Bore feature in SAR winds over Lake Michigan

June 6th, 2022 |
RCM2 Wind Speeds, 1152 UTC on 6 June 2022 (Click to enlarge)

Color-enhanced wind speeds observed from Synthetic Aperture Radar (SAR) data on the second RADARSAT Constellation Mission satellite (RCM-2), shown above in AWIPS (Click here for a similar image online at this website) show parallel lines of enhanced wind speeds, a wind structure suggestive of a bore (click here for many previous blog posts on this phenomena), over southern Lake Michigan. Peak wind values (in yellow over the water) are near 14 m/s, with minima in between the lines showing winds around 5-6 m/s. (Note that SAR wind information over land is invalid). When this kind of event happens under mostly clear skies, parallel lines of clouds (that are perpendicular to the observed wind) develop. In this case, widespread clouds prevented satellite detection of cloud bands. The toggles below show Visible (Band 2, 0.64 µm) and Infrared (Band 13, 10.3 µm) at the time of the SAR observations.

GOES-16 Band 2 visible (0.64 µm) and RCM Winds, 1152 UTC on 6 June 2022 (Click to enlarge)
GOES-16 Band 13 infrared (10.3 µm) and RCM Winds, 1152 UTC on 6 June 2022 (Click to enlarge)

Modest convection (cloud tops are only around -48oC) over central Lake Michigan likely generated the bore. For a bore to propagate, a strong inversion is required. Soundings at Green Bay WI and Gaylord MI likely are unrepresentative of the environment over southern Lake Michigan. The sounding at White Lake Michigan — near Detroit — (from this website) does show a surface inversion, as does the sounding at Davenport IA. The cool late-Spring waters of Lake Michigan will serve to anchor a similar low-level inversion over the Lake; bore features travel along those inversions.

Tropical Invest 90L in the Gulf of Mexico

May 22nd, 2022 |

GOES-16 “Red” Visible (0.64 µm) and “Clean” Infrared Window (10.35 µm) images [click to play animated GIF | MP4]

GOES-16 (GOES-East) “Red” Visible (0.64 µm) and “Clean” Infrared Window (10.35 µm) images (above) showed that a decaying Mesoscale Convective System (MCS) produced a low-level Mesoscale Convective Vortex (MCV) over the Gulf of Mexico on 22 May 2022. The coldest MCS overshooting tops exhibited  infrared brightness temperature of -77C around 1401 UTC. GOES-16 Visible (ABI spectral Band 2) Derived Motion Winds tracked MCV cloud motions with velocities as high as 38 knots. As the MCV approached the Gulf Coast, its vorticity to helped to initiate the development of new convection just to the north.

GOES-16 Visible images from the CIMSS Tropical Cyclones site (below) include contours of deep-layer wind shear at 20 UTC — and showed that Invest 90L was moving northward in an environment characterized by low values of shear.

GOES-16 “Red” Visible (0.64 µm) images, with contours of deep-layer wind shear at 20 UTC [click to enlarge]

SAR data over Hawai’i

May 5th, 2022 |
Sentinel-1 SAR data around 0430 UTC overlain on top of GOES-17 ABI Shortwave IR (3.9 µm) at 0430 UTC on 5 May 2022 (Click to enlarge)

This NOAA/OSPO website shows regions where SAR data are available each day. SAR data can also be imported into AWIPS, as shown in the animation above, which animation has the SAR data overlain on top of GOES-17 Band 7 (Shortwave IR, 3.9 µm) data. Note that SAR winds are not valid over the land — the stronger returns over the islands are instead telling you something about the surface. (Compare this image to a Landsat image — there’s a good correlation!)

A zoomed-in version of the imagery over the ?Alenuih?h? Channel between the Big Island of Hawai’i and Maui is shown below as a toggle between the 3.9 µm and the winds. The significant funneling between the two islands is readily apparent, with winds increasing from about 15 knots northeast of the Big Island to closer to 25 knots within the channel.

GOES-17 Band 7 shortwave infrared (3.9 µm) imagery with SAR winds overlain, 0430/0431 UTC on 5 May 2022 (click to enlarge)

A zoom-in over Maui and Molokai, below, details winds around those islands as well, with strong winds between Molokai and Lanai, and an apparent col to the lee of Maui.

GOES-17 Band 7 shortwave infrared (3.9 µm) imagery with SAR winds overlain, 0430/0431 UTC on 5 May 2022 (click to enlarge)

Farther north, over the open Pacific to the north of the Hawai’ian Islands, SAR data shows enhancements in wind underneath structures that are apparent in the Band 7 imagery!

GOES-17 Band 7 shortwave infrared (3.9 µm) imagery with SAR winds overlain, 0430/0432 UTC on 5 May 2022 (click to enlarge)

Tropical Cyclone Malakas in the western Pacific

April 8th, 2022 |
Himawari-8 Band 3 (Visible 0.64 µm) and Band 8 (infrared 6.24 µm) from 0630 to 0700 UTC on 8 April 2022 (Click to enlarge)

The tropical disturbance (formerly 95W) in the western Pacific south of Guam (discussed here) has strengthened and become the second western Pacific named storm of the year: Malakas. The storm is about halfway between the islands of Guam and New Guinea. The side-by-side imagery above, showing Himawari Band 3 and Band 8 imagery (courtesy JMA), shows deep convection near the center of the storm that was at fairly low latitudes: around 6o N at 0600 UTC on 8 April, the times of the imagery above. In addition, the storm is far from dry air. A 24-hour animation of the Band 3 (0.64 µm)/Band 13 (10.41 µm) sandwich product on 7 April 2022 below, taken from this site (see this blog post), shows the rotation of the system and the abundance of convection at the center.

HImawari-8 Sandwich Product, 0000-2350 UTC on 7 April 2022 (Click to enlarge)

The forecast at 1200 UTC on 8 April from the Joint Typhoon Warning Center take this strengthening storm northwest, between Guam and Yap.

Imagery from the SSEC/CIMSS Tropical Weather website, below, shows the storm in a region of low shear. An excellent ASCAT overpass at 1126 UTC on 8 April 2022 showed a closed-off center.

Malakas imagery from the SSEC/CIMSS Tropical Website, data valid between 1126 UTC (ASCAT) and 1500 UTC (Wind shear analysis) (Click to enlarge)