwest of the center of Hurricane Sandy during its track. To better collocate areas of deep convection with the SSTs, I applied transparency to the VIIRS DNB in the next series of images and conbined the DNB imagery with the SPoRT blended SSTs. It can be seen that development for deep convection favored the warm waters of the Gulf Stream, as might be expected. Perhaps this led to the unusually large storm size and concentration of strongest and broadest hurricane force winds within the SW quadrant of the storm.
Figure 7. VIIRS 0.73 km Day-night-band RGB imagery valid 27 Oct 0642Z (partially transparent), with SPoRT SST blended product and NHC preliminary track for Hurricane Sandy.
Figure 8. VIIRS 0.73 km Day-night-band RGB imagery valid 28 Oct 0625Z (partially transparent), with SPoRT SST blended product and NHC preliminary track for Hurricane Sandy.
Figure 9. VIIRS 0.73 km Day-night-band RGB imagery valid 29 Oct 0606Z (partially transparent), with SPoRT SST blended product and NHC preliminary track for Hurricane Sandy.
Finally, a loop of the best available VIIRS DNB imagery during the track of Hurricane Sandy through the region can be seen below. The last couple of images are after the former hurricane had moved ashore. The last two images in the loop are valid at 0550Z and 0728Z on Oct 30th.
Figure 10. Loop of best available VIIRS 0.73 km DNB RGB images during the track of Hurricane Sandy. The last two images are valid after the storm had come ashore.
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