SAR data over Hurricane Fiona

September 19th, 2022 |
Sentinel SAR wind speeds over Hurricane Fiona, 2245 UTC on 19 September 2022 (Click to enlarge)

NOAA/NESDIS STAR is producing occasional SAR imagery over Hurricane Fiona (link). NetCDF files can be imported into AWIPS and displayed, as shown above (color-enhanced with Beaufort Scaling), in an image from late on 19 September when Fiona was just north of Hispaniola. The strongest winds were associated with the northern eyewall of the storm, and an asymmetry in the storm is apparent (The NHC discussion from 2100 UTC on 19 September (here), and the discussion at 0300 UTC on 20 September (here) will give more context). The Radial wind analysis at the SAR link (here) shows the strongest winds in the NW and NE quadrants of the storm, with a peak near 100 knots. The toggle below, from late on 19 September, compares GOES-16 ABI Clean window (10.3 µm) imagery and the Sentinel SAR wind estimates (with a different color enhancement). A parallax shift in the GOES-16 imagery means the two eyes do not overlay.

GOES-16 Band 13 infrared (10.3 µm) imagery and Sentinel SAR windspeeds, 2245 UTC on 19 September 2022 (Click to enlarge)

Update on 23 September: RADARSAT-2 overflew Fiona at 2236 UTC on 22 September. The toggle below shows SAR winds estimated at that time, with peak values in the eyewall near 100 knots (for more information on this SAR pass, including a more complete image over the eye, click here). There is a parallax shift in the high clouds of the storm; Fiona at this time was near 30.5oN, 69.3oW, far from the sub-satellite point at 0oN, 75.2oW: the parallax shift for the high clouds will be away from the sub-satellite point. The time difference in the observations — 5 minutes — should not cause a big shift for a storm moving at 17 knots (i.e., 20 mph) to the north-northeast.

RADARSAT-2 SAR observations over Fiona, 2236 UTC on 22 September 2022 along with GOES-16 Clean Window Band 13 (10.3 µm) infrared imagery at 2230 UTC (Click to enlarge)

Parallax shifts in VIIRS views of Fiona

September 19th, 2022 |

VIIRS Day Night Band visible (0.7 µm) imagery from Suomi NPP (0549 UTC) and NOAA-20 (0638 UTC) on 19 September 2022 (Click to enlarge)

Suomi NPP and NOAA-20 both overflew Hurricane Fiona (NPP flew overhead to the east, NOAA-20 flew overhead to the west) in the early morning of 19 September 2022, as shown above in imagery created at AOML (The Atlantic Oceanagraphic and Meteorological Laboratory) and displayed at the Direct Broadcast site there. The images appear to show an eastward motion of the eye — but GOES-16 animations, below, show a persistent west-northwest motion (landfall occurred in the Dominican Republic around 0730 UTC).

GOES-16 Band 13 Infrared Imagery (10.3 µm), 0301 – 0946 UTC on 19 September 2022 (Click to enlarge)

The apparent eastward motion of the eye also shows up in the infrared imagey, which rules out artifacts related to shadowing.

VIIRS M15 (10.8 µm) infrared imagery from Suomi-NPP (0549 UTC) and NOAA-20 (0636 UTC) on 19 September 2022 (Click to enlarge)
Suomi NPP Day Night Band imagery and GOES-16 Band 13 Infrared imagery, ca. 0556 UTC on 19 September 2022 (Click to enlarge)

This might be an example of a Parallax shift in VIIRS imagery causing a shift in a feature. NOAA-20’s nadir was over Jamaica, considerably to the east of the Mona Passage where Fiona’s eye was developing. A parallax error may be responsible, because satellite navigation will place the tall clouds farther from the sub-satellite point than observed.

The full-resolution Day Night band imagery from Suomi NPP, and from NOAA-20 (both available from the CIMSS ftp site here and here) show strong convection starting ca. 0530 UTC and continuing through ~0630 UTC near the eye.