Gatlinburg, Tennessee wildfire

November 29th, 2016

GOES-13 Shortwave Infrared (3.9 µm) images, with METAR surface reports [click to play animation]

GOES-13 Shortwave Infrared (3.9 µm) images, with METAR surface reports [click to play animation]

Wildfires had been burning in the Great Smoky Mountains for a few weeks (see previous blog posts) as extreme to exceptional drought persisted over the region. However, on 28 November 2016 weather conditions became conducive to extreme fire behavior — and this allowed the Chimney Tops 2 Fire south of Gatlinburg, Tennessee to race rapidly northward (fire perimeter map), driven by strong southerly winds gusting to at least 30-40 knots (as were recorded in Knoxville KTYS, located about 25 miles northwest of Gatlinburg). Widespread evacuations were necessary, and at least 13 fatalities were reported.  4-km resolution GOES-13 Shortwave Infrared (3.9 µm) images (above) showed the development of a fire “hot spot” (the cluster of pixels at the center of the images exhibiting a black to yellow color enhancement) during the day, before clouds moved overhead to mask the fire hot spot signature. The warmest infrared brightness temperature seen during this time period was 326.8 K (brighter yellow pixels) on the 1700 UTC image.

Even though cloud cover was increasing, a detailed view of the fire hot spot was provided by an AWIPS II image of 375-meter resolution Suomi NPP VIIRS Shortwave Infrared (3.74 µm) data at 1815 UTC on 28 November (below). An AWIPS I version of this image is available here. Due to the cloudiness, no discernible hot spot appeared on the lower-resolution 1815 UTC GOES-13 Shortwave Infrared image.

Suomi NPP VIIRS Shortwave Infrared (3.74 µm) image [click to enlarge]

Suomi NPP VIIRS Shortwave Infrared (3.74 µm) image [click to enlarge]

Props to NWS meteorologist Carl Jones for spotting this somewhat unexpected result: the glow of the fire was evident on the following nighttime Suomi NPP VIIRS Day/Night Band (0.7 µm) image, even though there was a thick layer of clouds over the fire itself:


An AWIPS II image comparison of VIIRS Infrared Window (11.45 µm), Shortwave Infrared (3.74 µm) and Day/Night Band (0.7 µm) data at 0816 UTC on 29 November is shown below. Cloud-top Infrared Window brightness temperatures were in the -40 to -55º C range over the fire region (such air temperatures were foundd within the 9.5-10.5 km altitude range on the Nashville sounding when the cloud band was over central Tennessee at 00 UTC). While no fire hot spot signature was evident on the Shortwave Infrared image (due to masking by the clouds), the very distinct bright glow of the fire (which appeared rather large in size, due to scattering of light by the water and ice particles present in the various cloud layers) was seen on the Day/Night Band image. AWIPS I versions of these images are available here.

Suomi NPP VIIRS Infrared Window (11.45 µm), Shortwave Infrared (3.74 µm) and Day/Night Band (0.7 µm) images [click to enlarge]

Suomi NPP VIIRS Infrared Window (11.45 µm), Shortwave Infrared (3.74 µm) and Day/Night Band (0.7 µm) images [click to enlarge]

Additional information is available on the Wildfire Today site (post 1 | post 2 | post 3 | post 4 | post 5).

Hurricane Otto

November 22nd, 2016

GOES-13 Infrared Window (10.7 um) images [click to enlarge]

GOES-13 Infrared Window (10.7 um) images [click to enlarge]

As a follow-up to the previous Otto blog post, GOES-13 Infrared Window (10.7 um) images (above) showed Otto around the time that it became the latest hurricane on record to form in the Caribbean Sea on 22 November 2016 (NHC advisory).

A comparison of GOES-13 Visible (0.63 um) and Infrared Window (10.7 um) images (below) revealed multiple convective bursts during the day, some of which exhibited IR brightness temperatures of -80º C and colder (violet enhancement). Because of Otto’s central dense overcast, no eye was apparent in the GOES-13 imagery; even on a DMSP-16 SSMIS Microwave (85 GHz) image at 2049 UTC the eyewall was not fully closed.

GOES-13 0.63 um Visible (top) and 10.7 um Infrared Window (bottom) images [click to animate]

GOES-13 0.63 um Visible (top) and 10.7 um Infrared Window (bottom) images [click to animate]

===== 24 November Update =====

GOES-13 Infrared Window (10.7 µm) images, with hourly surface reports [click to play MP4 animation]

GOES-13 Infrared Window (10.7 µm) images, with hourly surface reports [click to play MP4 animation]

As Otto slowly approached the coast of southern Nicaragua on 24 November, it rapidly intensified (SATCON plot) to a Category 2 hurricane. GOES-13 Infrared Window (10.7 µm) images (above; also available as a 36 Mbyte animated GIF) and Visible (0.63 µm) images (below; also available as a 18 Mbyte animated GIF) showed the development of an eye just offshore, which rapidly filled as the storm moved inland after 17 UTC on 24 November and began to interact with the terrain. After crossing Nicaragua and Costa Rica, an eye was once again discernible around 02 UTC on 15 November (as Otto emerged over the Pacific Ocean).

 

GOES-13 Visible (0.63 µm) images, with hourly surface reports [click to play MP4 animation]

GOES-13 Visible (0.63 µm) images, with hourly surface reports [click to play MP4 animation]

Before the formation of an eye, a Suomi NPP VIIRS Infrared Window (11.45 µm) image at 0639 UTC (below; courtesy of William Straka, SSEC) showed the presence of cloud-top gravity waves propagating westward along the Nicaragua/Costa Rica border; these waves were likely a response to deep convective bursts offshore near the center of Otto.

Suomi NPP VIIRS Infrared Window (11.45 µm) image [click to enlarge]

Suomi NPP VIIRS Infrared Window (11.45 µm) image [click to enlarge]

A comparison of DMSP-17 SSMIS Microwave (85 GHz) and GOES-13 Infrared Window (10.7 µm) images around 1115 UTC on 24 November (below) revealed a much larger (albeit not completely closed) eye signature using the microwave data.

DMSP-17 SSMIS Microwave (85 GHz) and GOES-13 Infrared Window (10.7 µm) images around 1145 UTC [click to enlarge]

DMSP-17 SSMIS Microwave (85 GHz) and GOES-13 Infrared Window (10.7 µm) images around 1145 UTC [click to enlarge]

Otto became the southernmost landfalling hurricane on record for Central America. It was also the strongest hurricane on record for so late in the season within the Atlantic basin.

DMSP-18 SSMIS Microwave (85 GHz) image [click to enlarge]

DMSP-18 SSMIS Microwave (85 GHz) image [click to enlarge]

A DMSP-18 SSMIS Microwave (85 GHz) image at 0043 UTC on 25 November (above) showed that the eye of Otto was still well-defined as it began to move into northern Costa Rica (making this the first hurricane or tropical storm on record for that country). The eye structure could be tracked on MIMIC-TC imagery (below) as it moved inland from the Atlantic Ocean, across far southern Nicaragua and far northern Costa Rica, and eventually emerged over the Pacific Ocean after about 03 UTC on 25 November.

Morphed MIMIC-TC imagery, 24-25 November [click to enlarge]

Morphed MIMIC-TC imagery, 24-25 November [click to enlarge]

===== 26 November Update =====

Suomi NPP VIIRS Infrared Window (11.45 µm) and Day/Night Band (0.7 µm) images [click to enlarge]

Suomi NPP VIIRS Infrared Window (11.45 µm) and Day/Night Band (0.7 µm) images [click to enlarge]

As Tropical Storm Otto was weakening during its west-southwestward motion over Pacific Ocean waters with low Ocean Heat Content, nighttime images of Suomi NPP VIIRS Infrared Window (11.45 µm) and Day/Night Band (0.7 µm) data at 0744 UTC on 26 November (above; courtesy of William Straka, SSEC) displayed shorter-wavelength cloud-top gravity waves on the Infrared image and longer-wavelength mesospheric airglow waves (reference) on the Day/Night Band image (all of which were propagating west-southwestward away from the deep convective cluster near the center of Otto). Bright lightning streaks were also seen on the Day/Night Band image.

More facts on the historic aspects of Otto are available from The Weather Channel and Weather Underground; see the National Hurricane Center and the CIMSS Tropical Cyclones websites for the latest information on this storm.

Gravity waves (and a land breeze boundary) in the Gulf of Mexico

November 22nd, 2016

GOES-13 Visible (0.63 µm) images, with hourly surface/buoy/ship reports [click to play animation]

GOES-13 Visible (0.63 µm) images, with hourly surface/buoy/ship reports [click to play animation]

GOES-13 Visible (0.63 µm) images (above) revealed a series of gravity waves propagating southeastward across the Gulf of Mexico on 22 November 2016. These waves appeared to be moving through or along the tops of the marine boundary layer stratocumulus cloud field; since the hourly winds from surface/buoy/ship reports were  generally from the southeast/east/northeast, these gravity waves were not likely surface-based.

Also of note was an apparent land breeze boundary that moved west-northwestward away from the Yucatan Peninsula of Mexico during the day.

Suomi NPP VIIRS Visible (0.64 µm) image, with NUCAPS sounding locations and surface analysis [click to enlarge]

Suomi NPP VIIRS Visible (0.64 µm) image, with NUCAPS sounding locations and surface analysis [click to enlarge]

Gravity waves like those observed here are usually ducted within a strong air temperature inversion — so Suomi NPP NUCAPS (NOAA-Unique CrIS/ATMS Processing System) soundings around 1828 UTC (above) were examined for evidence of such an inversion. Training material for NUCAPS Soundings in AWIPS is available here.

One of the NUCAPS vertical profiles of temperature and moisture is shown below, for a point over the southern Gulf of Mexico (designated by the cyan rectangle, approximately 50 miles northwest of the coast of the Yucatan Peninsula) — several of the waves had passed through this location prior to the image time. A well-defined temperature inversion did indeed exist aloft, within the 1-2 km layer above the surface (and just above the top of the moist marine boundary layer, where the stratocumulus cloud field existed). It therefore appears likely that this series of southeastward-moving gravity waves was mildly perturbing the tops of the stratocumulus clouds.

NUCAPS sounding profile for a point over the Gulf of Mexico, north of the Yucatan Peninsula [click to enlarge]

NUCAPS sounding profile for a point over the Gulf of Mexico, north of the Yucatan Peninsula [click to enlarge]

Since there were no nearby surface frontal boundaries or areas of organized deep convection inland over the southern US during the preceding 24 hours, it is unclear as to what may have been the catalyst for these gravity waves.

Late-season Tropical Storm Otto in the southwest Caribbean Sea

November 21st, 2016
ascatwinds_1433utc_21nov2016

Metop-A Scatterometer winds at 1430 UTC and GOES-13 10.7 µm Brightness Temperature (Click to enlarge)

A late-season tropical depression has formed in the southwestern Caribbean Sea. The morning Metop-A pass on 21 November 2016 allowed ASCAT scatterometer winds to be sampled over the system: rain-flagged values near tropical storm force were present as shown above. A similar image (from this site) is available here, and also here (from this site).

GOES-13 Infrared (10.7 µm) Brightness Temperatures (Click to animate)

Infrared (10.7 µm) imagery from GOES-13, above, from 1315 through 1715 UTC on 21 November, shows periodic deep convection over the Depression; the grey regions in the deepest convection over the system correspond to brightness temperatures colder than -75 C. The environment surrounding this system, shown below, is marginally favorable for strengthening; sea-surface temperatures are warm, although the oceanic heat content suggests the warmth does not extend through a deep column of water. Wind shear over the storm is modest (but far stronger north of the storm). (Imagery below is from this site). The system is forecast to become a tropical storm within the next 24 hours.

Sea-surface temperatures, Oceanic Heat Content and Wind Shear (Click to enlarge)

Update: Otto was named a tropical storm at 2100 UTC 21 November; GOES-13 Visible (0.63 µm) Imagery is shown below. Numerous tropical overshooting tops can be seen during the course of the day.

GOES-13 Visible (0.63 µm) Imagery on 21 November 2016 (Click to animate)

MIMIC Total Precipitable Water fields, below, show that Otto emerged from a region of persistent deep moisture over the southwestern Caribbean Sea that has been contracting as the storm formed. This region of moisture was focused along the intersection of a stalled and decaying Atlantic frontal zone and the Pacific monsoon trough (hourly animation).

MIMIC Total Precipitable Water fields at 2100 UTC on 17,18,19,20 and 21 November (Click to enlarge)

DMSP-16 Microwave (85 GHz) imagery, below, showed evidence of a closed eye associated with Otto at 2132 UTC.

DMSP-16 SSMIS Microwave (85 GHz) image [click to enlarge]

DMSP-16 SSMIS Microwave (85 GHz) image [click to enlarge]