The animation below, showing GOES-16 Clean Window infrared imagery (Band 13, 10.3 µm; processed using geo2grid, v1.1), tracks the named storm Don, first named as Subtropical Storm Don at 0900 UTC on 14 July, reclassified as Tropical Depression Don at 1500 UTC on the 17th, and upgraded to a Tropical Storm at 0300 UTC on the 18th, and to a hurricane at 2100 UTC on the 22nd. The animation shows the storm periodically affected by shear (when the low-level circulation is separated from the deep convection), especially on the 14th of July.

A closer view using 10-minute GOES-16 Visible and Infrared images on 22 July (above) showed Tropical Storm Don developing a distinct eye, before being upgraded to a Hurricane at 2100 UTC. The coldest cloud-top infrared brightness temperatures were around -60ºC (darker shades of red).

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On 24 July, Long-lived Don, devoid of convection, was deemed extra-tropical. This occurred while Don was moving north of the domains shown above. The last tropical advisory was issued at 1500 UTC.

For more information on Don, refer to the National Hurricane Center’s website. Don presents no current threat to land.

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GOES-18 (GOES-West) Day Land Cloud Fire RGB, Shortwave Infrared (3.9 µm), “Clean” Infrared Window (10.3 µm) and Visible images with an overlay of the Fire Power derived product — Fire Power is a component of the GOES Fire Detection and Characterization Algorithm FDCA — (above) showed thermal signatures associated with a wildfire that produced a pair of pyrocumulonimbus (pyroCb) clouds in Canada’s Northwest Territories late in the day on 21 July 2023.

At 2300 UTC, the 3.9 µm infrared brightness temperature reached 90.85C, with a Fire Power value of 3623 MW (below). Located at a latitude of 67.35N, this wildfire was only about 40 miles south of the Arctic coast.

The 2 pyroCb clouds began to form at 2340 UTC and 0010 UTC — when pyrocumulus jumps were evident in the RGB and Visible images. Cloud-top 10.3 µm infrared brightness temperatures eventually were as cold as -54.7C.

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Sentinel-1A overflew Hawai’i and Maui near sunrise on 20 July 2023, measuring the surface winds surrounding those islands. The mp4 animation above (click here for an animated gif) shows GOES-18 visible imagery (Band 2, 0.64 µm) from 1601 to 1801 UTC. The animation includes toggles at 1616 UTC when Sentinel 1A data resulted in wind measurements. (Sentinel-1A winds are available at this website — note that this is a new url!; this website shows global views of Normalized Radar Cross Section (NRCS) data.) The strong winds in the channel can be inferred by the swift motion of the clouds there compared to elsewhere during the animation. Note also how the high terrain of Hawai’i and Maui are effectively blocking the low-level flow around those islands.

The 1616 UTC imagery are shown side by side below (the visible image grey scale upper bound is reduced in the image from the default 130 to 25). The strong winds through the Alenuihaha channel (20-30 knots, and closer to 35 knots just south of Maui) are apparent, and many wind gradients in the SAR data are associated with GOES-18 visible imagery features.

SAR Satellites operate on a 12-day repeat cycle. Sentinel-1A will take observations in this same region 12 days after 20 July, i.e., on 1 August.

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GOES-18 Night Microphysics imagery from 19 July 2023, above, shows a disorganized Tropical Storm Calvin moving south of Hawai’i before sunrise on 19 July. The low-level swirl of the system is apparent to the south of the Big Island; convection associated with the system develops during the animation over Hawai’i, and high clouds with the system are present to the east of Hawai’i. Convection produced heavy rains that closed some roads. The CPHC discussion on the storm at 1500 UTC (link) noted the separation between the surface and mid- and upper-level features. Visible imagery, below, a bit later than the animation above, shows the obvious low-level swirl (still associated with occasional isolated convection), but by 2100 UTC, the system was declared post-tropical.

By 0800 UTC on 20 July 2023, the system had weakened to an open-wave as shown in the Advanced Scatterometer (ASCAT) image shown below from Metop-C. Winds of 30-35 knots are still indicated, but no westerly winds Equatorward of the strong easterly winds are present.

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Calvin brought extraordinary moisture to the Hawai’ian islands. The 1200 UTC sounding at Hilo, below, (also available here) showed Total Precipitable Water exceeding 2.5″! That value, if verified, means this is one of the top 5 wettest soundings at that location according to the SPC Sounding Climatology site. MIMIC Total Precipitable Water values, shown at bottom in the animation from 0000 UTC 19 July to 0000 UTC 20 July, show the moisture associated with the storm.

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The identification of the low-level circulation at night in this case was not difficult, perhaps because high clouds were not present over the low-level circulation. The toggle below shows Night Microphysics and the Day Night Band visible image (the New Moon occurred on 17 July, so very little lunar illumination was present). The low-level swirl is apparent in both images.

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