Himawari-9 Clean Window infrared (10.4 µm, Band 13) imagery (every 30 minutes) in late August and early September 2023, above, show the initially looping and later linear path of Typhoon Saola from its development east of the Philippines to its landfall in southern China. Saola was very strong just east of the Philippines before weakening on 27-28 August, then strengthening again as the storm slipped between the Philippines and Taiwan. The temporary weakening is apparent in the SATCON wind plot shown below (taken from the SSEC/CIMSS tropical website).

The animation of Total Precipitable Water from the MIMIC site, below, suggests a reason for the weakening on 27/28 August: dry air was entrained into the storm on 27/28 August. The relatively dry airstream is highlighted in this toggle from 0000 UTC 28 August 2023.

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Deep-layer shear estimates (also from the SSEC/CIMSS Tropical Weather website), below, show Saola developing and traversing a region with relatively low shear values. Increased shear does not appear to have been a big factor in the weakening on 27/28 August 2023.

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5-minute GOES-16 (GOES-East) “Red” Visible (0.64 µm) + Fire Power derived product (a component of the GOES Fire Detection and Characterization Algorithm FDCA), Shortwave Infrared (3.9 µm), “Clean” Infrared Window (10.3 µm) and Fire Temperature RGB images (above) showed signatures of the Game Preserve Fire in northern Walker County, Texas late in the day on 01 September 2023. The wildfire forced evacuations for northwestern portions of Huntsville — and smoke from the fire briefly reduced the surface visibility to 1/2 mile at Huntsville Municipal Airport.

The fire continued to burn after sunset (below), actually intensifying a bit as it advanced westward to within 1/4 mile of Interstate 45 North (causing I-45 N to be temporarily closed to traffic in both directions).

The peak values of GOES-16 Fire Power (1859.75 MW) and 3.9 µm infrared brightness temperature (126.97ºC) occurred at 0101 UTC on 02 September or 8:01 PM local time on 01 September (below). The fire was hot enough that surface 10.3 µm infrared brightness temperatures exceeded 35ºC.

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Overlapping 1-minute Mesoscale Domain Sectors provided 30-second GOES-16 (GOES-East) “Red” Visible (0.64 µm) and “Clean” Infrared Window (10.3 µm) images (with/without an overlay of GLM Flash Extent Density) (above) — which included 15-minute plots of METAR surface reports and hourly plots of Fixed Buoy reports as Category 3 Hurricane Idalia made landfall along the Big Bend coat of Florida at 1145 UTC on 30 August 2023. The hurricane produced winds to 85 mph and rainfall amounts as high as 9.31 inches.

Note that the peak wind gust at the Keaton Beach buoy (KTNF1, located along the coast near the center of the GOES-16 images) was 72 knots at 1100 UTC — then the wind speed dropped to 0 knots (calm) at 1200 UTC as the eye of Idalia moved over that buoy location upon making landfall (below). The raw surface report data indicated that the continuous wind speed was 37.1 m/s (65 knots) at 1120 UTC.

An image (source) of RCM-1 Synthetic Aperture Radar (SAR) winds at 1140 UTC (just prior to the time of landfall) is shown below.

Idalia briefly reached Category 4 intensity, from 0900 UTC until shortly before landfall — 30-second GOES-16 Infrared images (below) showed Idalia during its transition to a Category 4 Hurricane until making landfall.

Several hours prior to landfall, a toggle between VIIRS Day/Night Band (0.7 µm) and Infrared Window (11.45 µm) images from NOAA-20 (mislabeled as NPP) valid at 0715 UTC (above) and Suomi-NPP valid at 0805 UTC (below) showed higher spatial resolution views of Category 3 Idalia. The eye of Idalia passed close to Buoy 42036, where there was a wind gust of 72 knots at 0640 UTC — and the prolonged period of strong winds associated with Idalia caused a notable decrease in water temperature on 30 August (due to the upwelling of cooler sub-surface water).

A larger-scale view of the NOAA-20 VIIRS Day/Night Band image is highlighted in this blog post.

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As noted in this blog post, Radar Constellation Mission (RCM1) Synthetic Aperture Radar (SAR) wind estimates were available over Idalia just before landfall on 30 August 2023, as shown above. RCM1 sampled the hurricane 12 hours before landfall, as well, (All SAR overpasses for Idalia are available online here) Peak winds are just under 60 m/s, and the eye is just offshore. Compare this to the image from 12 hours earlier, below, which image has a maximum wind speed around 55 m/s. The area of strong winds has expanded (green/yellow in the enhancement) between the earlier overpass (below) and the later overpass (above)

How do the SAR winds compare with ABI infrared imagery of the storm? That is shown in the sliders below. AT 2351 UTC on 29 August 2023, the eye of the storm is nearly beneath the warm region in the ABI where an eye might be inferred to be forming (the 29 August/2100 UTC discussion from NHC noted that an eye was forming in satellite imagery).

Just before the 1145 UTC landfall on 30 August, at 1140 UTC, below, SAR winds show the eye just offshore, but the eye in satellite imagery is inland. Why the difference between the SAR/ABI comparison above and below?

At 0000 UTC on 30 August (i.e., just before the earlier SAR overpass shown above), wind shear values over the storm were diagnosed as low as shown below. In contrast, by 1200 UTC on 30 August, just after landfall, at bottom, shear values were considerably larger, and would be displacing the top of the storm to the northeast.

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