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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NOAA-20 overflew Hurricanes Franklin and Idalia shortly after 0700 UTC on 30 August 2023. Ample lunar illumination (the Full Moon occurs on 30 August) meant the Day Night Band yielded very sharp imagery, as shown above. This data was downloaded at the CIMSS Direct Broadcast antenna and processed with CSPP software, yielding the georeferenced image above (more imagery from this overpass is available here; ATMS imagery from the pass is here; both image repositories will be purged in a week). Idalia made landfall along the central Florida coast at about 1145 UTC, four+ hours after the imagery above was captured. Franklin is a larger storm with a much larger eye compared to Idalia.

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A toggle between NOAA-20 (mislabeled as NPP) VIIRS Day/Night Band (0.7 µm) and Infrared Window (11.45 µm) images valid at 0735 UTC on 29 August 2023 (above) showed Tropical Storm Idalia about 1.5 hours before it reached Category 1 hurricane intensity at 0900 UTC. A large convective burst was evident just northeast of the storm center.

Overlapping 1-minute Mesoscale Domain Sectors provided 30-second GOES-16 “Clean” Infrared Window (10.3 µm) images (with/without an overlay of GLM Flash Extent Density) and “Red” Visible (0.64 µm) images during the 10-hour period from 1000-2000 UTC (below). Cloud-top infrared brightness temperatures were as cold as -90C (yellow pixels embedded within darker purple areas) — and occasional bursts of lightning activity were seen.

Odalia had been moving northward across warm Sea Suface Temperatures, and intensified to a hurricane as it traversed a ribbon of high Ocean Heat Content. According to deep-layer wind shear analyses from the CIMSS Tropical Cyclones site (below), Odalia was also moving through an environment of low shear (another factor favorable for intensification).

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A toggle between NOAA-20 (mislabeled as NPP) VIIRS Day/Night Band (0.7 µm) and Infrared Window (11.45 µm) images valid at 0612 UTC on 28 August 2023 (above) showed Hurricane Franklin a few hours before it reached Category 3 intensity.

Franklin rapidly intensified to Category 4 intensity as of 1200 UTC — animations of GOES-16 (GOES-East) “Red” Visible (0.64 µm) images, with/without an overlay of GLM Flash Extent Density (above) and “Clean” Infrared Window (10.3 µm) images (below) showed the hurricane as it moved away from Buoy 41047 during the 1201-1701 UTC period. Abundant lightning activity was seen within the eyewall region — and mesovortices were evident within the eye.

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