Tropical Storm Gordon

September 3rd, 2018 |

NOAA-20 Day/Night Band (0.7 µm) and Infrared Window (11.45 µm) images [click to enlarge]

NOAA-20 VIIRS Day/Night Band (0.7 µm) and Infrared Window (11.45 µm) images at 0636 UTC [click to enlarge]

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

Suomi NPP VIIRS Day/Night Band (0.7 µm) and Infrared Window (11.45 µm) images at 0726 UTC [click to enlarge]

Potential Tropical Cyclone 7 was located between the Bahamas and Florida during the pre-sunrise hours on 03 September 2018. Toggles between VIIRS Day/Night Band (0.7 µm) and Infrared Window (11.45 µm) images from NOAA-20 at 0636 UTC and Suomi NPP at 0726 UTC are shown above (courtesy of William Straka, CIMSS).

The storm became better organized and increased in intensity, and was named Tropical Storm Gordon at 1205 UTC. Animations of GOES-16 (GOES-East) “Red” Visible (0.64 µm) and “Clean” Infrared Window (10.3 µm) (below) showed Gordon as it moved across far southern Florida (where heavy rain and flash flooding occurred) and into the Gulf of Mexico during the daytime hours.

GOES-16

GOES-16 “Red” Visible (0.64 µm) images [click to play MP4 animation]

GOES-16

GOES-16 “Clean” Infrared Window (10.3 µm) images [click to play MP4 animation]

===== 04 September Update =====

GOES-16

GOES-16 “Red” Visible (0.64 µm) images [click to play MP4 animation]

1-minute Mesoscale Domain Sector GOES-16 “Red” Visible (0.64 µm) images (above) and “Clean” Infrared Window (10.3 µm) images (below) showed a series of widespread deep convective bursts within the northeast quadrant of the storm as it moved northeastward toward the Gulf Coast.

GOES-16

GOES-16 “Clean” Infrared Window (10.3 µm) images [click to play MP4 animation]

The GOES-16 Rainfall Rate/QPE product (below) indicated rainfall rates of 2-3 inches per hour were possible from this convection, peaking in the 3-4 inch per hour range just after 1300 UTC. However, Infrared cloud-top brightness temperatures warmed dramatically as the convection moved onshore after about 22 UTC — and the Rain Rate product responded accordingly, with a significant decrease in hourly intensity.

GOES-16 Rain Rate product [click to play MP4 animation]

GOES-16 Rain Rate product [click to play MP4 animation]

Metop-A ASCAT surface scatterometer winds of 39 knots were sampled just northeast of the storm center at 1616  UTC (below).

GOES-16 Rain Rate product with Metop ASCAT winds [click to enlarge]

GOES-16 Rain Rate product with Metop-A ASCAT winds [click to enlarge]

Snow cover in the Brooks Range and North Slope of Alaska

September 2nd, 2018 |

Suomi NPP VIIRS Infrared Window (11.45 µm) images on 01 and 02 September [click to enlarge]

Suomi NPP VIIRS Infrared Window (11.45 µm) images on 01 and 02 September [click to enlarge]

A low moved eastward across the Beaufort Sea on 01 September 2018, bringing a cold front southward across the North Slope and Brooks Range in far northern Alaska (surface analyses). A sequence of Suomi NPP VIIRS Infrared Window (11.45 µm) images (above) showed the clearing of high/cold clouds in the wake of the frontal passage.

The upslope flow of cold air helped to generate accumulating snowfall across that region — prompting a Winter Storm Warning to be issued for the eastern Brooks Range, where 4-8 inches was expected at higher elevations — and some of the resulting snow cover was seen on a Suomi NPP VIIRS Day/Night Band (0.7 µm) image at 1415 UTC or 6:15 am local time on 02 September (below). A comparison with the corresponding VIIRS Infrared Window (11.45 µm) image and Topography is also shown. The darker shades of brown on the topography image correspond to elevations of 6000-8000 feet in the Brooks Range.

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

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

Later in the day on 02 September, additional clearing of patchy low clouds revealed more of the snow cover, as seen in a toggle between VIIRS Visible (0.64 µm), Shortwave Infrared (3.74 µm) and Topography images (below). Supercooled water cloud droplets are efficient reflectors of incoming solar radiation, making patches of low cloud appear darker shades of gray on the Shortwave Infrared image (helping to identify low clouds over snow cover).

Suomi NPP VIIRS Visible (0.64 µm), Shortwave Infrared (3.74 µm) and Topography images [click to enlarge]

Suomi NPP VIIRS Visible (0.64 µm), Shortwave Infrared (3.74 µm) and Topography images [click to enlarge]

At 2124 UTC (or 1:24 pm local time), a 30-meter resolution Landsat-8 False Color Red-Green-Blue (RGB) image viewed using RealEarth (below) provided a more detailed view of a portion of the snow cover. Snow and ice appear as shades of cyan in this type of RGB image — which is created by combining Landsat bands 6 (1.61 µm), 5 (0.865 µm), and 4 (0.655 µm) as Red, Green, and Blue — and numerous small ice floes can also be seen off the coast.

Landsat-8 False Color RGB image [click to enlarge]

Landsat-8 False Color RGB image [click to enlarge]

On a side note, farther to the west an interesting pattern of contrails was seen in VIIRS Visible and Infrared Window images at 2046 UTC (below). On the Visible image, note that the darker contrail shadows cast onto the surface are displaced about 15 miles to the north (due to the low sun angle); the contrail features exhibited Infrared brightness temperatures of -10 to -15ºC. These contrail patterns were generated by military aircraft performing training exercises: similar features have been noted over California and North Dakota.

Suomi NPP VIIRS Visible (0.64 µm) and Infrared Window (11.45 µm) images [click to enlarge]

Suomi NPP VIIRS Visible (0.64 µm) and Infrared Window (11.45 µm) images [click to enlarge]

A curved portion of one of these contrails was seen on web camera images looking south from Atqasuk (below).

 

Upper-tropospheric gravity waves in the wake of a decaying MCS

September 1st, 2018 |

GOES-16 Upper-level Water Vapor (6.2 µm) images [click to play MP4 animation]

GOES-16 Upper-level Water Vapor (6.2 µm) images [click to play MP4 animation]

A series of large Mesoscale Convective Systems (MCS) developed across Nebraska and Iowa during the nighttime hours before sunrise on 01 September 2018, which produced large hail and damaging winds (SPC storm reports). Storm-scale anticyclonic outflow aloft around the periphery of the decaying convection acted as a short-term barrier to the upstream southwesterly winds within the middle/upper troposphere, creating quasi-stationary gravity waves along their rear (westward) edges which persisted for several hours. These waves were most evident over eastern Nebraska and northeastern Kansas on GOES-16 Upper-level Water Vapor (6.2 µm) images (above).

6.2 µm Water Vapor images with plots of GOES-16 Derived Motion Winds (below) intermittently showed these high-altitude anticyclonic winds along the western edges of decaying convection — for example, at 0842 UTC, 0922 UTC, 0957 UTC, 1127 UTC, 1212 UTC and 1312 UTC.

GOES-16 Upper-level Water Vapor (6.2 µm) images, with plots of Derived Motion Winds [click to play MP4 animation]

GOES-16 Upper-level Water Vapor (6.2 µm) images, with plots of Derived Motion Winds [click to play MP4 animation]

The quasi-stationary waves appeared to coincide with a few pilot reports of high-altitude turbulence: Clear Air Turbulence (CAT) was mentioned over northeastern Kansas at 37,000 feet and 39,000 feet, and “mountain wave action” was reported over southeastern Nebraska at 43,000 feet.

Pilot reports of turbulence [click to play animation]

Pilot reports of turbulence [click to play animation]

Higher resolution views of the convection were provided by VIIRS Day/Night Band (0.7 µm) and Infrared Window (11.45 µm) images from Suomi NPP at 0755 UTC and NOAA-20 at 0845 UTC (below). With ample illumination from the Moon (in the Waning Gibbous phase, at 67% of Full), the “visible image at night” capability of the Day/Night Band was well-demonstrated. The coldest cloud-top infrared brightness temperature associated with the MCS in western Iowa was -84ºC — and the effect of a similar “blocking wave” along the western/northwestern edge of that storm could be seen, which was effectively eroding the approaching high-altitude anvil cloud material from the Nebraska MCS. Note that the 0845 UTC NOAA-20 VIIRS images are incorrectly labeled as Suomi NPP.

Suomi NPP VIIRS Day/Night Band (0.7 µm) and Infrared Window (11.45 µm) images, with plots of SPC storm reports [click to enlarge]

Suomi NPP VIIRS Day/Night Band (0.7 µm) and Infrared Window (11.45 µm) images, with plots of SPC storm reports [click to enlarge]

NOAA-20 VIIRS Day/Night Band (0.7 µm) and Infrared Window (11.45 µm) images [click to enlarge]

NOAA-20 VIIRS Day/Night Band (0.7 µm) and Infrared Window (11.45 µm) images [click to enlarge]

Super Typhoon Jebi

August 31st, 2018 |

Himawari-8

Himawari-8 “Clean” Infrared Window (10.4 µm) images [click to play MP4 animation]

West Pacific Typhoon Jebi underwent a period of very rapid intensification on 30 August 2018 (ADT | SATCON), reaching Category 5 Super Typhoon intensity. Himawari-8 rapid-scan (2.5 minute interval) “Clean” Infrared Window (10.4 µm) images (above) showed that Jebi began to exhibit an annular appearance with a nearly symmetric eyewall as it moved through the Northern Mariana Islands (north of Guam). The eye passed just south of the uninhabited volcanic island of Pagan around 16 UTC on 30 August.

Himawari-8 “Red” Visible images (below) revealed mesovortices within the eye of Jebi.

Himawari-8

Himawari-8 “Red” Visible (0.64 µm) images [click to play MP4 animation]

Toggles between VIIRS Day/Night Band (0.7 µm) and Infrared Window (11.45 µm) images from NOAA-20 and Suomi NPP (below) showed more detailed views of (1) the well defined eye, (2) surface mesovortices within the eye, and (3) storm-top gravity waves that were propagating away from the eyewall region. With the Moon in the Waning Gibbous phase (at 77% of Full), ample illumination was available to provide detailed “visible images at night” using the VIIRS DNB.

NOAA-20 Day/Night Band (0.7 µm) and infrared Window (11.45 µm) images at 1602 UTC [click to enlarge]

NOAA-20 VIIRS Day/Night Band (0.7 µm) and infrared Window (11.45 µm) images at 1602 UTC [click to enlarge]

Suomi NPP VIIRS Day/Night Band (0.7 µm) and infrared Window (11.45 µm) images at 1652 UTC [click to enlarge]

Suomi NPP VIIRS Day/Night Band (0.7 µm) and infrared Window (11.45 µm) images at 1652 UTC [click to enlarge]

Convective Rain Rate and Surface Rain Rate products derived from GCOM-W1 AMSR2 data (below) showed the heavy rainfall occurring within the eyewall region and a primary feeder band to the west. VIIRS and AMSR2 images courtesy of William Straka, CIMSS.

GCOM-W2 AMSR2 Convective Rain Rate and Surface Rain Rate products [click to enlarge]

GCOM-W2 AMSR2 Convective Rain Rate and Surface Rain Rate products [click to enlarge]

As Jebi tracked west-northwestward across the West Pacific, products from the CIMSS Tropical Cyclones site showed that it had been moving over waters having high values of Sea Surface Temperature and Ocean Heat Content (below).

Track of Jebi, with Sea Surface Temperature and Ocean Heat Content [click to enlarge]

Track of Jebi, with Sea Surface Temperature and Ocean Heat Content [click to enlarge]

A 48-hour animation of the MIMIC-TC product (below) showed the evolution of the Jebi from 29-31 August. The storm was completing an eyewall replacement cycle near the end of the animation, with the eye becoming distinctly larger.

MIMIC-TC product, 29-31 August

In a comparison of DMSP-16 SSMIS Microwave (85 GHz) and Himawari-8 Infrared Window (10.4 µm) images at 1900 UTC (below), the Microwave data helped to better visualize the structure of the large eyewall in addition to a long, narrow feeder band wrapping inward toward the eye.

DMSP-16 SSMIS Microwave (85 GHz) and Himawari-8 Infrared Window (10.4 µm) images [click to enlarge]

DMSP-16 SSMIS Microwave (85 GHz) and Himawari-8 Infrared Window (10.4 µm) images [click to enlarge]