Super Typhoon Atsani reached Category 5 intensity early in the day on 19 August 2015; the storm displayed a nearly annular eyewall signature during much of the day on Himawari-8 infrared (10.4 µm) images (above; click image to play MP4 movie file). A large (64 Mbyte) animated GIF is available here. Evidence of low-altitude mesovortices within the eye can be seen in the 2-km resolution infrared images.

A comparison of DMSP SSMIS microwave (85 GHz) and MSAT-2 infrared (10.8 µm) images around 20 UTC is shown below (courtesy of the CIMSS Tropical Cyclones site).

On the topic of eye mesovortices, a more detailed view of these features could be seen on daylight 0.64 µm visible images (below; click image to play MP4 animation). A large (28 Mbyte) animated GIF is available here.

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An EF-1 Tornado struck Lake Geneva, WI after sunset on 18 August 2015 (SPC Storm Reports; NWS MKX report). GOES-14 was in SRSO-R mode, providing 1-minute imagery over the region; additionally, GOES-13 was in RSO mode, providing imagery about every 7 minutes. Unfortunately, GOES-14 requires two 15-minute breaks in scanning to perform housekeeping (Link); one of those periods is from 0130-0145 UTC, 13 minutes before the tornado touchdown at 0158 UTC. (GOES-R will not require these 15-minute breaks). The animation above pauses during that housekeeping time; it also slows for the ten minutes surrounding 0158 UTC. (Click here for an animation without the White Box signifying Lake Geneva).

The 0158 UTC imagery from GOES-14 (paired with the 0155 UTC imagery from GOES-13 is shown below. An overshooting top that is associated with the tornado is apparent (northeast of Lake Geneva because of the parallax shift). This overshoot is easily traceable in the 1-minute imagery, above, as it moves northeastward towards Lake Michigan. The feature also appears and can be tracked in GOES-13.

Automated detection of Overshooting Tops (and thermal couplets) (from this website) showed a cluster of Overshooting Tops moving over southeast Wisconsin at the time of the tornado. The number of Overshoots detected jumped about an hour before the tornado touchdown.

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Himawari-8 captured the trek of Typhoons Goni (on the left) and Atsani (on the right) as they moved across the central Pacific Ocean on Monday 17 August 2015 (animation also available here as an mp4). Goni has passed through the northern Mariana Islands and is forecast to fluctuate in intensity as it moves towards Asia. Atsani’s predicted path is towards the northwest; it is forecast to intensify to a Category 5 Super Typhoon. Both storms are moving across very warm ocean waters (Goni, Atsani), and deep layer wind shear values are low (below). Sea Surface Ttemperature and Wind Shear products are available from the CIMSS Triopical Cyclones site.

Late in the day on 17 August, a comparison of MTSAT-2 infrared (10.8 µm) and DMSP SSMIS microwave (85 GHz) imagery of Category 3 Typhoon Atsani around 2232 UTC (below) showed a rather ragged-looking eye on the infrared image and evidence of a eyewall replacement cycle (ERC) occurring on the microwave image. The ERC process often indicates that a change in tropical cyclone intensity will soon take place.

What is remarkable in this case of “twin typhoons” in the West Pacific basin is that the MIMIC-TC product indicated that both Atsani and Goni were undergoing ERCs at about the same time (below).

A multi-day YouTube animation of Himawari-8 10.35 µm infrared imagery shows the upscale development of Goni and Atsani in the central Pacific. The loop runs from 13 August through 1200 UTC on 18 August.

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A comparison of 4-km resolution GOES-15 (GOES-West), GOES-14, and GOES-13 (GOES-East) 3.9 µm shortwave infrared images (above; click to play MP4 animation; also available as a 9.4 Mbyte animated GIF) showed the development and evolution of the “hot spot” (dark black to yellow to red color enhancement) associated with a small wildfire that formed near the border of Fergus and Petroleum counties in central Montana during the afternoon hours on 15 August 2015. With GOES-15 Routine Scan mode “SUB-CONUS” sectors, images were available up to 6 times per hour (at :00, :11, :15, :30, :41, and :45); with GOES-13 in Rapid Scan Operations (RSO) mode, images were available up to 8 times per hour (at :00, :07, :15, :25, :30, :37, :45, and :55). The GOES-14 satellite had been placed into Super Rapid Scan Operations for GOES-R (SRSO-R) mode, providing images at 1-minute intervals to emulate what will be available with mesoscale sectors from the ABI instrument on GOES-R.

For the central Montana wildfire, the first unambiguous signature of a darker black wildfire hot spot began to appear on each satellite after about 1945 UTC, with the first color-enhanced pixels (signifying a shortwave IR brightness temperature of 331.9 K) showing up on the 2026 UTC GOES-14 image. The hottest fire pixel  on the GOES-15 images was 336.5 K at 2130 UTC, while the hottest fire pixel on GOES-13 images was 329.8 K at 2125 UTC. From 2120 to 2130 UTC, the hottest GOES-14 fire pixels were 341.2 K (the saturation temperature of the 3.9 µm detectors on that satellite).

With the finer spatial resolution of the shortwave IR detectors on the polar-orbiting MODIS (1-km) and VIIRS (375-meter) instruments, a fire hot spot was first detected on the 1857 UTC VIIRS image (below).

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