Sentinel-1A overflew the Samoan Islands on 4 September — as it does every 12 days — and the Normalized Radar Cross Section data (as at this website) was used to create wind data at very high spatial resolution. Sentinel-1A derived wind data can also be viewed at this NOAA/STAR website that has links to both NRCS data and wind speeds. The wind data shown in the animation above was plotted in AWIPS to facilitate comparison to infrared imagery. Sometimes, there are obvious relationships between the SAR wind features and ABI imagery. In the case shown above, that’s a challenge. The ABI data does show high clouds sinking south towards Samoa and low-level cloud streets moving west-northwest. Peak winds near 30 knots are north of Upolu and east of Savai’i. There is an ABI feature associated with that wind, but it would be difficult to relate reliably all similar ABI features to wind maxima. It is far more challenging to relate the smaller wind maxima that suggest a relationship with cloud streets/showers to ABI structures. It is possible to estimate the wind direction however given the presence of wind shadows downwind of the islands, especially Tutuila.

The Slider below that compares the SAR Wind speeds shows the difficulty in relating the SAR winds to Band 13 imagery.

View only this post Read Less

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.

---

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.

View only this post Read Less

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.

View only this post Read Less

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.

View only this post Read Less