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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Tropical Storm Idalia has formed in the northwestern Caribbean Sea, in between Cuba and Mexico. The True-Color mp4 animation above, taken from CSPP Geosphere site (direct link to the animation), shows active convection over the Caribbean that is coalescing around the low-level circulation center (located near 20^oN, 85.5^oW at 2100 UTC on 27 August)

A still image from 2236 UTC on 27 August, below, shows GOES-16 Band 13 “Clean Window” infrared (10.3 µm) imagery overlain on top of the derived SSTs from 2200 UTC. Very warm water — upper 80s to low 90s degrees Fahrenheit — is diagnosed along Idalia’s forecast path in the eastern Gulf of Mexico. Band 13 Brightness Temperatures are very cold: near -80^oC.

Microwave imagery from the CIMSS Tropical Website, below, show that Idalia in the afternoon of 27 August 2023 was not a poorly-organized lopsided storm. Much of the deepest convection was south of the center (as might also be inferred from the asymmetric distribution of cold cloud tops around the center in the infrared imagery above).

The toggle below shows the forecast path of Idalia into the northwestern Gulf of Mexico along with plots of Oceanic Heat Content — a measure of how deep the warm waters are — and atmospheric shear. Idalia is forecast to traverse very warm waters as shown in the SST plot above. The narrow Loop Current in the Gulf of Mexico is where the warm surface waters are least likely to be cooled by storm-induced mixing. In addition, the shear fields show Idalia moving into a less favorable shear environment. Strengthening is expected.

Note that Idalia’s position allows imagery from the CIMSS Direct Broadcast site to show information, for example channel 18 (183 GHz from NOAA-21), or VIIRS True Color from Suomi NPP (an image that includes both Idalia and Hurricane Franklin over the Atlantic Ocean). Direct Broadcast imagery for Idalia is also available from AOML.

Interests along the northeastern Gulf Coast and in the southeastern United States should pay close attention to Idalia’s path. Refer to the National Hurricane Center for the latest information on Idalia.

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