No…just a weak cyclonic vortex off the Atlantic coast of Florida that just happens to look like a tropical cyclone with an eye! GOES-12 visible imagery (above; Java animation) shows the cloud swirl as it developed what appeared to be an “eye” on 20 April 2007. While this vortex was responsible for some weak banded offshore rain features (radar reflectivity image), the GOES-12 10.7 µm IR brightness temperatures were still very warm (around 0º C), indicating a lack of deep convection. The vortex existed in a high-shear environment — around 90 knots on the CIMSS wind shear product (below) — which was not favorable for tropical cyclone development. In addition, the MODIS sea surface temperatures in that region were still below the 80º F (26.7º C) threshold generally considered necessary for tropical cyclone genesis, and GOES sounder total precipitable water values were only in the 20-30 mm (0.79-1.18 inch) range.

The history of this particular swirl is rather interesting. A Weather Channel Blog posting discussed a possible Mesoscale Convective Vortex (MCV) origin; if we follow satellite imagery back in time for a day or two, the development of this feature appears to have been tied to a fairly large mid/upper tropospheric cyclone that was just south of the Great Lakes on 18 April (QuickTime animations: GOES water vapor | GOES IR). A potential vorticity (PV) anomaly associated with the cyclone shows up as a local maximum of GOES Sounder total column ozone (light green to red enhancement on this QuickTime animation); a GFS model cross section through the region of the swirl at 18 UTC on 20 April (below) suggests that a PV “tail” lagging behind the main PV anomaly farther offshore may have played a role in helping to spin up the swirl.

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What would eventually become the largest wildfire in Georgia history (the 472,000 acre Sweat Farm Road / Big Turnaround fire) began to burn in southeastern Georgia (in central Ware county, just south of Waycross, station identifier KAYS) during the afternoon hours on 16 April 2007. Much of that region had been experiencing moderate drought conditions, and high winds that day (gusting to 38 mph at Waycross) helped the fire to grow quickly, forcing some local residents to evacuate their homes. AWIPS images of the MODIS and GOES shortwave IR (3.7/3.9 µm) and IR window (10.7/11.0 µm) channels (above) revealed a significant “hot spot” associated with this fire complex at 03 UTC on 17 April (11 PM on 16 April, local time). Compared to the 4-km resolution GOES image, the 1-km resolution MODIS image offered a more accurate depiction of the shape of the active fire (reported to be 1 mile in width, and 12 miles in length), and also showed another smaller fire that was burning to the east of KAYS at that time. Note that portions of the larger fire were hot enough to saturate the shortwave IR detectors on both MODIS and GOES, yielding black pixels (“NO DATA” pixels) on the AWIPS imagery. McIDAS imagery of the fire hot spots depicted maximum brightness temperatures of 329.0 K (132.5 F) on GOES-12, 330.0 K (134.3 F) on MODIS channels 20/22, and 354.9 K (179.15 F) on MODIS channel 23. In addition, the fire was even hot enough to exhibit “warm pixels” on the IR window channel images (42º C on MODIS, 15º C on GOES). The automated CIMSS Wildfire ABBA product indicated saturated fire pixels over that area as early as 20:15 UTC on 16 April (4:15 PM local time).

It was not possible to locate the hottest fire pixel within the cluster of black “NO DATA” pixels on the AWIPS MODIS Band 20 (3.7 µm) IR images; however, one could use the MODIS Band 7 (2.1 µm) image (below) to pinpoint where the hottest portion of the fire was at that particular time (denoted by the small cluster of “bright” pixels in the upper right panel, near the center of Ware county in Georgia). Although the Band 7 imagery is primarily used for snow/ice detection, this near-IR channel (available during daytime only) will exhibit a signal where the hottest pixels are located — this is due to the fact that higher temperatures shift the peak of the Planck function to shorter wavelengths.

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GOES-12 visible and 3.9 µm shortwave IR imagery (above; Java animation) showed a thick smoke plume drifting southeastward during the day on 17 April; the smoke reduced surface visibilities (as low as 1/2 mile at Jacksonville, Florida) and slowed traffic on area roadways. On McIDAS, the saturated fire pixels “wrapped around” and were displayed as very cold pixels (white enhancement) on the 3.9 µm IR imagery. The land surface beneath the thick smoke plume exhibited a slightly cooler 3.9 µm brightness temperature (lighter gray enhancement), due to a reduction in solar radiation arriving at the surface.MODIS true color imagery (below) indicated that the smoke from this fire had drifted as far as the northern Bahama Islands.

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A record-setting Nor’easter storm system intensified over the eastern and northeastern US on 15 April / 16 April 2007 — this storm produced several tornadoes (including a fatal EF3 tornado near Mulberry, South Carolina), winds of 70-80 mph with a gust to 156 mph (Mount Washington, New Hampshire), waves to 33 feet (Buoy 44025), snowfall up to 23 inches (Locke, New York), 9.30 inches of rainfall (Riverdale, New Jersey), and widespread coastal flooding. QuickTime animations of GOES IR, water vapor, and visible channel imagery from AWIPS reveal the unusually large size of the cloud and water vapor fields associated with this powerful Nor’easter.

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The GOES sounder-derived total column ozone product (above) depicted very high ozone values (400-450 Dobson units, red enhancement) along the western periphery of the storm. A southwest-to-northeast cross section through the storm using GFS model fields (below) show that the dynamic tropopause — assumed to be the 1.5 Potential Vorticity Units (PVU) surface — extended below the 600 hPa pressure level in both the high ozone feature (across northwestern Virginia) and also the core of the 500 hPa low (near Long Island, New York).

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The MODIS Aerosol Optical Depth (AOD) product from the IDEA site (above) showed elevated AOD values over the western Gulf of Mexico on 13 April 2007. This AOD signal (note the hazy appearance on MODIS true color imagery) was due to smoke from agricultural fires that had been burning the previous day in the Yucatan region of Mexico and also in Guatemala. The CIMSS GOES-12 Wildfire ABBA product (below) indicated an increasing number of fire pixels in that area on 12 April; the NOAA Hazard Mapping System (HMS) daily composite from that day also exhibited a significant number of fire pixels in that region (with a large smoke pall drifting over the Gulf of Mexico). A second area of elevated MODIS AOD values was observed over the Gulf of California (MODIS true color image) — this particular AOD signal was due to airborne dust that was lofted into the lower troposphere by strong winds (gusting as high as 86 mph in southern California) associated with a large storm system that was intensifying across the southern Rockies and southern Plains. A QuickTime animation of GOES-12 visible channel images indicated that the dust in the Gulf of California was being transported southward, while the smoke in the Gulf of Mexico was being transported northward.

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