SAR data collection over Cyclone Freddy in the Indian Ocean has led to a remarkable collection of imagery. To date, more than twenty eye overpasses have occurred from RADARSAT-2 (3 overpasses), Sentinel 1A (1 overpass) and the three satellites of the RADARSAT Constellation Mission (17(!) overpasses). The animation above shows images tracking the system as it moves across the Indian Ocean towards a projected landfall in Madagascar. Eye-centered imagery, below, shows the organization and strengthening of the system.

Because 5 satellites are involved, occasionally imagery that is very close in time is acquired. For example, RCM-3 and RADARSAT-2 both sampled the between 2236 and 2240 UTC on 11 February 2023; RCM-1 and RADARSAT-2 both sampled the eye near 0000 UTC on 16 February (Freddy was near its peak intensity at that time, as noted in this blog post); RCM-1 and Sentinel-1A both sampled the eye near 0020 UTC on 17 February 2023. Three toggles showing these comparisons are below. Note that winds at the edge of a scan are likely weaker than they actually are.

SAR Winds and analyses for Cyclone are Freddy are also available here. For more information on Freddy, refer to the JTWC webpages, or the RSMC in La Reunion (map of all RSMCs is here), or the SSEC/CIMSS Tropical Weather Website.

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GOES-18 (GOES-West) Air Mass RGB images during the 15-19 February 2023 period (above) displayed the migration of a Kona Low from north of the main Hawaiian Island chain on 15 February toward Johnston Island on 19 February. The MIMIC Total Precipitable Water product (below) showed that the circulation of this Kona Low helped to draw a broad plume of moisture northwestward from the ITCZ  and across Hawai’i — providing the fuel for a prolonged period of heavy rainfall.   

Plots of rawinsonde data from Hilo (below) revealed the deep tropical moisture that was present over the eastern portion of the Big Island from 18-19 February.

GOES-18 “Clean” Infrared Window (10.3 µm) images (above) provided a closer look at the Big Island, where the heaviest rainfall occurred across the Kau, Puna and South Hilo districts (NWS Honolulu PNS). On 18 February, Hilo experienced 2 consecutive hours with rainfall in excess of 3 inches (below).

Hilo, Hawai'i, with over 3" rain in consecutive hours. The 2-hour total of 6.16" has a recurrence interval of > 50 years. Looking at the hourly records (since 1962), only one other instance of consecutive hours each having 3"+ rain (Nov 2, 2000). pic.twitter.com/41fnxiUojA

— Brian Brettschneider (@Climatologist49) February 18, 2023

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True Color RGB mages — created using Geo2Grid — from GOES-18 (GOES-West), GOES-17 and GOES-16 (GOES-East) (above) displayed the hazy signature of blowing dust associated with a Tehuano wind event, which was spreading south-southwestward from the Gulf of Tehuantepec across the Pacific Ocean on 18 February 2023. A narrow rope cloud marked the edges of this outflow.

GOES-16 “Red” Visible (0.64 µm) images (above) include plots of surface/ship/buoy reports and the 18 UTC surface analysis — a region with the risk of Gale Force winds was outlined in the Gulf of Tehuantepec.

In a closer view of regional topography (below), the narrow Chivela Pass could be seen north-northeast of Ixtepec (station identifier MMIT), through which the northerly flow of cold air is accelerated.

A sequence of ASCAT wind barbs (source) from Metop-B and Metop-C (below) helped to highlight the pulse of gap winds as they emerged from the Isthmus of Tehuantepec and spread south-southwestward across the Gulf of Tehuantepec.

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Sentinel-1A SAR data just before sunrise captured a very narrow region of enhanced winds just south of the Rio Grande delta on 18 February 2023, as shown above in a toggle with the 1226 UTC GOES-16 Band 13 Clean Window infrared (10.3 µm) imagery. There appears to be no obvious relationship between the wind structures and the brightness temperatures at this time. However, an animation of the infrared imagery for the 3 hours before sunset, below, shows a similar north-south linear feature, in about the same place as the SAR winds, between 1000 and 1100 UTC. (Here’s a toggle of the 1224 UTC Sentinel winds and the 1036 UTC Band 13 imagery).

The 1200 UTC surface analysis (click here) from the 18th shows the Texas Gulf Coast near a ridge axis with easterly winds indicated. However, the Sentinel-1A wind analysis, shown below (from this website; direct link to image), shows convergence into the line of stronger winds. The normalized radar cross-section (NRCS) image (here, or here at the NOAA/STAR website), from that same website, shows evidence of small-scale gravity waves on the western edge of the wind maxima. Those fields are visible in the AWIPS imagery as well.

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